Capacitive pressure transmitter fault inspection method

Capacitive pressure transmitter is a commonly used measuring instrument. It can convert the physical pressure parameters such as gas and liquid that are sensed by the load cell sensor into a standard electrical signal output. Capacitive pressure transmitters will also have certain faults during use. The user needs to know how to troubleshoot the capacitive pressure transmitters. Here's a look at the specifics.

First, the transmitter measurement part of the inspection

Any malfunction caused by the measuring part of the transmitter will cause the transmitter to have no output or the output is abnormal. Therefore, the transmitter's measurement-sensitive parts should be checked first.

1. Remove the flange and inspect the isolation diaphragm of the sensitive part for deformation, damage, and oil leakage.

2. Remove the compensation plate, do not take out the sensitive parts, check the insulation resistance of the plug-in case, and the insulation resistance should not be less than 100MΩ when the voltage does not exceed 100V.

3. Turn on the circuit and gas circuit. When the pressure signal is the upper limit of the range, turn off the gas source, and the output voltage and reading value should be stable. If the output voltage drops, the transmitter is leaking and you can use soapy water to check for leaks.

Second, the transmitter circuit part of the inspection

1. Turn on the power and check the status of the voltage signal at the output of the transmitter. If there is no output voltage, first check whether the power supply voltage is normal; whether it meets the power supply requirements; whether there is any wiring error between the power supply and the transmitter and the load device. No voltage or reversed polarity on the transmitter terminals can cause the transmitter to output no voltage signal. Exclude the above reasons, you should further check the amplifier board circuit components for damage problems; circuit board connectors have no contact with the phenomenon of bad, you can use the measured voltage of the normal instrument and the fault meter corresponding to the measured voltage compared to the method to determine the fault Point, if necessary, replace the faulty amplifier board. When checking flow-type transmitters, special attention should be paid to J-type amplifier boards to prevent static electricity.

2. After power on, if the transmitter output is too high (more than 10VDC) or the output is too low (less than 2.0VDC) after the input pressure signal is given, the output will be changed if the input pressure signal is changed and the zero point and range screw are changed. No reaction. For this kind of fault, in addition to checking whether there are any abnormalities in the sensitive parts of the transmitter's measurement part, check whether the “oscillation control circuit part” on the transmitter's amplifier board is working properly or not. The normal peak voltage between high-frequency transformer T1-12 should be 25 ~ 35VP-P; frequency is about 32kHz. Secondly, check the operational status of each operational amplifier on the amplifier board; whether the components of each part are damaged or not. This type of fault requires the replacement of the amplifier board.

3. The transmitter is very strict in the line design and process assembly quality. In the actual use of the line fault, after the inspection and confirmation, it is best to contact the manufacturer to replace the faulty circuit board to ensure the long-term work of the instrument. Stability and reliability.

Third, on-site troubleshooting

The majority of failures at the construction site are due to improper use and installation methods, and they are summarized in several ways.

1. The primary component (orifice plate, remote measurement connector, etc.) is blocked or improperly installed, and the pressure point is unreasonable.

2. Leakage or blockage of the pressure tube, residual gas in the fluid filled tube or residual fluid in the aeration tube, deposits in the process flange of the transmitter, forming dead space for measurement.

3. The transmitter is wired incorrectly and the power supply voltage is too high or too low, indicating poor contact between the meter header and the meter terminal block connections.

4. The installation was not strictly in accordance with the technical requirements. The installation method and the site environment did not meet the technical requirements.

The above failures will cause the transmitter output is not normal or the measurement is inaccurate, but after careful inspection, strictly in accordance with the technical requirements of use and installation, take effective measures in a timely manner, the problem can be ruled out, the failure can not be handled, should be transferred The device is sent to a laboratory or manufacturer for further inspection.