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1. Fill in the blanks: 1. According to the procedure for obtaining measurement results, measurement is divided into direct measurement and indirect measurement. 2. According to whether the instrument is in contact with the measured object, measurement is divided into contact measurement and non-contact measurement. 3. Whether it is a simple instrument or a complex instrument, its components can be regarded as consisting of three links: sensor, transducer, and display according to function. They are connected by signal lines or signal pipelines. 4. In the International System of Units, the unit of temperature is Kelvin. 5. The symbol of thermodynamic temperature is T, and its unit name is Kelvin. 6. The symbol of the thermodynamic temperature unit is K, and its definition is 1/273.16 of the thermodynamic temperature of the triple point of water. 7. The symbol of Celsius temperature is t, its unit name is Celsius, and the unit symbol is ℃. 8. The relationship between thermodynamic temperature and Celsius temperature is t=T-273.16. 9. The liquid-in-glass thermometer consists of a temperature sensing bag filled with working liquid, a capillary tube, and a scale scale. 10. Liquid-in-glass thermometers can be divided into rod thermometers, internal standard thermometers, and external standard thermometers according to their structures. 11. Liquid-in-glass thermometers can be divided into industrial, laboratory, and standard mercury thermometers according to their uses. 12. Industrial liquid-in-glass thermometers are generally made of internal scale type, while laboratory liquid-in-glass thermometers are generally rod-type. 13. A thermocouple is composed of two conductors of different properties welded or twisted. 14. If the temperatures at both ends of the thermocouple are different, thermoelectric potential will be generated in the thermocouple circuit. 15. The end of the thermocouple welded is called the hot end, and the end connected to the wire is called the cold end. 16. Commonly used temperature measurement thermocouples in thermal power plants include K type, J type and S type. 17. Thermal resistance thermometer measures temperature based on the characteristic that the resistance value of conductors and semiconductors changes with temperature. 18. Industrial thermal resistance consists of five parts: temperature sensing element, insulating tube, inner lead, protective sleeve, and junction box. 19. Thermal resistors have a wide temperature measurement range and high accuracy. Platinum thermal resistors are often used as standard thermometers in the range of -200 to +500°C. 20. There are two types of secondary meters that are often used with thermocouples to measure temperature: millivolt meters and electronic potentiometers. 21. Electronic automatic balancing bridge is used as a secondary meter and is often used in conjunction with thermal resistors to measure temperature. 22. The compensation wire has the same thermoelectric characteristics as the thermocouple in the range of 0 to 100. 23. There are three types of thermal resistors commonly used in industry: platinum resistance, copper resistance, and nickel resistance. 24. Copper thermal resistors are generally only used for humidity measurement in moisture-free and non-corrosive media below 150°C. 25. In the International System of Units, the unit of pressure is Newton/meter 2, also called Pascal, and its symbol is Pa. Its definition is the pressure generated by a force of 1 Newton acting uniformly vertically on an area of 1 meter 2. 26. 1 Pascal is equal to 1.01971×10-5 Kgf/cm2 27. 1 Pascal is equal to 0.987×10-5 physical atmospheric pressure 28. 1 Pascal is equal to 1.01971×10-4 meters of water column 29. 1 kg/cm2 pressure is equal to 10 meters of water column. 30. The accuracy level of the pressure gauge is expressed by the reference error. 31. For pressure gauges with one-way scales, the allowable error is calculated as a percentage of the upper limit of measurement. 32. For a pressure gauge with a two-way scale, the allowable error is calculated as a percentage of the sum of the upper and lower measurement limits. 33. For pressure gauges without zero scale, the allowable error is calculated as the percentage of the difference between the upper and lower measurement limits. 34. When choosing to use a pressure gauge, in order to make the pressure gauge work safely and reliably, the range of the pressure gauge should be selected to be 1/3 higher than the measured pressure value. 35. When installing a pressure gauge, the selection of sampling points should be representative, and the measuring point should not be selected in a place with eddy currents. 36. Generally, the distance between the sampling point and the installation point of the pressure gauge should not exceed 50 meters. 37. The tapping displacement of the pressure gauge is the movement of the pointer position caused by tapping the case at the same point. 38. There are three accuracy levels of industrial pressure gauges: 1.0, 1.5, and 2.5. 39. There are three accuracy levels of standard pressure gauges: 0.25, 0.4, and 0.6. 40. When the medium measured by the pressure gauge is corrosive, an isolation tank containing neutral medium must be installed in front of the pressure gauge. 41. When the medium measured by the pressure gauge has high temperature, in order to prevent the high-temperature medium from directly entering the pressure gauge when installing the pressure gauge, a condensation pipe must be installed in front of the pressure gauge. 42. If the connection part of the liquid column pressure gauge sampling tube is not tight, the indication will be too small. 43. The "zero point migration" of the pressure transmitter is to migrate the measured parameter value corresponding to the zero point of the transmitter from zero to a non-zero value. 44. When the pressure gauge is undergoing pressure increase calibration and pressure reduction calibration, after tapping the case at each corresponding calibration point, the difference between the two readings is called the variation of the pressure gauge. 45. Regulations stipulate that the variation of industrial pressure gauges shall not exceed the absolute value of the allowable basic error. 46. When measuring violently fluctuating pressure, a vibration damping device should be installed in front of the pressure gauge. 47. Instantaneous flow rate is the amount of material passing through a certain section of the pipeline per unit time. 48. The cumulative flow rate is the amount of material passing through a certain section of the pipeline within a certain period of time. 49. Standard throttling components include standard orifice plates, standard nozzles, long-diameter nozzles, Venturi tubes, etc. 50. The pressure taking methods of standard orifice plates include corner joint pressure taking and flange pressure taking, etc. 51. The standard nozzle pressure measurement method is only corner pressure measurement. 52. For main steam flow measurement in thermal power plants, nozzles are often used as throttling components. 53. For thermal power plant feed water flow measurement, orifice plates are often used as throttling components. 54. For the measurement of small flow and low Reynolds number fluid flow, rotor flow meters are often used. 55. The zero point of the drum water level of a high-pressure drum boiler is generally set at 50 mm below the geometric center line of the drum. 56. Commonly used interface position measurement methods include static pressure, ultrasonic, nuclear radiation, buoyancy, electrical, weighing, etc. 57. Static pressure devices for measuring liquid level are divided into several types according to their structure: connector, differential pressure type, pressure type, etc. 58. In thermal power plants, the most widely used method for measuring boiler drum water level is the differential pressure water level gauge. 59. The electric contact water level meter consists of two parts: a water level sensor and an electrical display instrument. 60. The sensor of the electric contact water level meter is a connector with several electric contacts. 61. When the pressure in the boiler drum is close to the critical pressure, the electric contact water level meter cannot be used to measure the water level. 62. When the boiler is operating normally, the water level in the drum shown by the water level gauge of the connecting device is lower than the actual water level. 63. Because the electrodes of the electric contact water level meter are installed on the measuring tube at a certain distance, the output signal is stepped. 64. In thermal power plants, the level of pulverized coal is mostly measured using heavy-duty level meters, ultrasonic level annunciators, piezoelectric level meters, etc. 65. The oxygen content in the boiler flue gas reflects the size of the excess air coefficient a. Therefore, by measuring the oxygen content of the flue gas, the combustion conditions in the boiler can be known. 66. In thermal power plants, the magnetic oxygen meter and the oxidation oxygen meter are mainly used to measure the oxygen content in the boiler flue gas. 67. The oxygen concentration difference potential output by the zirconia oxygen meter is not only related to the oxygen content in the gas on both sides of the zirconia, but also related to the temperature. 68. In thermal power plants, there are three types of measuring meters for turbine speed: mechanical, electrical, and digital. 