Common problems and solutions of differential pressure flowmeter
1. After the system is put into operation, the differential pressure flowmeter has no flow display
Check that the differential pressure flowmeter is switched on and there is still no flow displayed on the screen or it is displayed as zero after the exhaust is fully exhausted. Observe the flow fluctuation and measure the output current of the instrument through the exhaust process. After eliminating the possibility of instrument damage, check the process conditions, positive and negative Check the layout of the instrument pipeline on the pressure side and the installation of the orifice plate to confirm the cause of the failure.
(1) Check the wiring and settings of the differential pressure flowmeter instrument, fully exhaust and put the instrument into operation;
(2) Contact the commissioning system engineer to check and confirm the valve status once;
(3) Verify that the instrument pipelines on the positive and negative pressure sides of the differential pressure flowmeter are connected correctly;
(4) Check whether the throttle orifice is installed backwards.
2. The flow rate of the differential pressure flowmeter is low
During the pump flow test during the cold test, it was found that the measured value of the online differential pressure orifice meter was different from the measured value of the on-site portable flow meter. After comparing with the characteristic curve of the pump, it was judged that the measured value of the differential pressure meter was inaccurate. By checking the instrumentation and logic settings, on-site exchange of other channel instruments for testing, the reasons are summarized as follows:
(1) The square root is not set on the meter. According to the characteristics of the orifice plate differential pressure flowmeter, the flow rate is proportional to the square root of the orifice plate differential pressure. The differential pressure value measured by the pressure-sensing element of the differential pressure meter needs to be square rooted before it can be converted into a screen display value. If the square root is not used, the screen display value will be too small. Some smart meters can set the square root in the meter, while some can only set the square root in the logic.
(2) The calculated value of the orifice plate is inconsistent with the calibration value of the meter. Due to the differential pressure between the calculation sheet provided by the design institute and the maximum flow rate of the process design, the measurement of the instrument calibrated according to the standard differential pressure of the orifice plate is inaccurate. By verifying the maximum flow rate of the orifice plate calculation sheet and the process design, sort out the list of orifice plate differential pressure flowmeters with inconsistent designs, calculate the corresponding differential pressure value under the maximum flow condition, and use this differential pressure value as the maximum difference measured by the instrument Check the instrument again, and the flow rate of the put into operation test is normal.
