Instrument Technician Exam Questions

This post was last edited by cnooczhouyx on 2011-9-28 at 11:31. I. True or False Questions (2 points per question, 20 points in total) 1. A static pressure level gauge operates on the principle that as the liquid level changes, the static pressure at a certain point at the bottom or side of the container also changes accordingly. Answer: √ 2. When calibrating the float level gauge, connect a plastic tube to the bottom of the float chamber; the verticality of the plastic tube does not affect the accuracy of the calibration. Answer: √ 3. In a constant buoyancy type level gauge, the float remains always floating on top of the medium, and its displacement changes in a 1:1 ratio as the liquid level changes. Answer: √ 4. When using a single-flange level gauge to measure the liquid level in an open container, the range of the gauge refers to the increase in pressure on the level gauge as the liquid level rises from its lowest point to its highest point. Answer: √ 5. The thermoelectromotive forces of thermocouples A and B are independent of the intermediate temperature of materials A and B, and depend only on the temperatures at the cold and hot ends, T1 and T0. Answer: √ 6. A differential pressure flow meter measures flow by utilizing the pressure difference generated as fluid passes through a throttling element. √ 7. When the medium to be regulated contains solid suspensions, a control valve with quick-opening characteristics is advisable. Answer: × When the medium to be regulated contains solid suspensions, a control valve with linear characteristics is advisable. 8. When tuning the parameters of a cascade control system, the main loop should be tuned first, followed by the secondary loop. Answer: × 9. The protective grounding must be firm and reliable; it can be connected to the electrical protective grounding network, but grounding in series is not allowed. ( √ ) 10. The maximum pressure measured by a pressure gauge generally should not exceed 2/3 of the gauge’s upper measurement limit. ( √ ) II. Multiple-choice fill-in-the-blanks (2 points per blank, 30 points in total) 1. 1 pascal is the pressure resulting from a force of 1 newton acting on an area of ( ). (A) 1m2 (B) 2m2 (C) 0.01m2 (D) 0.1m2 Answer: A 2. A thermistor is made of metallic materials with （） properties. (A) One (B) Two (C) Three (D) Three or more. Answer: A. 3. The minimum reading that a typical Bourdon tube pressure gauge can display must not be lower than ( ) of its maximum measurement range. (A) 2/3 (B) 1/3 (C) 1/4 (D) 1/2 Answer: B 4. The function of the diaphragm in a pressure transducer’s sensing element is to convert （ ） into a concentrated force. (A) Differential pressure to be measured (B) Pressure signal (C) Pressure of the medium being measured (D) System pressure. Answer: C. 5. The control principle of a solenoid valve belongs to ( ). (A) Proportional control (B) On-off control (C) Integral control (D) Differential control Answer: B 6. When using a float level gauge to measure the liquid level, if the float falls off, what will be the output signal of the gauge? (A) Minimum (B) Maximum (C) Zeroing (D) Unchanged. Answer: B. 7. In automatic control systems, the type of control that can be applied independently is ( ) control. (A) Differentiation (B) Integration (C) Proportionality (D) Integral differentiation Answer: C 8. The correct procedure for shutting down a differential pressure transmitter is ( ). (A) First, close the positive and negative pressure hand valves of the three-valve assembly, open the balance hand valve, and then close the pressure tapping hand valve. (B) First, close the pressure tapping hand valve, then close the positive and negative pressure hand valves of the three-valve assembly, and open the balance valve. (C) First, close the pressure tapping hand valve, then open the balance valve, and close the positive and negative pressure hand valves. (D) First, open the balance valve, then close the positive and negative pressure hand valves, and finally close the pressure tapping hand valve. Answer: A. 9. The minimum flow rate that can pass through a throttle orifice flow meter is not less than ( ) of the full scale. (A) 10% (B) 30% (C) 20% (D) 5%. Answer: B. 10. Which of the following statements about bimetallic thermometers is incorrect? (A) A bimetallic strip is composed of two layers of metals with different coefficients of expansion. (B) The scale of a bimetallic thermometer is generally clearer than that of a mercury