69. The digital tachometer uses a photoelectric sensor and a magnetoresistive transmitter to convert the rotational speed into a frequency signal. Within a specified standard time, the measuring circuit accumulates the frequency signal, and then displays the rotational speed digitally. 70. The sensor of the electrical tachometer is a tachometer generator. 71. The SS-46 two-way vibration meter is an absolute vibration meter, and its measurement result is the absolute value of the amplitude. 72. Electronic belt scales and track scales are often used to measure the amount of raw coal in thermal power plants. 73. In power plants, differential transformers are often used as sensors for some important position measurements of steam turbines. 74. In hydrogen-cooled generators, the measurement of hydrogen purity is particularly important. At present, the sensors for measuring hydrogen purity mostly use thermal conductivity cells. 2. Judgment 1. √ In terms of graduation value, 1℃ is equal to 1K. 2. The value expressed by ×Celsius temperature unit "Celsius" should be written as "20 degrees Celsius" or "20℃". 3. √The temperature reflects the average kinetic energy of the molecules of the object. 4. √The so-called temperature scale is a numerical representation method of temperature. It uses physical quantities that change with temperature to represent temperature values. 5. √The temperature scale is the scale of temperature. 6. √The Celsius temperature scale is also called the percentage temperature scale. It stipulates that the freezing point of pure water under standard atmospheric pressure is zero degrees and the boiling point is 100 degrees. The two points are divided into 100 equal parts, and each equal part represents one degree Celsius. 7. × The technical index for evaluating the quality of temperature measuring instruments mainly depends on the maximum absolute error of the instrument. 8. √Bimetal thermometers are expansion thermometers. 9. × Moving coil thermometer is a non-contact temperature measuring instrument. 10. × Those who measure humidity below 600℃ are collectively called cryometers, and those who measure temperatures above 600℃ are collectively called pyrometers. 11. × Pressure thermometers are liquid expansion thermometers. 12. √The thermoelectric potential of a thermocouple is a function of the temperature difference between the two ends of the thermocouple and is nonlinear. ； In different temperature ranges, the temperature difference is equal, but the thermoelectric potential is not equal. 13. √ Insert the third and fourth conductors into the thermocouple loop. As long as the temperatures at both ends of the inserted conductor are equal and the inserted conductor is homogeneous, no matter what the temperature distribution of the inserted conductor is, it will not affect the size of the original thermocouple thermoelectric potential. 14. √ The cold end compensator must be matched with the thermocouple. Different types of thermocouples should use different cold junction compensators. 15. √Any two conductor materials can be formulated into thermocouples. 16. √The thermocouple indexing table is made under the condition that the cold end temperature is 0°C. When used, the cold end temperature is required to be 0°C. If the cold end temperature is not 0°C, the cold end temperature must be corrected to 0°C. 17. ×The purity verification of the thermal resistor is the inspection and verification of the material components that constitute the thermal resistor. 18. √The connection between the thermal resistor and the secondary meter generally adopts the three-wire connection method, mainly to reduce the measurement error caused by the change of the line resistance with the ambient temperature. 19. × Moving coil temperature instruments can be divided into millivolt meter type and unbalanced bridge type. The millivolt meter type is used for temperature measurement in conjunction with thermal resistors, and the unbalanced bridge type is used in conjunction with thermocouples. 20. √ When judging the positive or negative of a K-type thermocouple, it can be identified according to its magnetophilicity. If it is not magnetophilic, it is the positive pole, and if it is slightly magnetophilic, it is the negative pole. 21. × Temperature measuring instruments manufactured according to different principles have the same requirements for the resistance value of the thermocouple loop. 22. √ When using a platinum-rhodium-platinum thermocouple to measure temperature, incorrectly using the compensation wire of a nickel-chromium-nickel aluminum thermocouple and connecting the polarity correctly will cause over-compensation and make the indicator meter high. 23. √The external circuit resistance of the thermometer millivolt meter must be specified. 24. Use a three-wire system to connect the thermal resistance element and the meter. The lengths of the three wires must be equal. 25. ×The basic unit of pressure in the International System of Units is MPa. 26. ×A physical atmospheric pressure is an engineering atmospheric pressure. 27. √Atmospheric pressure changes with time and location. 28. √ When using a piston pressure meter, the piston, piston cylinder, load-bearing plate and weight must be used together. 29. × Regulations stipulate that the use of piston pressure gauges requires an ambient temperature of 0°C. 30. × The pressure transmitter installed below the sampling point should use positive migration to correct its zero point. 31. √ When there is a linear error in the spring tube pressure gauge, the movable screw of the tie rod should be adjusted. 32. √ When reading the height of the liquid column of a liquid column pressure gauge, the data is generally read on the scale according to the position of the apex of the meniscus of the liquid column. 33. √ Use transformer oil for low-pressure piston pressure gauges, and castor oil for high-pressure ones. 34. √DBY pressure transmitter realizes zero point migration mainly by installing a migration spring on the lever. 35. √ When checking the sealing of the pressure gauge and transmitter, generally use a piston pressure gauge, pressurize to the highest measurement value, and keep it for 5 minutes. If the measuring element does not leak or expand, it means the sealing is qualified. 36. √When it is necessary to take pressure near the valve, if the pressure taking point is selected in front of the valve, the distance to the valve must be greater than twice the pipe diameter. 37. √ Used as a second-class standard transmission pressure gauge, its accuracy level is ±0.2% 38. √ Double bellows differential pressure gauge is mainly used to measure fluid flow in conjunction with a throttling device. 39. √ To measure pipeline flow, not only must there be qualified throttling components, but also the straight pipe sections before and after it must meet the requirements. 40. √ When using a dynamic pressure measuring tube to measure flow, the flow is actually indirectly measured by measuring the average flow velocity of the fluid. 41. ×When using a throttling device to measure flow, a rectifier must be installed in the pipe in front of the throttling device. 42. √ Glass rotor flowmeter is a non-standardized instrument. It is calibrated with water at normal temperature and pressure during manufacture. If the type, working status and physical parameters of the actual measured medium are different from the factory calibration, it will cause a large measurement error. 43. × In thermal power plants, the flow rate-area method is often used to measure the main steam flow rate. 44. × In thermal power plants, orifice plates are often used to measure air flow. 45. When the boiler is operating normally, the drum water level interface is horizontal and clear. 46. √ When using a weighing position meter, the shape of the container must be certain, and the height of the medium must be proportional to the weight. 47. √ When using a balance container to measure water level, changes in drum pressure cause severe changes in the saturated water and saturated water vapor, which is the main cause of measurement errors. 48. × The more electrodes the electric contact water level meter has, the higher the measurement accuracy and the better the reliability. 49. × Using a zirconia oxygen meter, the oxygen content in a relatively stable gas in a certain space can be measured. 50. × Electronic track scale is a device that can continuously measure the amount of coal transported on the track, and its output signal changes continuously. 51. √The output voltage of the tachogenerator is proportional to the rotation speed of the turbine. 3. Choice 1. The accuracy level of the instrument is represented by which of the following errors: CA, system error ； B. Absolute error ； C. Allowable error 2. The symbol of thermodynamic temperature is B A, K ； B, T ； C, t 3. There is a temperature measuring instrument with an accuracy level of 0.5 and a measuring range of 400 to 600°C. The allowable basic errors of the meter are CA, ±3 B, ±2 C, ±1. 