In the automatic production process, various instrument transmitters are indispensable instrumentation devices in the production equipment. It can detect several parameters such as level, flow, pressure, etc., providing operators with accurate and reliable information in time to ensure production capacity. Safe and smooth progress. But in the long run level transmitter during occasional power-down phenomenon, although very few opportunities arise, but also bring to normal production is relatively cumbersome instrument maintenance worker find its reason is very tricky, so It is of great significance to accurately and timely determine the cause of the fault. The following are the inspection methods for the four major faults of the differential pressure level transmitter.
1. The non-matching of the safety barrier causes no output and inaccurate measurement of the instrument. Because the intelligent liquid level transmitter requires the use of a safety barrier associated with it, when a safety barrier that does not have a matching license with the intelligent transmitter is used, it is Some of these problems will occur. The main reasons are: the voltage drop of the safety barrier is too high, the voltage of the entire circuit is lower than 16.4V, the power supply of the transmitter is insufficient, the loop cannot work, and the external resistance should be between 250Ω and 600Ω. Sometimes measuring the loop resistance > 700Ω, therefore causing measurement deviation, even the transmitter can not work; safety barrier is not intrinsically safe, causing a large common-mode interference signal, causing the smart transmitter does not work properly, making the transmitter no output. Therefore, the selection of a suitable safety barrier is also a necessary condition for ensuring that the transmitter can work normally. Although the instruments are compatible with each other, an intrinsically safe safety barrier is selected when the transformer isolated safety barrier should be used. Makes the instrument supply voltage insufficient, no independent power supply and the formation of anti-interference ability is poor, resulting in the transmitter can not work properly.
2. The liquid level transmitter has a circuit breaker A or B circuit breaker, which is also a factor that causes the transmitter to be without electricity. It is not easy to be detected. When the multimeter is used to measure the safety barrier 13 and 23 terminals, it shows that it has 24V. , but the transmitter did not receive power because of the open circuit from terminals 13 and 23 to the field transmitter.
3. The liquid level transmitter has a short circuit between the transmission line A and the line B, which is another important reason that causes the transmitter to lose power. The size of the short-circuit current depends on the power supply voltage and the loop resistance R. The current limiting resistor is selected appropriately. The short-circuit current Ik is limited to a rated value of 93mA or less. At this time, the safety barrier Ik=59mA. At this time, the voltages at 13 and 23 cannot be measured with a multimeter. The illusion for the examiner is that the safety barrier has no output voltage and is a safety barrier fault. In fact, there is no voltage drop in the short circuit of A and B lines. Simply check the circuit or measure the loop current to determine whether there is a short circuit.
4. An open circuit between the safety barrier 21 and the common terminal can also cause the transmitter to lose power. This failure is very difficult to find, because the safety gate power system is normal, the line A and B are neither continuous nor short circuit, often give the impression that the safety barrier itself can only fail, it is not true, because when the security gate 21 end or After the line from the public terminal to the DCS's FTA (File Termination Assembly field terminal assembly) is disconnected, the entire system does not constitute a loop, and the 23 terminal is vacant. The transmitter only receives the 24V+ from the 13 terminal, and the negative terminal has no power supply. The transmitter cannot Normal work.
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