Siemens SITRANS MAG 1100 Operating Instructions Manual page 48

Troubleshooting
7.2 Sensor check
Coil resistance check
● Measure the coil resistance between connection numbers 85 and 86 using a digital meter.
A low reading may indicate moisture within the coil housing or shorted coil tums.
A high reading would indicate an open circuit coil.
Note
In case of deviation from nominal coil values, the sensor is damaged and must be replaced
Coil insulation check
Potential hazard!
Only carry our a coil insulation check in non-hazardous area!
● Megger between connection number 85 and the sensor body.
A low megger reading would indicate the coil insulation is breaking down. This is normally due
to fluid ingress into the coil housing.
Sensors with an insulation resistance down to 1 MΩ may still work satisfactorily but this is not
guaranteed.
Electrode resistance check
● Measure the electrode resistance between connections 82 and 0 with a moving coil meter.
● Repeat the resistance measurements between connections 83 and 0.
If the resistance is low there may be a short on the electrodes or wiring (in the case of a remote
mounted transmitter). Alternatively there may be water ingress or moisture in the terminal box.
If the resistance is high and the pipe is completely full of fluid check the following:
1. Fluid is electrically conductive.
2. Electrodes are not coated with grease or any deposit.
3. Electrode circuit is not open.
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Resistance should be within range stated in Coil resistance table (Page 68).
WARNING
The resistance should be above 20 MΩ.
With a sensor full of fluid the resistance should be between 5 KΩ and 50 KΩ.
If the sensor is empty the resistance will be infinite.
The results should be the same.
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