4. A thermometer that is not suitable for measuring fluctuations in room temperature is A. A. Steam pressure thermometer B. Rod thermometer C. Bimetal thermometer 5. At the same temperature, the thermocouple that generates the largest thermoelectric potential is C A. Platinum-rhodium-platinum thermocouple ； B. Nickel-chromium-nickel silicon thermocouple C. Nickel-chromium-copper thermocouple 6. The thermocouple with the highest accuracy is A A. Type S B. Type K C. Type J 7. Which of the following types of thermocouples has the best linear relationship between thermoelectric potential and temperature C A, S type B, R type C, K type 8. The thermocouple whose positive and negative polarity can be judged by magnetophilicity is B A, B type B, J type C, S type 9. Among the following thermocouples, which one is a non-standardized thermocouple B A, nickel chromium-nickel silicon ； B. Nickel chromium-nickel aluminum ； C. Iron-Constantan 10. When using a thermocouple to measure a temperature above 0, if the polarity of the compensation wire connected to the secondary meter is reversed, the indicated value CA will be higher. ； B. Normal ； C. Low 11. The output thermoelectric potential of a nickel-chromium-nickel silicon thermocouple is 33.29 millivolts. It is known that the ambient temperature of its cold end is 20°C. Check the nickel-chromium-nickel silicon thermocouple scale table and find that the corresponding temperature of 33.29 millivolts is 800°C. Then the temperatures of its hot end are B A, 800°C B, 820°C C, and 780°C. 12. When using an iron-constantan thermocouple to measure temperature, the compensation wire of a platinum-rhodium-platinum thermocouple is mistakenly used, which will cause the indicator to be AA and low. ； B. The indication is on the high side ； C. The indication is normal ； 13. Among the following thermal resistors, the non-standardized thermal resistors are A, A, and germanium thermal resistors. ； B. Platinum thermal resistance ； C. Copper thermal resistance ； 14. There are several temperature measuring devices as follows. When measuring the temperature of turbine bearing bush, it is best to use CA, nickel-chromium-nickel silicon thermocouple. ； B. Inflation pressure thermometer ； C. Platinum thermal resistance ； 15. There is a platinum-rhodium-platinum thermocouple. Let E (300,50) be X, E (500,250) be Y, and E (250,0) be Z. Then C A, X = Y = Z ； Ｂ、Ｘ＝Ｙ≠Ｚ ； C、X≠Y≠Z ； 16. In the International System of Units, the units of pressure are A, Pa, B, bar, C, and MPa. 17. There is a pressure gauge with an accuracy of level 1.0 and its range is -0.1~1.6MPa. The allowable error is B A, ±0.016MPa. ； B. ±0.017 MPa ； C, ±0.015 MPa ； 18. The indication value of the liquid column pressure gauge is too small. The reason is that A. A. The pressure guide pipeline is not tightly sealed. ； B. The pressure guide tube is blocked ； C. The air vent end is blocked ； 19. A spring tube pressure gauge has a linear error. AA, adjust the movable screw of the tie rod. ； B. Change the angle between the sector wheel and the tie rod ； C. Replace hairspring ； 20. If a spring tube pressure gauge has a nonlinear error, you should B A. Adjust the movable screw of the tie rod. ； B. Change the angle between the sector wheel and the tie rod ； C, A and B are adjusted simultaneously ； 21. The pointer of the spring tube pressure gauge jumps and rotates. The possible reason is that B A. The elasticity of the spring tube is large. ； B. The connection between the connecting rod and the sector wheel is pressed too tightly. ； C. The scale is not concentric with the axis ； 22. During the process of calibrating a spring tube pressure gauge, it was found that during the rising and falling processes, the same calibration point varied greatly, which could not be eliminated no matter how much adjustment was made. The reason was that A. A. the spring tube was deformed. ； B. The spring tube is not tight ； C. Sector gear wear ； 23. To calibrate an industrial pressure gauge with an accuracy of level 1.5 and a range of 6.0MPa. The accuracy and range of the selected standard pressure gauge are CA, level 0.4, and 16MPa. ； B, level 0.6, 10MPa ； C, 0.25 level, 10MPa ； 24. When the pressure gauge is installed at a higher position above the sampling point, its zero point A A adopts positive correction. ； B. Use negative correction ； C. No correction required ； 25. There is a pressure measuring point. If the maximum pressure being measured is 10MPa, the range of the selected pressure gauge should be AA, 16MPa B, 10MPa C, 25MPa. 26. For a force balance pressure transmitter with a double-lever structure, when a migration spring is used for zero point migration, its output characteristics C A, the slope remains unchanged, and the range changes. ； B. The slope changes, but the measuring range remains unchanged. ； C. The slope and range remain unchanged. ； 27. If the transmission mechanism of the spring tube pressure gauge is not clean, its B A and zero points will be higher. ； B. Large variation ； C. Range decrease ； 28. The indication of the Hall pressure transmitter is too small in the full range. The reason is that B A. The Hall element is stuck. ； B. Hall film deteriorates ； C. No control current input ； 29. When calibrating the diaphragm differential pressure gauge, A, A, and U-shaped tubes should be used ； B. Piston pressure gauge ； C. Single tube pressure gauge ； 30. When the pulsating pressure is measured, the range of the selected pressure gauge should be C A, 1.5 times B, 1 times C, and 2 times the measured value. 31. The standardized throttling device is A A. Venturi tube. ； B. Eccentric orifice plate ； C. Wing-shaped dynamic pressure tube ； 32. It is best to use CA and Roots flowmeter to measure the flow rate of the boiler air pipe. ； B. Orifice plate ； C. Wing-shaped dynamic pressure tube ； 33. The volume measurement method is used by B A. Turbine flow meter ； B. Roots flow meter ； C. Electromagnetic flowmeter ； 34. What the flow accumulator records is B A. Instantaneous flow ； B. Accumulated flow ； 35. In thermal power plants, AA and target flow meters are commonly used to measure fuel flow. ； B. Standard orifice plate ； C. Rotameter ； 36. During normal operation of the boiler, the ratio of the water level shown by the mica water level gauge on the steam drum to the actual water level in the steam drum is C A. On the higher side ； B. Equal ； C. Low ； 37. When using a differential pressure transmitter with an output signal of 4 to 20 as the drum water level transmitter, when the drum water level is at zero, the transmitter output is B A, 4mA B, 12mA C, 20mA 38. The SS-46 two-way vibration meter has an output when the vibration is large, but there is no output when the vibration is weak. The reason is C A. The pickup coil is open circuit ； B. The pickup coil is short-circuited ； C. There is friction between the vibration pickup coil and the magnetic steel. ； 39. To obtain accurate measurement results, the working temperature of the zirconia oxygen meter must be around B A and 500°C. ； B. Around 850℃ ； C. Around 1200℃ ； 40. At present, the meter with the highest accuracy for measuring turbine speed is D A. Centrifugal mechanical tachometer ； B. Speed measuring generator ； C. Magnetic tachometer ； D. Digital tachometer ； Q&A: 1. What is measurement? Measurement is the process of comparing the measured quantity with the unit standard quantity used through experiments to find its value. 2. What is a measuring instrument? Comparing the measurand with its unit using experimental methods requires certain equipment. It inputs the measurand and outputs the ratio of the measurand to the unit. This equipment is called a measuring instrument. 3. What is the true value of the measurement result? The true value of the measurement result refers to the true size of the measured physical quantity at a certain moment, a certain position or a certain state. Generally, the results measured by standard instruments are regarded as the true value. 4. What is measurement error? measurement error: The difference between the measurement result and the true measurement value is usually called measurement error. Measurement error has size, plus or minus and unit. 5. What is the absolute error of indication value? The algebraic difference between the indicated value of the instrument and the true value being measured is called the absolute error of the indicated value. 6. What is the relative error of indication value? The ratio of the absolute error of the indication to the actual value being measured is called the relative error of the indication. 7. What is the reference error of indication value? The ratio of the absolute error of the indication to the upper limit or range of the instrument is called the reference error of the indication, expressed as a percentage. 8. What is the basic error of the instrument? Under the specified technical conditions, the indication value of the instrument is compared with the indication value of the standard meter. During the process of steady increase and decrease of the measured value, the maximum of the reference errors of the indication values obtained in the full range of the instrument is called the basic error of the instrument. 9. What is systematic error? When the same quantity is measured multiple times under the same conditions, the size and sign of the error remain constant or change according to certain rules. This error is called a systematic error. Generally, the changing patterns and causes can be found out through experiments or analysis, and the measurement results can be corrected after determining the numerical magnitude and direction. 10. What is accidental error? When the same quantity is measured multiple times under the same conditions, the size and sign of the error are irregular and cannot be estimated in advance. This type of error is called accidental error. 11. What is gross error? Errors that significantly distort the measurement results are called gross errors, or gross errors for short. 