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How to judge the fault of the capacitive level gauge?
- 2019-05-31-

The capacitive liquid level meter is composed of a sensor, a transmitter, a light column display regulator, a 24V power supply and a power supply cable. As long as one of the parts fails, it will affect the normal use of the capacitive level gauge. In order to judge whether each part is working properly and to treat the disease, you can check it according to the following steps.

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

2. Check the power supply of the transmitter: After power-on, check whether the independent power supply has 24V output with a multimeter; 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 transmitter: disconnect the connection line between the transmitter and the sensor, then connect one end of the sensor to A, and connect one end of the transmitter to B. At this time, connect the transmitter. After the power supply, the indication should be zero, short circuit B to ground, the output current of the transmitter can be increased to more than 20mA, the short circuit of B to ground is disconnected, and the transmitter returns to zero position, indicating that the transmitter is normal; Otherwise, the transmitter should be replaced.

5. Check the sensor: After disconnecting the A and B lines, 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 a multimeter The capacitance file measures the capacitance value of the A terminal to the ground, generally between tens and hundreds of PF, and should change with the change of the liquid level, indicating that the sensor is normal. Otherwise, the sensor should be replaced.

We judge and analyze with common fault phenomena:

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 value will be zero, the problem is on the sensor. At this time, check the insulation resistance of the sensor A and ground with a 1000V megger. If the resistance is below 150 megohms (measured at normal operating pressure), the sensor should be replaced.

(2) After disconnecting the A and B wires on the transmitter, if the output current value is still above 20mA, it means that the fault is on the transmitter, the light column display regulator, the 24V power supply and the power supply cable, respectively. The part is further checked to determine the fault location.

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

(1) Disconnect the A and B connecting wires on the transmitter, and make the B terminal short-circuit to the ground. If the output current value of the transmitter rises to the maximum, the sensor is open; use the capacitance of the multimeter to measure the capacitance of the sensor. Between tens to hundreds of PFs, and can vary with liquid level; otherwise, the sensor should be replaced.

(2) Short-circuit the B terminal 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 to determine the fault location.

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