Transmitter troubleshooting and treatment

Abstract: During the operation of power plants, transmitters are widely used, but sometimes various faults may occur. If the faults cannot be eliminated in time, it will seriously affect the safe and economical operation of the unit. Let’s talk about the failure and maintenance of pressure transmitters based on our own practical experience.

Transmitters are generally divided into pressure transmitters and differential pressure transmitters. Transmitters are commonly used to measure pressure, differential pressure, vacuum, liquid level, flow and density, etc. Transmitters can be divided into two-wire and four-wire systems, with two-wire transmitters being the most common. They can be divided into intelligent and non-intelligent, with more and more intelligent transmitters being used. They can be divided into pneumatic and electric, with electric transmitters being the majority. ; In addition, according to the application, there are intrinsically safe type and explosion-proof type; according to the application conditions, the main types of transmitters are as follows: low (micro) pressure/low differential pressure transmitter; medium pressure/medium differential pressure transmitter transmitter; high pressure/high differential pressure transmitter; absolute pressure/vacuum/negative pressure differential pressure transmitter; high temperature/pressure, differential pressure transmitter; corrosion-resistant/pressure, differential pressure transmitter; easy to crystallize/pressure, Differential pressure transmitter. During the operation of power plants, transmitters are widely used, but sometimes various faults may occur. If the faults cannot be eliminated in time, the safe and economical operation of the unit will be seriously affected. Let’s talk about the failure and maintenance of pressure transmitters based on our own practical experience. The sensitive components in the measurement part of the capacitive pressure transmitter adopt a fully welded structure. The electronic circuit part adopts wave soldering and connector installation methods. The overall structure is strong, durable and has few faults. For the vast majority of users, if a sensitive component is found to be faulty and cannot be repaired by themselves, they should contact the manufacturer to replace the entire component.

1 Inspection of the measuring part of the transmitter

Faults in the measuring part of the transmitter will cause the transmitter to have no output or abnormal output, so the transmitter should be checked first. Measure sensitive parts. a. Remove the flange and check whether the isolation diaphragm of the sensitive component is deformed, damaged or leaking oil. b. Remove the compensation board without taking out the sensitive components and check the insulation resistance of the pin housing. The insulation resistance should not be less than 100MΩ when the voltage does not exceed 100V. c. Connect the circuit and gas path. When the pressure signal is at the upper limit of the range, close the gas source. The output voltage and reading value should be stable. If the output voltage drops, it means there is a leak in the transmitter. Use soapy water to check the leakage location.

2 Inspection of the circuit part of the transmitter

2.1 After turning on the power and giving the input pressure signal, check the voltage at the output end of the transmitter

The signal state. If there is no output voltage, you should first check whether the power supply voltage is normal and meets the power supply requirements. There are no wiring errors between the power supply, the transmitter and the load equipment. If there is no voltage on the transmitter terminals or the polarity is reversed, the transmitter will output no voltage signal. If the above reasons are eliminated, you should further check whether the components in the circuit of the amplifier board are damaged and whether there is any bad contact in the connectors of the circuit board. You can determine the necessary circumstances of the fault point by comparing the measured voltage of the normal instrument with the corresponding measured voltage of the faulty instrument. Faulty amplifiers can be replacedplate. When inspecting the flow transmitter, special attention should be paid to anti-static measures for the J-type amplifier board.

2.2 After the power is turned on and the input pressure signal is given, if the output of the transmitter is too high and greater than 10VDC or the output is too low and less than 2.0VDC, and the output does not respond when the input pressure signal is changed and the zero point and range screws are adjusted. . For this type of fault, in addition to checking whether there are any abnormalities in the sensitive components of the measurement part of the transmitter, you should also check whether the "oscillation control circuit part" on the transmitter amplifier board is working properly. The normal peak voltage between high frequency transformer T1-12 should be 25~35VP-P and the frequency is about 32kHz. Secondly, check the working condition of each operational amplifier on the amplifier board and whether the components of each part are damaged. This type of failure requires replacement of the amplifier board.

2.3 The transmitter has very strict requirements on circuit design and process assembly quality. In actual use, the graphic and text dynamic synchronization competition will be conducted after the circuit faults that occur are inspected and confirmed.