12. What is the sensitivity of the instrument? Sensitivity is the ability of an instrument to respond to a measured value, usually defined as a change in output caused by a change in input. * L changes to the input * The ratio of X. It is one of the important indicators to measure the quality of the instrument. If the sensitivity of the instrument is high, the number of digits in the indication value can be increased. However, it should be noted that the sensitivity must be compatible with its allowable error. Too many digits cannot improve the measurement accuracy. 13. What is the resolution of an instrument? The resolution of the instrument is also called discrimination, which indicates the ability of the instrument to respond to small changes in the input quantity. Insufficient resolution will cause resolution error, that is, when the measured value changes by a certain value, the indication value remains unchanged. This error is called the insensitive zone or dead zone. 14. What are the thermal measurement parameters of thermal power plants? Generally there are temperature, pressure, flow, material level and composition, as well as rotation speed, mechanical displacement and vibration. 15. What is the significance of measuring temperature in a thermal power plant? In the heat production process of power plants, temperature is an important parameter to ensure safe and economical power generation. If the temperature of the superheated steam is not well controlled, the superheater and water-cooled wall tubes may burst due to overheating. When the steam drum and cylinder are started and stopped, if the temperature is uneven, dangerous stress will occur. If the exhaust gas temperature is higher than the design value, the efficiency of the boiler will be reduced. If the main steam temperature is lower than the design value, the efficiency of the steam turbine will also be reduced. This will cause energy loss, consume more fuel, reduce power generation, and affect economic benefits. Therefore, accurate temperature measurement is very important to ensure the safety of the power plant production process and improve economic efficiency. 16. There are many thermometers used in thermal power plants. Which categories are they classified according to their working principles? (1) Pressure gauge thermometer ； (2) Glass tube liquid thermometer ； (3) Bimetal thermometer ； (4) Resistance thermometer ； (5) Thermocouple thermometer ； (6) Radiation pyrometer. 17. Explain what properties of substances the pressure gauge thermometer measures based on? The temperature measurement substances of pressure gauge thermometer include inert gas, liquid and saturated steam. It uses the properties of constant volume gas, liquid thermal expansion and contraction pressure changes or saturated steam saturation pressure changes to measure temperature. Its basic structure is a closed system composed of a temperature sensing element, a capillary tube, and a deformation element spring tube. 18. Briefly describe the temperature measurement process of a pressure gauge thermometer? When measuring temperature, insert the temperature bulb into the medium to be measured. When the temperature of the medium changes, the temperature-sensing material in the temperature bulb expands or contracts due to the increase or decrease in temperature, causing the pressure to increase or decrease, causing the curvature of the spring tube to change and its free end to shift. The connecting rod and transmission mechanism drive the pointer to rotate, and the temperature value is directly displayed on the dial. 19. What types of pressure gauge thermometers are there? Pressure gauge thermometers are divided into indicating type, recording type, alarm type and regulating type according to their uses. According to different filling materials, they can be divided into gas pressure thermometers, vapor pressure thermometers and liquid pressure thermometers. 20. Briefly explain what are the characteristics of a pressure gauge thermometer? (1) Small vibration impact ； (2) Low accuracy ； (3) The time constant is large. 21. What is the operating principle of a pressure gauge thermometer with electrical contacts? The pressure gauge thermometer with electric contacts not only has an indication part, but also has electric contacts for two-position adjustment or control. The upper and lower limit contacts of the electrical contact device can be adjusted to any given temperature as needed. The upper and lower limit temperatures are indicated by the fixed contacts, and the movable contacts are driven by the pointers. When the temperature of the measured medium exceeds or falls below the temperature set by the upper or lower limit, the moving contact on the thermometer pointer comes into contact with the upper or lower limit contact. At this time, a signal is sent to close or disconnect the control loop, which plays a regulatory role. 22. Briefly describe the working principle of liquid-in-glass thermometer? The liquid-in-glass thermometer measures temperature by utilizing the properties of the temperature-sensing liquid's thermal expansion and contraction that cause the height of the liquid to change. When the temperature-sensing package is subject to changes in the measured medium, the temperature-sensing liquid begins to expand or contract, and the liquid rises or falls along the capillary tube, thereby directly displaying the temperature value on the scale. 23. What are the advantages and disadvantages of liquid-in-glass thermometers? Liquid-in-glass thermometers have the following advantages compared with other temperature measuring instruments:: 1. Simple structure, cheap and easy to manufacture ； 2. Has high accuracy ； 3. Direct reading, easy to use. shortcoming: It is easily damaged and cannot be repaired. Mercury-in-glass thermometers are prone to produce mercury hazards during production and pollute the environment when damaged. 24. What is the temperature measurement principle of bimetal thermometer? Two bimetallic sheets with different linear expansion coefficients are stacked and welded together as a measuring element. When the temperature changes, the bimetallic sheet bends due to the different linear expansion coefficients of the two metals. The temperature is measured using the property that the bending degree is proportional to the temperature. 25. What are the characteristics of bimetal thermometer? The bimetal thermometer has the characteristics of wide temperature measurement range -100-600, high accuracy of 0.5, large scale, long scale lines, easy to use and not easy to be damaged. 26. What is the temperature measurement principle of resistance thermometer? The temperature measurement principle of the thermal resistor is based on the fact that the resistance of the conductor and semiconductor material changes with the change of temperature. The resistance of the thermal resistor is measured using a display instrument to obtain the temperature value corresponding to the resistance value. 27. What are the characteristics of resistance thermometer? 1. It has high accuracy. 2. High sensitivity, strong output signal, easy to measure, display and realize long-distance transmission. 3. The resistance-temperature relationship of metal thermal resistors has good linearity, and has good reproducibility and stability. However, it is large in size and has large thermal inertia, which is not conducive to dynamic temperature measurement and cannot measure point temperature. 28. What is a standardized thermal resistance? Standardized thermal resistance refers to the current * * Thermal resistors produced by Uni-President have specified R0 values and resistance temperature coefficients, and have certain allowable errors. They have uniform resistance-temperature scales and supporting secondary instruments produced by Uni-President. 29. What types of industrial standardized thermal resistors are there? at present * * There are three types of industrially standardized thermal resistors produced in a unified manner: WZB type platinum resistance, WZG type copper thermal resistance, WEN type nickel resistance 30. What is a non-standardized thermal resistance? Non-standardized thermal resistance refers to the current * * There is no unified production of thermal resistors, no unified resistance-temperature scale, and no unified supporting instruments, so they are generally made together with the indicating part to form a thermometer. 31. What types of non-standardized thermal resistors are there? There are thermistors, carbon thermal resistors, indium thermal resistors, and germanium thermal resistors. 32. What parts does an industrial temperature measuring thermal resistor consist of? Industrial temperature measuring thermal resistance generally consists of four parts: temperature sensing element, protective sleeve, connecting wire and junction box. 33. What is an armored thermal resistor? Armored thermal resistors are made by combining metal protective sleeves, insulating materials and resistors. They are also called sleeve thermal resistors. 34. What are the characteristics of armored thermal resistors? Features: 1. Small thermal inertia and rapid response ； 2. It has good mechanical properties and can withstand strong vibration and impact. ； 3. Except for the head of the thermal resistor, other parts can be bent arbitrarily, which is suitable for installation on equipment with complex structures for temperature measurement. ； 4. The resistor body is covered by a metal sleeve and insulating material, which is not susceptible to corrosion by harmful media and has a long service life. 35. What are the common faults that occur when using thermal resistance elements? Common faults of thermal resistors: 1. The thermal resistance wires are short-circuited or grounded. ； 2. The thermal resistance wire is disconnected ； 3. Water accumulation in the protective casing ； 4. The lead wire between the resistor element and the junction box is broken. 