【Daily Question 20090412】Discussion on analytical instruments

Instrument manufacturer: Swiss company MBW. Principle of operation: optical subcooling mirror principle. Components analyzed: on-site measurement of gases in high-pressure, large-capacity sulfur hexafluoride (SF6) switchgear. Problems that occur during use (as important answers): When using the DP19 dew point meter to test the 110KV GIS CT in a certain substation, with the same instrument, the moisture content in most gas chambers was within acceptable limits; however, in three gas chambers, despite multiple vacuuming and nitrogen filling operations carried out by the installation team and the manufacturer, the test results still showed **excessive moisture levels**. Through various studies and research, it was found that if impurities in the gas sample exist in vapor form, such as hydrocarbons, they must condense before water vapor condenses, which directly affects the gas dew point measurement. Experience of use: The DP19 dew point meter has advantages such as easy testing, fast speed, low gas consumption, and high accuracy. However, impurities such as hydrocarbons in vapor form can significantly affect the test results; it is necessary to take measures to remove moisture before testing.

Instrument manufacturer: Mettler Toledo. Principle of operation: Electrolysis. Analyzed component: pH. Problems that occur during use (as important answers): It is common for the indicated value to deviate from the actual value; it is necessary to clean and calibrate the instrument regularly during use

Instrument manufacturer: Shifu Mei. Instrument principle: Paramagnetic oxygen analyzer, infrared gas analyzer. Analyzed components: O2, CO2, C3H6. Problems that occur during use (as an important point to address): It is crucial to carry out regular maintenance of the sample preprocessing equipment during routine inspections, to ensure that the sample gas meets the requirements for measurement by the instrument, thus ensuring its proper operation

Instrument manufacturer: Yokogawa Corporation. Instrument name: ZR402G Separate Zirconia Oxygen Analyzer. Purpose of the instrument: The EXAxt ZR separate zirconia oxygen analyzer is an analytical device used to monitor and control the oxygen concentration in combustion gases, boilers, and industrial furnaces. Analyzed components: O2 and CO2 levels. Working principle: Electrolysis. Causes of failures and solutions: Fault symptom: Occasional display of cold-end temperature alarm on the panel； Cause analysis: (1) The cold junction connection signal wire between the transmitter and the probe is damaged, or the cable is not properly connected to the terminal blocks. (2) The positive and negative poles of the cold-end signal connection wire are short-circuited at the extension or connection terminals. (3) The cold-end temperature sensor located on the probe wiring board has failed. (4) Fault in the electronic circuit inside the transmitter. Solution: Check according to the operation manual whether the probe terminal block temperature is within the specified range. The temperature range of the probe varies depending on the type of probe. If the probe wiring board is outside the temperature range, take measures to lower the temperature, such as changing its position so that it is no longer exposed to heat radiation.

Instrument manufacturer: Tianjin Haixiangzi Automatic Control Equipment Co., Ltd. Instrument name: NQD-2200 intelligent pour point online analyzer. Purpose of the instrument: An explosion-proof online quality analyzer specifically designed for the continuous and automatic analysis of the freezing point of diesel during oil refining processes. Analyzed component: Diesel. Working principle: It is an electromagnetic pressure pulse-based method for testing the freezing point of oils online; during testing, the sample oil in the cold core testing chamber is cooled, thereby reducing its temperature. At the same time, a voltage is applied to the electromagnetic coil of the electromagnetic pulse generator, causing a cylindrical magnetic conductor to rise and thus reducing the pressure in the pipeline above the cold core testing chamber. A pressure detector measures the change in pressure, while a temperature-sensing platinum resistor in the cold core testing chamber detects the decrease in temperature. This process is repeated until the pressure drops to a critical value, at which point the temperature of the sample oil corresponds to its freezing point. This method offers extremely high reliability and stability in testing. Cause of the fault and solution: Fault symptom: The DCS reading remains unchanged for an extended period or fluctuates significantly, exceeding the normal range (it does not show a linear relationship with the data provided by laboratory analyses). Cause analysis: 1. The on-site instruments indicated an alarm for the differential pressure at the sample inlet and outlet. 2. The distance between the sampling point and the analyzer is large, the tubes are thin, and diesel contains many impurities, which often leads to blockages. 3. Due to funding constraints, the accompanying preprocessing system was removed. Solution: 1. Reduce the distance between the sampling point and the analyzer, and move the sampling point to the pump outlet that is closer to the analyzer. 2. Clean the filter regularly (now it is changed to once a week). 3. Application fee: The filtration system shall be included as per the design requirements.

Instrument manufacturer: Shanghai Youke Jiawa. Instrument name: Humidity meter. Principle of operation: Capacitive. Analyzed component: Cold air before heating in the hot air furnace. Problems that occur during use: The humidity value cannot be measured accurately; the humidity changes as the temperature inside the cabinet changes and as the gas flow rate varies

Instrument manufacturer: Beijing Aikuirun Technology Co., Ltd. (TELEDYNE online gas analysis instruments) Instrument names: Trace oxygen/Concentrated oxygen>Infrared analyzer/Ultraviolet analyzer,Thermocouple analyzer>Total hydrocarbon analyzer>Zirconia analyzer>Total sulfur analyzer/System integration. Principles: Electrochemical,magnetic oxygen detection,Infrared,Ultraviolet,FID. Analyzed components: All gases for online analysis. Issue: The quality of preprocessing has a direct impact on the performance of the instrument

Instrument manufacturer: Beijing Lida Kexin Environmental Safety Technology Co., Ltd. Instrument name: COD online monitor. Working principle: A low-pressure mercury lamp is used as the ultraviolet light source; the ultraviolet light emitted is separated into 254nm ultraviolet light and 546nm visible light using a filter. Dual-wavelength spectroscopy is employed, with a photometer serving as the reference wavelength. The light intensity is detected by diodes, and the resulting signal is sent to a microprocessor via an amplifier. The light intensity at 546nm is used to compensate for the effects of turbidity, and the measurement results are generated after calculation. Analyzed components: Rainwater and sewage. Problems that occur during use: Since rainwater and sewage sometimes contain sediment, it enters the measuring cylinder and contaminates the lenses, affecting the accuracy of measurements; therefore, regular cleaning is required, which results in high maintenance costs

Instrument manufacturer: Xi’an Jueneng Instruments Co., Ltd. Instrument names: Oxygen analyzer, thermal conductivity analyzer, infrared analyzer, dew point analyzer, etc. Principles of operation: Electrochemical, magnetic oxygen, infrared, zirconia. Components analyzed: Oxygen, flue gas, dew point, CO, SO2. Issue: The sampling point must be kept dry, and there should be a dedicated area for analyzing instruments on site. Generally, there are no problems with the sensors; it’s just that some components related to pre-treatment need to be replaced regularly!