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Capacitance level gauge fault and judgment
- 2019-06-14-

The capacitive liquid level gauge is composed of a sensing probe, a transmitter, a light column display regulator, a 24 V power supply and a power supply cable. As long as one of the parts fails, it will affect the normal use of the product. In order to judge whether each part is working properly and to treat the disease, it can be checked in the following manner.

1. Check the light column adjuster: After power on, you can check according to the instruction manual of the light column display regulator.

2. Check the power supply of the transmitter: Check whether the power supply has 24V output after power-on; if it is directly powered by the light column display regulator, check whether the 24V power supply is normal.

3. Disconnect the cable between the transmitter and the light column display regulator. Check the open circuit of the cable with the resistance file of the multimeter. Is the insulation resistance of each cable to ground good? The insulation resistance is normal. Unlimited.

4. Check the capacitive transmitter: disconnect the connection between the A and B terminals on the transmitter, A is the output of the sensing probe, and B is the input of the transmitter; After the transmitter is energized, it should return to the zero position. After the B is shorted to the ground, the output current of the transmitter can be increased to more than 20mA. The short circuit of B is disconnected from the ground, and the transmitter returns to the zero position, indicating the transmitter. It is normal; otherwise, the transmitter should be replaced.

5. Check the sensing probe: After disconnecting the connection between the A and B terminals, measure the insulation resistance of the A end to the ground with a 1000V megger. Normally, it should be greater than 150 megohms (measured under normal working pressure) ); use the capacitance of the multimeter to measure the capacitance value of the A terminal to the ground, generally in the range of tens to hundreds of picofarads, and should change with the change of the liquid level, indicating that the sensing probe is normal.

We help analyze the common fault phenomenon:

1. The output current of the transmitter exceeds 20mA regardless of the liquid level change.

(1) Disconnect the A and B wires on the transmitter. If the output current will be zero, the problem is on the sensing probe. At this time, check the insulation resistance of the probe A and ground with a 1000V megger. If the resistance is below 150 megohms, the sensor probe should be replaced.

(2) After disconnecting the A and B wires on the transmitter, if the output current value is still the maximum, it indicates that the fault is on the transmitter, the light column display regulator, the 24V power supply and the power supply cable, respectively, and their respective Partially check and judge the fault location.

2. The transmitter has no current output regardless of the liquid level change.

(1) Disconnect the A and B wires on the transmitter, short-circuit the B terminal to the ground, and increase the output current of the transmitter to the maximum, indicating that the sensing probe is open; measure the capacitance of the sensing probe with the capacitance of the multimeter. The values are generally between tens and hundreds of picofarads and can vary with the level of the liquid; otherwise, the sensing probe should be replaced.

(2) After the B end is shorted to the ground, if the transmitter still has no current output, the fault appears on the transmitter, the light column display regulator, the 24V power supply and the power supply cable, and can be separately checked and the fault location is judged.

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