36. What are the structural characteristics of the special thermal resistor used to measure the metal temperature of steam turbine bearings? Due to the particularity of the use environment and requirements, its structure is different from that of general thermal resistors. Generally, double wires of enameled copper wire or platinum wire are densely wound on the insulated frame, and the end face should be in close contact with the bearing bush of the bearing to reduce thermal conduction errors. 37. How many calibration methods are there for thermal resistance components? (1) Graduation calibration method: That is, measure the resistance value at different temperature points to see whether its relationship with temperature meets the regulations. (2) Purity verification method: That is, at 0°C and 100°C, measure the resistance values R0 and R100, and find the ratio R100/R0 of R100 and R0 to see if it meets the requirements. 38. Briefly describe the principle of thermocouple temperature measurement? The basic principle of temperature measurement with flat thermocouples is the thermoelectric effect. Connect any two different conductors or semiconductors to form a closed loop. If the temperatures of the two contacts are not equal, a thermoelectromotive force will be generated in the loop and a thermal current will be formed. This is the thermoelectric effect. A thermocouple is made of two different metal materials welded at one end. The welded end is called the measuring end, and the unsoldered end is called the reference end. If the temperature of the reference end is constant, the size and direction of the thermoelectric potential are only related to the characteristics of the two materials and the temperature of the measuring end, and there is a fixed functional relationship between the thermoelectric potential and temperature. Using this relationship, as long as the size of the thermoelectric potential is measured, the purpose of measuring temperature can be achieved. 39. What factors determine the thermoelectric characteristics of a thermocouple? The thermoelectric properties of a thermocouple are determined by the chemical composition and physical properties of the electrode material. The size of the thermoelectric potential is only related to the material of the thermocouple and the temperature at both ends, and has nothing to do with the thickness and length of the thermocouple wire. 40. What conditions must be met for a thermocouple to generate thermoelectric potential? 1. The thermocouple must be composed of two conductor and semiconductor materials with different properties but meeting certain requirements. 2. There must be a temperature difference between the measuring end and the reference end of the thermocouple. 41. What is the content of the homogeneous conductor law of thermocouples? The electric potential of a thermocouple composed of two homogeneous metals has nothing to do with the diameter, length of the hot electrode and the temperature distribution along the length of the original hot electrode. It is only related to the hot electrode material and the temperature at both ends. The thermoelectric potential is the difference between the functions of the temperatures at both ends. If the temperatures at both ends are equal, the thermoelectric potential is zero. If the material is uneven, when the temperature is different everywhere on the hot electrode, additional thermoelectric potential will be generated, causing unpredictable measurement errors. 42. What is the law of the middle conductor of thermocouples? In the thermocouple loop, when the third or fourth conductors are inserted, as long as the temperatures at both ends of the inserted conductor are equal and the inserted conductor is homogeneous, no matter what the temperature distribution of the inserted conductor is, it will not affect the size of the thermoelectric potential of the original thermocouple. 43. What is the content of the intermediate temperature law of thermocouples? The thermoelectric potential of a thermocouple when the junction temperature is t, t0 is equal to the algebraic sum of the corresponding thermoelectric divisions of the thermocouple when the junction temperature is t, tn and tn, t0, that is: EAB(t,t0)= EAB(t,tN)+ EAB(tn,t0) 44. What are the parts of an industrial thermocouple? Thermal electrode, insulating tube, protective sleeve, junction box. 45. What types of thermocouples are there according to their structural forms? 1. Ordinary industrial thermocouple. 2. Armored thermocouple. 3. Multi-point thermocouple. 4. Small inertia thermocouple. 5. Surface thermocouple. 46. What are the main types of common industrial thermocouples? Commonly used common industrial thermocouples currently include: (1) Platinum rhodium 10-platinum thermocouple ； (2) Platinum rhodium 30-platinum rhodium 6 thermocouple ； (3) Nickel chromium-nickel silicon thermocouple ； (4) Iron-Constantan thermocouple ； (5) Copper-Constantan thermocouple ； (6) Nickel-chromium-copper thermocouple ； (7) Nickel-chromium-constantan thermocouple. 47. What is a standardized thermocouple? The so-called standardized thermocouples refer to several thermocouples that are relatively mature in technology, widely used, can be produced in batches, have excellent and stable performance, and have been included in industrial standard documents. These thermocouples have a unified indexing meter, which is very convenient to use, and have matching display instruments. Standardized thermocouples of the same model are interchangeable. 48. What is a non-standardized thermocouple? Non-standardized thermocouples are not mature in technology and are not widely used at present. They are only used in certain special environments, such as high and low temperatures. This kind of thermocouple is inferior to the standardized thermocouple in terms of scope and quantity. At the same time, there is no unified index meter and no matching display instrument. 49. What is a standard thermocouple? The so-called standard thermocouple refers to a thermocouple used as a standard to verify practical thermocouples. The physical and chemical properties are very stable and have certain limit errors. 50. What is an armored thermocouple? Armored thermocouples are solid combinations made of hot electrodes, insulating materials and metal sleeves, also called sleeve thermocouples. 51. What are the characteristics of using thermocouples to measure temperature? (1) High measurement accuracy ； (2) Simple structure ； (3) Fast dynamic response ； (4) Long-distance measurement is possible ； (5) Wide temperature measurement range ； 52. What are the advantages of armored thermocouples? It has miniaturization, small volume, small heat capacity, small thermal inertia, fast response to the measured temperature, and small time constant. The armored thermocouple is a very thin overall combined structure. It is highly flexible and can be bent into various shapes. It is suitable for objects with complex structures. It has good mechanical properties, is strong and reliable, and is resistant to vibration and impact. 53. When using a thermocouple to measure temperature, why is the reference terminal of the thermocouple required to be at 0°C? From the principle of thermocouple temperature measurement, we know that the size of the thermoelectric potential is related to the temperature difference between the two ends of the thermocouple. Therefore, to accurately measure the temperature, the temperature of the reference end must be fixed, usually at 0°C. The reference end of the thermocouple index meter and the temperature meter based on the index scale are both conditioned on 0°C. Therefore, the reference end of the thermocouple is required to be at 0°C during use. If the reference terminal is not 0°C when used, the temperature of the reference terminal must be corrected. 54. What are the specific methods of temperature treatment at the reference end of a thermocouple? Specific methods include: (1) Thermoelectric potential correction method ； (2) Reference end constant temperature method ； (3) Reference end temperature compensation method. 55. What is the compensation wire of a thermocouple? The compensation wire of a thermocouple is actually a pair of thermocouple wires used within a specified temperature range (usually 0 to 100°C). It is made of the same metal material as the thermocouple electrode material or an inexpensive metal material that is easy to obtain and has the same thermoelectric properties as the thermocouple within the specified temperature range. It is used as a connecting wire between the thermocouple and the secondary instrument during temperature measurement. 56. When using thermocouples to measure temperature, why do we need to connect compensation wires? When using a thermocouple to measure temperature, the temperature of the reference terminal of the thermocouple must be kept constant. Because thermocouples are generally made shorter, especially thermocouples made of precious metal materials are shorter. In this way, the reference end of the thermocouple is very close to the object being measured, causing the temperature of the reference end to be high and fluctuate greatly. Therefore, a longer thermocouple should be used to extend the reference end to a place where the temperature is relatively stable. This method is relatively feasible for cheap thermocouples, but is very uneconomical for precious metals and is not convenient for laying thermocouple wires. Considering that the temperature at the reference end of the thermocouple is often below 100°C, the compensation wire has the same temperature-thermoelectric potential relationship as the thermocouple within this temperature range, which can extend the thermocouple, is cheap, and is easy to lay. Therefore, compensation wires must be connected when using thermocouples. 