I. Inspection of the measuring part of the transmitter The fault generated by the measuring part of the transmitter will cause the transmitter to have no output or abnormal output. Therefore, the sensitive parts of the transmitter should be checked first.
1. Remove the flange and check the isolation diaphragm of the sensitive parts for deformation, damage and oil leakage.
2. Remove the compensating plate, do not take out the sensitive parts, check the insulation resistance of the plug for the housing. When the voltage does not exceed 100V, the insulation resistance should not be less than 100MΩ.
3. Turn on the circuit and the 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 has a leak and the leak can be detected with soapy water.
Second, the inspection of the transmitter circuit part Turn on the power and check the status of the voltage signal at the output of the transmitter after the input pressure signal is given. If there is no output voltage, first check whether the power supply voltage is normal; whether it meets the power supply requirements; there is no wiring error between the power supply and the transmitter and load equipment. If there is no voltage on the transmitter terminal or the polarity is reversed, the transmitter can output no voltage signal. If the above reasons are excluded, the component of the amplifier board line should be further inspected for damage; if the circuit board connector has poor contact, the method can be used to determine the fault by comparing the measured voltage of the normal meter with the measured voltage corresponding to the faulty meter. Point, replace the faulty amplifier board if necessary. When checking the flow type transmitter, special attention should be paid to the J type amplifier board to take anti-static measures.
2. Turn on the power. After the input pressure signal is given, if the transmitter output is too high (greater than 10VDC), or the output is too low (less than 2.0VDC), and the input pressure signal is changed and the zero point and span screw are adjusted, the output will not respond. . For such faults, in addition to checking the sensor for sensitive parts of the measurement part, check whether the "oscillating control circuit part" on the transmitter amplifier board works normally or not. The normal peak voltage between the high-frequency transformer T1-12 should be 25~35VP-P; the frequency is about 32kHz. Next, check the operation status of each operational amplifier on the amplifier board; whether the components of each part have damage or not. This type of fault requires the replacement of the amplifier board.
3. Transmitter requirements are very strict in line design and process assembly quality. In actual use, after the line fault occurs, it is best to contact the manufacturer to replace the faulty circuit board after checking and confirming to ensure the stability of the instrument for long-term work. And reliability.
III. On-site fault inspection Most of the faults at the construction site are caused by improper use and installation methods. There are several aspects summarized.
1. The primary component (orifice plate, remote measurement connector, etc.) is blocked or installed in the wrong form, and the pressure point is unreasonable.
2. Leakage or blockage of the pressure guiding tube, residual gas in the liquid filling tube or residual liquid in the inflation tube, deposits in the process flange of the transmitter, forming a dead zone.
3. The transmitter wiring is incorrect, the power supply voltage is too high or too low, indicating that the contact between the meter head and the meter terminal is poor.
4. It is not installed in strict accordance with the technical requirements, and the installation method and on-site environment do not meet the technical requirements.
The above faults will cause the transmitter output to be abnormal or the measurement is not accurate, but after careful inspection, strictly use and install according to the technical requirements, take effective measures in time, the problem can be eliminated, and the fault that cannot be handled should be transmitted. The device is sent to the laboratory or the manufacturer for further inspection.
Capacitive pressure transmitters measure all sensitive parts with all-welded structure, and the electronic circuit part adopts wave soldering and connector mounting. The overall structure is firm and durable, and there are few faults. For the vast majority of users, if it is found that the sensitive parts are faulty, it is generally impossible to repair them by themselves. Contact the manufacturer to replace the whole parts.