What should the insulation resistance of the instrument signal wires to ground be to not affect measurements?
Thread Content
During work today, an abnormality was detected with one instrument; the insulation resistance between the signal wires and the conduit was 22 megohms. There was disagreement among those present regarding this issue. I would like to ask the experts here: what should the insulation resistance be between the instrument’s signal wires and the conduit so as not to affect measurements?
The current signal should generally be infinite; I haven’t tried to find out what the minimum value could be. The insulation resistance of thermocouple signals can be quite low – some devices can still function with values in the range of a few megohms. As long as it works properly when tested with a signal generator, that’s fine!
The insulation resistance of the instrument signal wires relative to ground should be 4 ohms without any impact on the measurements
4 ohms? That’s impossible! ! !
For the one on the 3rd floor, the 4 ohms you’re referring to is likely the resistance of the instrument signal ground, not the instrument signal wire.
Theoretically, it seems that a value greater than 20 megohms is sufficient, but in practice, the values you have measured indicate that the grounding of your signal lines is poor.
Theoretically, it should be infinite; if it’s 20 megohms, then it should work.
An insulation resistance of 22 megohms should not present any problems. Abnormal readings from instruments are generally not related to insulation resistance; they are usually caused by interference or poor shielding. It is possible to check whether the shielding grounding is secure and whether the grounding resistance meets the required standards – generally, the grounding resistance should be less than 4 ohms~~
Under normal circumstances, does insulation resistance also affect the detection? Incredible.
22M ohms should be fine; I also tested it on-site, and most values were in the range of seventy to eighty megohms