57. What issues should be paid attention to when using compensation wires? 1. The compensation wire must be matched with the corresponding type of thermocouple. 2. When connecting the compensation wire to the thermocouple instrument, the positive and negative poles cannot be connected incorrectly. Both pairs of connection points need to be at the same temperature. 3. The temperature of the compensation wire and thermocouple connection point shall not exceed the specified temperature range. 4. Select the wire diameter of the compensation wire according to the different requirements of the instrument. 58. What is a thermocouple reference end temperature compensator? The thermocouple reference terminal temperature compensator is a device used to automatically compensate for changes in thermocouple measurement values due to changes in reference terminal temperature. In essence, it is a DC signal millivolt generator that can produce a DC signal that changes with the temperature of the reference terminal. When it is connected in series to the thermocouple measurement circuit to measure temperature, the reference end temperature can be automatically compensated. 59. What issues should be paid attention to when using a thermocouple temperature compensator? (1) Various temperature compensators can only be used with corresponding types of thermocouples ； (2) When connecting the temperature compensator to the thermocouple, do not reverse the polarity, otherwise the temperature measurement error will increase. ； (3) Adjust the starting point of the indicating instrument according to the compensation temperature of the compensator ； (4) The compensator must be inspected and calibrated regularly ； (5) Display instruments with automatic compensation mechanisms should not be connected to this reference end temperature compensator. 60. What is the comparative method for thermocouple verification? The comparison method is a calibration method that uses a higher-level standard thermocouple and the thermocouple to be tested to directly compare in the calibration furnace. The standard thermocouple and the thermocouple to be tested are bundled together and sent into the calibration furnace, the measuring end of the thermocouple is placed in a uniform temperature field, and their thermoelectric potential is measured with a testing instrument to obtain the difference between them. 61. What are the contents of the visual inspection before thermocouple calibration? (1) Whether the measuring end is welded firmly, whether the surface is smooth, and whether there are any defects such as pores ； (2) Whether the precious metal thermocouple has fragile defects in the hot electrode, and whether there are serious stains or blackening after cleaning. ； (3) Whether the base metal thermocouple has any defects such as serious corrosion or fragile hot electrode. 62. What are the secondary meters that can be used with thermal resistors to measure temperature? The secondary meters used for temperature measurement matched with thermal resistors mainly include moving coil temperature measuring instruments, ratio thermometers and automatic balancing bridge thermometers. 63. What is the role of temperature transmitter in temperature measurement? The millivolt signal of the thermocouple and the resistance change signal of the thermal resistor are converted into a unified current signal through the temperature transmitter and input into the display and recording instrument. It can be used for automatic detection of temperature and input into the regulator to form an automatic adjustment system for automatic temperature adjustment. After conversion and input into an electronic computer, temperature patrol detection, computer control, etc. can be carried out. 64. What is the temperature measurement principle of radiation pyrometer? The temperature measurement principle of the radiation pyrometer is to use the thermal radiation energy of the object to be measured to have a certain relationship with its temperature, and to display the temperature of the object to be measured by measuring the thermal radiation energy. 65. What types of radiation pyrometers are there? Currently widely used radiation pyrometers include optical pyrometers and total radiation pyrometers. In addition, colorimetric pyrometers, infrared thermometers, etc. are also developing. 66. What is the significance of measuring pressure in thermal power plants? Pressure is an important parameter in thermal processes. Accurately measuring pressure and then controlling pressure is of great significance to ensure the safe and economical operation of thermal equipment. If the main steam pressure is not well controlled, if the steam pressure is too high, the superheater and water wall will not be able to withstand it. If the main steam pressure is too low, the boiler output and the thermal efficiency of the steam turbine will decrease. If the condenser vacuum fails to meet the requirements, the turbine output will decrease and the efficiency will decrease. Affects the safety and economic benefits of the entire unit. 67. What is pressure? Pressure in engineering technology corresponds to pressure in physics. The so-called pressure is the force acting vertically on a unit area. 68. What is absolute pressure? The total pressure in the space where liquids, gases and steam are located is called absolute pressure. 69. What is gauge pressure? The difference between absolute pressure and atmospheric pressure is called gauge pressure. 70. What is negative pressure or vacuum? When the gauge pressure is negative, it is called negative pressure and vacuum. 71. What types of pressure gauges are used in thermal power plants? The pressure measuring devices used in thermal power plants mainly include the following categories:: (1) Liquid column pressure gauge ； (2) Piston type static pressure gauge ； (3) Elastic pressure gauge ； (4) Strain gauge type remote pressure gauge. 72. Briefly describe the pressure measurement principle of liquid column pressure gauge? The principle of liquid statics states that: The static pressure at a point in a liquid is determined by the depth of the point, the weight of the liquid, and the applied pressure. The liquid column pressure gauge measures pressure based on this principle. When the specific gravity of the sealing liquid is constant and the external pressure is constant, the measured pressure is only related to the height of the liquid column of the sealing liquid. The measured pressure can be known by reading the height of the liquid column. 73. For liquid column pressure gauges, what are the commonly used sealing liquids? Commonly used sealing liquids for liquid column pressure gauges include mercury, water, alcohol and carbon tetrachloride. 74. What are the variations of liquid column pressure gauges? (1) Single tube pressure gauge ； (2) Tilt micromanometer ； (3) U-tube pressure gauge ； 75. Briefly describe the working principle of piston pressure gauge? Piston pressure gauges measure pressure based on the force balance principle of hydrostatics and Pascal's theorem. When measuring, one force is generated by the measured pressure, and the other force is generated by the weight placed on the load-bearing plate. When these two forces are balanced, the measured pressure value can be calculated based on the weight of the weight. 76. What components does a piston pressure gauge consist of? The piston pressure gauge consists of a piston, a piston cylinder, a load-bearing plate, a special weight, a gauge joint, an oil cup, a pressure pump and a handwheel. 77. What types of local indicating elastic pressure gauges are used in thermal power plants? The main local indicating elastic pressure gauges commonly used in thermal power plants include: (1) Spring tube pressure gauge ； (2) Diaphragm micromanometer ； (3) Double bellows differential pressure gauge. 78. What components does a single coil spring tube pressure gauge consist of? Single coil spring tube pressure gauge consists of (1) spring tube ； (2) Support ； (3) Shell ； (4) Connector ； (5) Adjustable pin ； (6) Tie rod ； (7) Sector gear ； (8) Pinion ； (9) Pointer ； (10) Hairspring ； (11) Composed of dials, etc. 79. What is the working principle of spring tube pressure gauge? Spring tube, also known as Bourdon tube, is a tube bent into an arc, spiral or S-shape, and is oblate or elliptical. The short axis direction of the cross section is consistent with the radial direction of the tube bending. When the pressure entering the spring tube is higher than the pressure outside the tube, the inner surface area in the short axis direction is larger than that in the long axis direction and the force is greater, so the tube cross section tends to become rounded. That is, the short axis will grow and the long axis will shorten, resulting in elastic deformation. At this time, the free end must move in the direction of straightening of the pipe. The deformation stops when the elastic force caused by deformation and the force caused by pressure are balanced. The displacement generated by the free end drives the amplification mechanism through the lever, causing the pointer to deflect to a certain angle, and the measured pressure value is indicated by the dial. 80. What is a membrane micromanometer? What is its main use? A pressure gauge with a membrane box or a flexible diaphragm as the elastic sensing element is called a diaphragm micromanometer. Due to the small range, thermal power plants are mostly used to measure the pressure and negative pressure of air supply systems, pulverizing systems, furnaces and tail flues. 