How to analyze fault of smart pressure transmitter
Usually , we analyze fault of smart pressure transmitter as below :
The Smart pressure transmitter use in the petrochemical unit and the output signal is connected via a cable
to the DCS system and the operator monitors the device field pressure through the DCS system operator
station. In the event of a malfunction of the intelligent pressure transmitter, the DCS operator station will display
a high or low measured value or a measurement loop IOP(-) alarm. When dealing with a fault, it is first necessary
to judge whether it is a fault of the field instrument or a fault of the DCS system. If it is a field instrument failure,
then it is necessary to conduct a comprehensive analysis of the actual failure of the instrument, and according to the characteristics of the instrument used, take corresponding measures for processing; if the failure detection result
shows that the DCS system is faulty, system maintenance is required. Staff coordination.
Solve the fault of smart pressure transmitter :
1) The pump outlet pressure value is too high.
Fault phenomenon: The pump outlet pressure of a chemical plant in
a chemical company, the process operator reflects that the pressure display value in the DCS system is 0.15 MPA
higher than the on-site pressure gauge. The display value on the DCS system is 0.15 MPa higher than the display
value on the LCD screen of the on-site meter.
Fault handling: The instrument maintenance personnel first went to the site to confirm that the LCD display value
of the transmitter's on-site meter head was the same as that displayed on the process site pressure gauge, but
the DCS system showed a value higher than 0.15 MPa. The standard current signal is output at the scene, and the
displayed value in the test DCS system is normal, so it is judged that the fault occurs in the field instrument. Through
the hand-held device of the intelligent pressure transmitter, it is found that the measured value is the same as the
display value of the transmitter head. The output current is calculated from the measured value and the measured
range, and the calculated current value is found to be lower than the actual output value, so the fault occurs on the
transmitter output circuit. After replacing the transmitter output circuit board, re-calibrate the pressure transmitter,
and the pressure display in the DCS system returns to normal.
2). The fuel gas pressure value is low
Fault phenomenon: The fuel gas pressure is sent to the SIS system through the three-selection two mode for interlock protection, and the pressure signal is displayed in the DCS system through communication. The device operator reported
that one pressure transmitter showed a low value.
Fault handling: When the fault is processed on site, it is found that the on-site display of the faulty transmitter is the same as the displayed value in the DCS system, indicating that there is a problem with the field instrument, and the pressure has a relatively stable deviation, so during the processing Three conditions can be considered: the first is the on-site pressure line, the second is the transmitter damage, and the third is the zero drift. A part of the liquid was found on the discharge lead, and the three pressure transmitters displayed the same value after discharge.
3). Fine tower top pressure no display failure
Fault phenomenon: The operator reflects that the pressure at the top of a fine tower is not displayed.
Fault handling: The instrument maintenance personnel first check the DCS operation station and find that the pressure control circuit displays IOP- (ie, the signal received by the DCS system is lower than 4 mA), indicating that the pressure measurement circuit may have an open or short circuit fault. Check the field wiring measurement of the DCS control cabinet. The fuse terminal light of the terminal block lights up, and the test result shows that the fuse has been blown. After the insurance is replaced, the pressure measurement is normal, and the fuse is blown after a period of time. This indicates a short circuit or ground fault in the measuring line. Remove the field wiring of the control cabinet, ground the positive and negative wiring with a multimeter, and find that the negative terminal is short-circuited to the ground, indicating that the negative terminal wiring is grounded. By checking the main cable and the branch cable, it was found that the line of the branch cable entering the main cable junction box was damaged, and the pressure was normal after processing.
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