Pressure transmitter: 8 types of 24 fault analysis and solutions!

First, the transmitter has no output

Inspection and testing

1. Check if the transmitter power supply is reversed;
2. Measure the power supply of the transmitter, whether there is 24V DC voltage;
3. If it is with a meter, check whether the meter head is damaged (you can short-circuit the two wires of the meter head first. If it is normal after short circuit, it means that the meter head is damaged);
4. Connect the ammeter to the 24V power supply circuit to check if the current is normal.
5. Whether the power supply is connected to the power input of the transmitter;

Solution

1. Connect the power supply polarity correctly.
2. It must be ensured that the power supply voltage to the transmitter is ≥12V (ie, the transmitter power input terminal voltage is ≥12V).
3. If there is no power supply, check whether the circuit is disconnected and the instrument is selected incorrectly (the input impedance should be ≤250Ω);
4. If the meter is damaged, you need to change the meter. If it is normal, the transmitter is normal. At this time, check whether other instruments in the loop are normal.
5. Connect the power cord to the power terminal block.

Second, the transmitter output ≥ 20mA

Inspection and testing

1. Is the transmitter power supply normal?
2. Whether the actual pressure exceeds the selected range of the pressure transmitter;
3. Whether the pressure sensor is damaged or not, the severe overload sometimes damages the isolation diaphragm.
4. Is the wiring loose?
5. Is the power cord wiring correct?

Solution

1. If the transmitter power supply is less than 12VDC, check whether there is a large load in the circuit. The input impedance of the transmitter load should meet RL≤(transmitter supply voltage -12V)/( 0.02A) Ω
2. Re-select the pressure transmitter of the appropriate range.
3. If the pressure sensor is damaged, it must be sent back to the manufacturer for repair.
4. Connect the wires and tighten them.
5. The power cord should be connected to the corresponding terminal.

Third, the transmitter output ≤ 4mA

Inspection and testing

1. Is the transmitter power supply normal?
2. Whether the actual pressure exceeds the selected range of the pressure transmitter;
3. Whether the pressure sensor is damaged or not, the severe overload sometimes damages the isolation diaphragm.

Solution

1. If the transmitter power supply is less than 12VDC, check whether there is a large load in the circuit. The input impedance of the transmitter load should meet RL≤(transmitter supply voltage -12V)/(0.02A) Ω.
2. Re-select the pressure transmitter of the appropriate range.
3. If the pressure sensor is damaged, it needs to be sent back to the manufacturer for repair.

Fourth, the pressure indication is incorrect

Inspection and testing

1. Is the transmitter power supply normal?
2. Is the pressure value of the reference correct?
3. Is the pressure indicating meter's range consistent with the pressure transmitter's range?
4. Is the pressure indicating the input of the meter and the corresponding wiring correct?
5. The input impedance of the transmitter load should be in accordance with RL ≤ (transmitter supply voltage -12V) / ( 0.02A) Ω
6. Whether the input end is open when the multi-point paper recorder is not recorded;
7. Is the corresponding device housing grounded?
8. Is it separate from the AC power supply and other power supplies?
9. Whether the pressure sensor is damaged or not, the severe overload sometimes damages the isolation diaphragm.
10. Whether there are sand, impurities, etc. blocking the pipeline in the pipeline, and the measurement accuracy will be affected when there are impurities;
11. Whether the temperature of the pipeline is too high, the operating temperature of the pressure sensor is -25~85 °C, but it is better to be within -20~70 °C in actual use.