81. Briefly describe the calibration contents of elastic pressure gauges? The calibration content of the pressure gauge includes: Determine the basic error, variation, zero position of the instrument, the smoothness of the tapping displacement and pointer deflection (whether there is jump, stagnation and jamming). 82. How to select the calibration point of the elastic pressure gauge? The calibration points of elastic pressure gauges should be selected evenly within the measurement range. Except for the zero point, the number of calibration points should be no less than 4 points for pressure gauges and vacuum gauges. For pressure and vacuum (joint) gauges, the pressure part should be no less than 3 points, and the vacuum part should be 1 to 3 points. Verification points generally choose large scale points with numbers. 83. What is the variation of pressure gauge? What is the allowable value of variation for industrial pressure gauges? Variation refers to the difference between the two readings of the pressure gauge after tapping the case at the corresponding calibration points during the pressure increase calibration and pressure reduction calibration. Variation is neither positive nor negative. According to regulations, the variation of industrial pressure gauges shall not exceed the absolute value of the allowable basic error. 84. What are the two adjustment steps for a single-turn spring tube pressure gauge? What is the role of adjusting these two links? (1) Adjust the position of the movable screw of the lever ； (2) Rotate the transmission mechanism to change the angle between the sector gear and the lever. Different transmission ratios can be obtained by adjusting the movable screw of the lever to achieve the purpose of adjusting the linear error of the pressure gauge. Rotating the transmission mechanism and changing the angle between the sector gear and the lever can adjust the nonlinear error of the pressure gauge. 85. What types of displacement transducers are used for remote transmission of displacement of elastic load cells? (1) Inductive displacement transducer ； (2) Differential transformer displacement converter ； (3) Capacitive displacement transducer. 86. Briefly describe the working principle of the differential transformer remote pressure gauge? The differential transformer type remote pressure gauge is a pressure---displacement---inductance---voltage conversion device. An iron core is connected to the free end of the elastic element, and the elastic deformation produced by the spring tube (or membrane diaphragm) after being compressed is used to change the relative position between the iron core and the coil, so that the inductance of the coil changes, thereby converting the signal of pressure change into a signal of change of coil inductance, thereby changing the output voltage of the differential transformer. This voltage signal is sent to the secondary instrument after phase-sensitive rectification, indicating the size of the measured pressure. 87. Briefly describe the working principle of the force balance pressure transmitter? This pressure transmitter works on the force balance principle. The measured pressure is converted into an action force through an elastic sensitive element (spring tube or bellows), causing the balance lever to deflect. The deflection of the lever is converted into a 0-10mA DC current output by the detection amplifier. The current flows into the feedback moving coil in the permanent magnetic field, causing it to generate an electromagnetic feedback force that is balanced with the action force. When the acting force and the feedback force reach dynamic balance, the lever system stops deflecting. The current at this time is the output current of the transmitter, which is proportional to the measured pressure. 88. What is the Hall effect? A piece of semiconductor placed in a magnetic field, if the direction of the magnetic field is perpendicular to the plane of the semiconductor, and a current is passed through the semiconductor in a direction perpendicular to the magnetic field, an electric potential, called Hall potential, will be generated in the semiconductor in a direction perpendicular to the direction of the magnetic field and the direction of the current. This phenomenon is called the Hall effect. 89. Briefly describe the working principle of Hall pressure transmitter? Hall pressure transmitter works based on the Hall effect of semiconductors. Connect the semiconductor chip (also known as Hall chip element) to the free end of the elastic sensitive element, and place it in the magnetic field of the permanent magnet. When the measured pressure is passed into the elastic sensitive element, its free end will be displaced, causing the position of the Hall element in the magnet to change, thereby generating a Hall potential, which reflects the magnitude of the measured pressure. 90. What is fluid? In layman's terms, a fluid is a substance that can flow. Generally, gases, liquids and powdery solids are all fluids. The characteristic of a fluid is that it undergoes continuous deformation until the external force is eliminated. 91. What is flow? Flow is divided into instantaneous flow and cumulative flow. The instantaneous flow rate is the amount of material passing through a certain section of the pipe per unit time. The cumulative flow rate is the mass or volume of fluid flowing through a certain section of the pipe within a certain period of time. 92. Explain the significance of flow measurement in thermal power plants? In the thermal production process, it is necessary to monitor the flow or total amount of water, gas, coal, oil, etc. Its purpose is manifold. For example, the amount of raw coal or fuel oil needs to be measured for economic accounting ； To control combustion, measuring fuel and air quantities is essential ； The feed water flow and steam flow are indispensable for the three-impulse adjustment of the drum water level. ； In addition, the hourly evaporation of the boiler and the feed water flow rate of the feed water pump under rated pressure can be detected to determine whether the equipment is operating under the most economical and safe conditions. 93. What types of flow meters are used in thermal power plants? Commonly used flow meters in thermal power plants include the following types:: (1) Differential pressure flow meter ； (2) Dynamic pressure flow meter ； (3) Constant pressure drop flow meter (also called rotor type) ； (4) Volumetric flow meter ； (5) Target flow meter ； (6) Electromagnetic flowmeter. 94. Briefly describe the working principle of differential pressure flow meter? Differential pressure flow meters measure flow based on the flow throttling principle. A blocking piece with a round hole in the middle and a diameter smaller than the diameter of the pipe is fixed in the round pipe perpendicular to the axis of the pipe, called a throttling piece. When the fluid flows through the throttling member, the flow rate increases and the static pressure decreases, creating a static pressure difference before and after the throttling member. There is a certain functional relationship between this static pressure difference and the average flow velocity or flow rate in the pipe. Use a differential pressure meter to measure the pressure difference before and after the blocking member, and you can indirectly determine the flow rate of the fluid. 95. What is a throttling device? The throttling piece and pressure-taking device, the straight pipe sections before and after the throttling piece, the mounting flange, etc. are collectively referred to as the throttling device. 96. What is a standard throttling device? The so-called standard throttling device refers to international recommended specifications and * * Standard throttling device. Their structural form, scope of application, processing dimensions and requirements, flow formula coefficients and errors, etc., all have uniformly specified technical information. 