How to reset the pressure transmitter when it is used?
1. Purpose of the operation: Due to the measurement of the pressure transmitter, it is necessary to re-check the zero return.
2. Job content: Perform zero return check adjustment on the pressure transmitter.
3. Operation requirements: Due to factors such as the use of environment, medium, isolation fluid or instrumentation components, the pressure transmitter is inaccurate in zero measurement, and the transmitter needs to be checked for zero return.
4. Job preparation and hazard identification
4.1, the operator's process, according to the instrument circuit and the operation category to open the corresponding work ticket, and implement the safety measures required by the work ticket; carry out hazard identification, do a good JHA analysis.
4.2. The pressure transmitter must be connected to the bucket when discharging the sewage. Pay attention to the nearby high-temperature equipment and pipelines. It is strictly forbidden to discharge anywhere.
4. 3. The operator carries the corresponding tools. If it is a smart transmitter, it must be equipped with a corresponding handheld terminal.
5, the operation method:
5. 1. Classification by transmitter performance:
5.1.1 Analog Transmitter: When the transmitter is in the zero position, adjust the external zero adjustment screw (ZERO) of the transmitter.
5.1.2 Smart Transmitter: The zero point of the smart transmitter can be adjusted on the handheld terminal or on the ZERO of the watch body. The external adjustment can be divided into three types. One can be adjusted on the ZERO screw on the watch body. If the ZERO adjustment screw on the watch body is to be used, the external adjustment screw in the handheld terminal is set to permit, for example, Fuji FCX series, horizontal River EJA and so on. One is to use a magnetic bar or button to return to zero at the ZERO position on the body, such as Honeywell ST3000, Rosemount 3051, and so on. One is that you must first press and hold the ZEROSPAN button 5S to activate, and then press the ZERO button to return to zero, such as 3151 smart transmitter.
5.2, according to the type of transmitter:
5.2.1 Differential pressure transmitter (excluding double flange):
a) For measuring light medium or gas flow, the traditional three-valve (secondary valve) zero return mode can be used to close the positive and negative pressure secondary valves and open the balancing valve for zero return. However, it should be noted that sometimes the light medium will carry bubbles or the gas will bring the liquid to cause the meter to be inaccurate. The meter should be vented or drained before returning to zero.
b) When measuring the steam flow, the positive and negative pressure pipes should be filled with condensate. When the instrument is put into operation, close the positive and negative valves and open the positive and negative vent valves to return to zero. If the positive and negative pressure pipes are not filled with condensate at this time, first close the positive and negative primary valves, open the positive and negative pressure secondary valves and balance valve, open the positive and negative upper venting valves to balance the condensate on both sides of the pressure tube. Then perform the above zero return.
c) When measuring the flow rate of the medium, the meter is filled with the isolation fluid. When the instrument is put into operation, the positive and negative primary valves should be closed, and the positive and negative vent valves should be opened for zero return.
d) For the differential pressure transmitter that needs to migrate the liquid level or differential pressure, the positive and negative one-time valve should be closed. Under the premise of filling the isolation liquid, the balance valve of the three-valve group is closed, and the positive and negative pressure valves are opened. The negative vent valve opens and the migration (adjust the output to zero) adjustment.
5.2.2 Pressure transmitter:
a) When measuring the light medium or gas pressure, close the secondary valve and open the instrument plug to return to zero.
b) When measuring the pressure of the medium, the meter is filled with the isolation fluid. When the instrument is used, the valve should be closed and the upper vent valve should be opened for zero return.
c) When the absolute pressure transmitter returns to zero, it should be adjusted to the value of the transmitter at 100KPa. For example, the range of the transmitter is 0-200KPa, and it should be adjusted to 50% when returning to zero.
5.2.3 Single flange liquid level transmitter zero return operation:
a) Single flange transmitter: When measuring the liquid level of the open container with a single flange transmitter, if the installation position of the transmitter is higher than the low liquid level of the container, adjust with zero negative migration; if it is lower than When the container's zui low liquid level, it is adjusted with zero positive migration by closing the primary valve and opening the upper vent valve for adjustment.
b) Double flange transmitter: When measuring the liquid level of the closed container with a double flange transmitter, regardless of whether the transmitter is installed above or below the two flange bellows, or in two flange bellows In the middle, the transmitter must perform a zero-point negative migration adjustment by closing the positive and negative primary valves, opening the positive and negative upper vent valves, and performing the migration (adjusting the output to zero). When measuring the pipeline flow with a double flange transmitter, there is generally no migration. The positive and negative primary valves should be closed, and the positive and negative vent valves should be opened for zero return.
5.2.4 Absolute pressure transmitter
Absolute pressure transmitter calibration steps:
Make a 4-20 mA trim to correct the D/A converter inside the transmitter.
Perform a full fine-tuning to match the 4-20 mA, digital reading to the actual applied pressure signal, thus requiring a source of pressure.
Finally, the heavy-quantity process is performed, and the analog output 4-20 mA is matched with the applied pressure signal source by the adjustment, and the action is exactly the same as the zero-setting (Z) and the range-adjusting (R) switch on the transmitter casing.
6, inspection and acceptance:
6.1. After the meter operator finishes work, the work content should be confirmed. After the process is confirmed to be in normal operation, the work ticket is signed.
6.2 After the completion of the operation, the site should be cleared after the completion of the work.
7. Requirements and precautions when using the instrument
7.1. For the differential pressure transmitter that needs to migrate when measuring the liquid level or differential pressure, it is forbidden to open the balance valve of the three-valve group under the premise of filling the isolation liquid. It is also prohibited to open the balance valve of the three-valve for the differential pressure transmitter that is filled with the flow of the isolation liquid.
7.2. The instrument pressure piping, valves and joints shall not leak after being discharged.