thermometer. (C) Bimetallic thermometers are resistant to vibration. (D) The layer with the higher expansion coefficient bends toward the layer with the lower expansion coefficient. Answer B: 11. Which of the following statements about flanged transmitters and ordinary differential pressure transmitters is incorrect? ( ) (A) Flanged transmitters respond more slowly than differential pressure transmitters. (B) Flanged transmitters have lower sensitivity than differential pressure transmitters. (C) The measurement range of flanged differential pressure transmitters is limited by the length of the capillary tube. (D) Flanged transmitters are easier to repair than ordinary differential pressure transmitters. Answer D: 12. When sizing a control valve, the diameter of the valve is primarily determined based on its ( ). (A) Normal flow rate (B) Pipe diameter (C) Flow capacity (D) Fluid viscosity. Answer: C. 13. For a gas-operated single-seat valve that is in operation, operators report high leakage rates; this is usually caused by the following reasons, but one of them is incorrect – which one? (A) Severe wear of the valve core and seat. (B) Air leakage in the actuator diaphragm of the control valve. (C) The valve stem is too long. (D) Excessive pressure difference before and after the control valve. Answer: C. 14. The pressure of the heating steam generally should not exceed ( ) MPa. A.O. 5MPa ； B．1. 0MPa ； C. 1.5MPa ； D. 2.0 MPa Answer: B 15. For the grounding system of a DCS, its grounding resistance should be less than ( ). A. 4Ω ； B. 6Ω ； C 7Ω ； D. 1Ω Answer: A III. Fill in the blanks (2 points per blank, 20 points in total) 1. Without temperature compensation, the voltage corresponding to 100°C for a K-type thermocouple is (4.096) MV, while the voltage corresponding to 100°C for an E-type thermocouple is (6.319) MV. 2. If the resistance measured by a PT100 sensor is 123.24Ω, then the corresponding temperature is (60) °C. 3. In physics, the level of a fluid is represented by (L). 4. The flow rate of a fluid is in a (square root) relationship with its pressure. 5. 5.250 Pa = (25) mmH2O. 6. The displacement alarm setting for the coking rich gas compressor is (0.5) mm, while the interlock value is (0.7) mm. 7. The flap level gauge should be installed (vertically); valves should be installed between the container and the equipment to facilitate maintenance and adjustment of the instrument. IV. Calculation problems (7, 7, 8, 8) 1. Use the water calibration method to calibrate an electric float level transmitter. Given that the length of the float is L = 500 mm and the density of the medium being measured is 0.85 g/cm3, calculate the height by which the float needs to be submerged in water when the output is at 0%, 50%, and 100% (the density of water is taken as 1 g/cm3). 2. What is the function of an anti-surge valve? And the mode of action? 3. Describe the operation steps for the initial startup of a differential pressure transmitter used to measure steam flow, including checking whether all valves, pressure guiding pipes, union joints, etc., are properly connected ； 2) Check whether the secondary valve and the drain valve are closed, and whether the balance valve is open ； 3) Open the valve slightly once, then check the pressure guide tube, valve, union, etc.; if there is no leakage, open the valve fully ； 4) Open the drain valves separately, discharge the waste fluid, and then close the drain valves ； 5) Loosen the screw plug in the differential pressure chamber to release the air inside ； 6) The differential pressure transmitter can be activated only after the pressure guiding pipe is filled with condensed water ； 7) To start the differential pressure transducer, it should be done in the order of opening the positive pressure valve, closing the balance valve, and opening the negative pressure valve. 4. There is a pneumatic differential pressure transmitter with a measurement range of 25,000 Pa; the corresponding maximum flow rate is 50 t/h. The process requirement is that an alarm be triggered at a flow rate of 40 t/h. Question: (1) What is the alarm value in Pa when no square root calculator is used? (2) When a square root calculator is used, what should the alarm value be set at in Pa? Solution: 1. Without a square root calculator, the differential pressure corresponding to a flow rate of 40 t/h is ΔP1 = 25000 × (40/50)² = 16000 Pa. With a square root calculator, since ΔQ = K × ΔP, the differential pressure for a flow rate of 40 t/h is ΔP2 = 25000 × (40/50) = 20000 Pa