97. When using a standard throttling device to measure flow, what requirements must be met? When using a standard throttling device to measure flow, the following requirements must be met: (1) The fluid fills the pipe and flows continuously and stably. The fluid should be a single-phase, uniform fluid. Before reaching the throttling member, the flow line of the fluid is parallel to the axis of the pipe, and there is no vortex. ； (2) The pipe through which the fluid to be measured flows should have a circular cross-section and a diameter of not less than 50 mm. ； (3) The standard throttling part should be installed between two straight pipe sections of equal inner diameter. There must be no other local resistance parts within a certain distance before and after the throttling part. 98. What are the advantages and disadvantages of standard orifice plates and standard nozzles? Advantages of orifice plates: It has simple structure, convenient processing, easy installation, material saving and low cost. The disadvantages are that the pressure loss is large, the inlet edge of the orifice plate has poor resistance to fluid corrosion, and it is difficult to ensure sharpness. The error in the expansion coefficient of the orifice plate is also larger than that of the nozzle. Advantages of standard nozzles: It has a large measuring range, requires a short straight pipe section, small pressure loss, low sensitivity to medium erosion during use, wear resistance and long service life. The disadvantages are complex structure, high processing technology requirements and high cost. 99. What is a double bellows differential pressure gauge? What are the characteristics? The double bellows differential pressure meter is a fixedly installed industrial instrument. It can be used in conjunction with a throttling device to measure the flow of fluids, and can also be used to measure differential pressure and liquid level. Its main features are: (1) Mercury-free ； (2) Use welded bellows. Because of its consistent effective area, it can reduce the measurement error caused by general differential pressure gauges working under high pressure. Therefore, it can work under high static pressure conditions ； (3) It has a damping device and adjustable damping time, and can measure pulsating pressure. (4) It has a one-way overload protection device to prevent damage to the sensing element of the instrument due to misoperation. 100. What is the significance of measuring water level in thermal power plants? There are many equipment in thermal power plants that need to maintain normal water levels to operate safely and economically, such as boiler drum water levels, turbine condenser water levels, deaerator water levels, high and low pressure heater water levels, etc. Therefore, accurately measuring the water level, and then better controlling the water level change within the allowable range, is of great significance to ensure safety and improve economic benefits. 101. What types of drum water level gauges are used in thermal power plants? Steam drum water level gauges mainly include mica water level gauges, differential pressure low-mounted water level gauges, electrode water level gauges, and industrial televisions. 102. Briefly describe the measurement principle of mica water level meter and explain its main purpose? The mica water level gauge uses the connector principle to measure water level. It is mainly used to monitor the drum water level when the boiler is started and stopped and to regularly calibrate other types of water level gauges during normal operation. 103. What is a balancing container? What parts does it consist of? “The "water level---differential pressure" conversion device is called a balance container. A simple balance container consists of a positive pressure chamber and a negative pressure chamber. 104. What are the main causes of errors when using a differential pressure water level meter to measure the drum water level? (1) During the measurement process, changes in drum pressure will cause severe changes in saturated water and saturated steam, thus causing errors in differential pressure output. (2) The general design and calculation of the balance vessel compensation pipe is based on the water level being at zero water level. If the boiler drum water level deviates from the zero water level during operation, it will cause measurement errors. (3) When the drum pressure suddenly drops, the condensed water in the positive pressure chamber may be evaporated, causing the instrument indication to be abnormal. 105. How does the two-color water level meter work? The two-color water level meter measures the water level based on the principle of the connector and the principle that steam and water have different refractive index to light. 106. Briefly describe the working principle of the electric contact water level meter? Since there is a huge difference in resistivity between water and steam, saturated steam can be regarded as a non-conductor (or high-resistance conductor), while water can be regarded as a conductor (or low-resistance conductor). The electric contact water level meter uses this principle to determine the position of the soda-water interface by measuring the resistance between the electrodes in the soda-water medium in the measuring cylinder connected to the container. 107. What are the advantages and disadvantages of electric contact water level gauge? The advantages of the electric contact water level meter are that it can adapt to the variable parameter operation of the boiler, has small delay, simple structure, intuitive display, low cost, and easy maintenance. Its main disadvantage is that the electrode is immersed in water for a long time, which easily causes corrosion and leakage, as well as the fixed error caused by discontinuity in the display. 108. What is the significance of measuring the oxygen content of boiler flue gas? The combustion quality of the boiler directly affects the coal consumption of the power plant. When the boiler is in the best combustion state, it has a certain excess air coefficient a, and a has a certain relationship with the O2 content in the flue gas. Therefore, the O2 content in the flue gas can be monitored to understand the value a to determine whether the combustion is in the optimal state. The O2 content signal can even be introduced into the combustion automatic control system as a correction signal to control the air supply volume to ensure economical combustion of the boiler. 109. Briefly describe the measurement principle of magnetic oxygen meter? The magnetic oxygen meter utilizes the thermomagnetic characteristics that the magnetic susceptibility of oxygen in each component of the flue gas is much higher than that of other gases, and its magnetic susceptibility decreases rapidly as the temperature increases. It forms a magnetic wind in the transmitter. The transmitter converts the size of the magnetic wind into a change in the resistance of the resistor. By measuring this resistance, the O2 content can be known. 110. Briefly describe the measurement principle of zirconia oxygen meter? The zirconia oxygen meter uses a zirconia solid electrolyte as a sensor. Porous metal platinum electrodes are attached to both sides of the zirconia solid electrolyte to expose it to high temperatures. When the oxygen concentration in the gas on both sides is different, a potential is generated between the electrodes, which is called the oxygen concentration difference potential. When the temperature is constant, this potential is only related to the oxygen content in the gas on both sides. By measuring this potential, the oxygen content can be measured. 111. What are the advantages of zirconia oxygen meter compared with thermal magnetic oxygen meter? The zirconia oxygen meter has the incomparable advantages of a magnetic oxygen meter such as simple structure, rapid response and low maintenance workload. Due to the small time delay, it can be used as a correction signal for boiler combustion regulation. 112. What are the monitoring projects for large steam turbines? Monitoring items for large steam turbines include cylinder metal temperature, bearing vibration, axial displacement, large shaft eccentricity, differential expansion of high and low pressure cylinders, shell expansion, turbine speed and valve opening, etc. 113. Briefly describe the working principle of the electrical tachometer? The electrical tachometer uses a tachometer generator as the converter. The tachogenerator is connected to the turbine shaft through a flexible shaft. When the steam turbine rotates, it drives the tachogenerator rotor to rotate, thereby generating electricity. Its output voltage is proportional to the rotation speed. The AC voltage output by the tachometer generator is rectified into a DC voltage by each set of rectifiers, and is added to each voltage divider. The voltage signal taken out by the voltage divider is sent to the display meter to indicate the speed. 114. Briefly describe the working principle of SS-46 two-way vibration meter. The SS-46 two-way vibration meter consists of a vibration pickup, an integrating amplifier and a display instrument. When the object being measured vibrates, the air gap in the constant magnetic field formed between the magnetic steel and the magnet conductive body in the vibration pickup placed on the object vibrates accordingly. The induced potential in the air gap is in a relatively static state. After being integrated by the integrating amplifier, this potential becomes a voltage signal proportional to the vibration amplitude. After amplification, detection, and filtering, a DC voltage signal corresponding to the vibration amplitude is output and sent to the indicator meter to obtain the magnitude of the vibration. 115. Briefly describe the working principle of electronic orbital scale? Electronic track scale is a kind of dynamic automatic weighing equipment for trains. It can be used for attached dynamic weighing, unattached slide-out dynamic weighing, and can also be used as static weighing equipment. When the train passes through the table, the table is stressed, and the sensor converts the weight signal into a voltage signal and sends it to the analog channel. After amplification, filtering, and analog-to-digital conversion, it enters the microcomputer. At the same time, the wheel signal also enters the switch channel, and after shaping, is sent to the microcomputer. When the entire system is working, the computer performs sampling and data processing on the front and rear bogies of the carriage, thereby obtaining the weight value of a carriage for screen display, printing and tabulation, etc.