Solution

1. If the transmitter power supply is less than 12VDC, check whether there is a large load in the circuit. The input impedance of the transmitter load should meet RL≤(transmitter supply voltage -12V)/(0.02A) Ω.
2. If the accuracy of the reference pressure gauge is low, it is necessary to replace the pressure gauge with higher precision.
3. The range of the pressure indicating instrument must be consistent with the range of the pressure transmitter.
4. The input of the pressure indicating instrument is 4~20mA, then the output signal of the transmitter can be directly connected; if the input of the pressure indicating instrument is 1~5V, the input of the pressure indicating instrument must be connected with an accuracy of one thousand. One or more resistors with a resistance of 250Ω are then connected to the input of the transmitter.
5, the input impedance of the transmitter load should meet RL ≤, if it does not meet, according to its different measures can be taken: such as raising the supply voltage (but must be lower than 36VDC), reducing the load.
6. If the multi-point paper recorder is not recording, if the input terminal is open: 1, can not carry other loads; 2. Use other recorders with input impedance ≤250Ω when no recording is used.
7. The corresponding device housing is grounded.
8. Separate the wiring from AC power and other power sources.
9. If the pressure sensor is damaged, it needs to be sent back to the manufacturer for repair.
10. When there are sand, impurities, etc. blocking the pipeline in the pipeline, it is necessary to clean up the impurities and add a filter before the pressure interface.
11. The temperature of the pipeline is too high. Add buffer tube to dissipate heat. It is best to add some cold water in the buffer tube before use to prevent the superheated steam from directly impacting the sensor, thereby damaging the sensor or reducing the service life.

In addition to the above faults, pressure transmitters are prone to the following failures:

Five, the installation problem

In steam flow measurement, steam mainly involves two types, one is external steam, and the other is superheated steam of the boiler. The external steam supply is steam after desuperheating and decompression, the temperature is not high, and it is mixed with a large amount of water, and it is not needed when needed, and the steam flow rate is changed according to the requirements of the user. In the actual flow measurement process, sometimes the flow rate is too large, sometimes the flow rate is too small, very unstable, and it is often necessary to carry out sewage discharge. The measurement of the transmitter is accurate after each discharge, but the number of discharges of the steam pipe is increased, and it is easy to cause Each joint on the pressure guiding tube leaks steam.

In the measurement of superheated steam, the biggest problem was that it sometimes stopped. After the restart, the flow will be deviated, resulting in misalignment, and sometimes there is still a little flow after the stop. Generally, the transmitter is installed at a lower position than the measuring pipe. However, in the actual installation, the condensing tank and the transmitter for the external steam flow are higher than the measuring pipeline, and the pressure guiding pipeline which is discharged from the throttle device and laid down at least 1 meter is too short.

The superheated steam flow rate of the boiler also has a problem of inconsistency in the height of the condensing tank and the measuring pipe, resulting in a height imbalance of the condensed water, causing a static pressure difference.

Sixth, the pressure tube is blocked

In pressure measurement, sometimes the indicated pressure does not change with operating conditions. After opening the drain valve, there is only a small amount of sewage and no water flows out. This is because a small amount of floating dust is present in the water or compressed air, and it enters the pressure guiding tube to precipitate with the water flow. Over time, the pipe wall of the pressure guiding pipe will corrode and form a blockage.

Seven, the transmitter device itself failure problem

In the measurement of the lubricating oil pressure, the lubricating oil pressure signal participates in the stop interlock control. The signal obtained by the lubricant pressure transmitter is transmitted to the computer for display on the one hand. On the other hand, the signal is also compared by the program. When the pressure is lower than 0.06 MPa, the oil shortage stop signal is issued to stop.

From the trend diagram of the lubricant pressure signal, it is seen that the pressure is instantaneously falling and causing the machine to trip. After checking the transmitter, the internal module of the transmitter is found to be damaged. Although the transmitter is periodically calibrated every year, it is used for production after passing the test. After the transmitter has been running for several years, its performance indicators such as accuracy, sensitivity and stability will gradually decrease, and the internal diaphragm and integrated block will also be damaged.

Eight, there is interference problem

In the measurement of the air compressor exhaust pressure, the fluctuation of the exhaust pressure signal is large. After verifying the transmitter, it meets the accuracy requirements and eliminates the fault of the transmitter itself; check that the pressure guiding tube and the joint are not damaged or leaking, and the connection of the signal cable is in good contact. However, the direction of the cable is introduced into the control room through the cable tray next to the high compartment. There is a lot of electromagnetic interference around.