Problem with Pt100 readings on V700

[Oldskuler]

Hi to all!

I have the configuration of V700 + IO-PT4x cards.

We have 12 pt100 sensors, all of them are extended with 5-6m cables (I have exactly the same configuration in the same factory and everything runs great).

Readings that I'm getting are very unstable, for example, in 3s, it changes from 10 to 20°C and goes down, and so on. When I replace those sensors with sensors that are not extended, readings are stable.

Then I thought that some kind of interference are in the cable extensions, but I measured the resistance of each extended sensor and the readings are stable (ohms).

I'm still thinking that the interference is happening, but as I mentioned earlier, exactly the same configuration is running in the past 3 years and there are no problems.

Does anyone have some tips on what can I check to try to resolve this?

Thank you in advance.

[DanT]

Hi;

How are the sensors wired?    2 wire 3 wire or  4 wire set up?

Any loose connections?

Is the cabling shiended?

Is the tip of the PT400 actually isolated from ground?

Is the cabling kept away from high voltage and any VFD wiring( if present)?

DanT

 

[Oldskuler]

59 minutes ago, DanT said:

Hi;

How are the sensors wired?    2 wire 3 wire or  4 wire set up?

Any loose connections?

Is the cabling shiended?

Is the tip of the PT400 actually isolated from ground?

Is the cabling kept away from high voltage and any VFD wiring( if present)?

DanT

 

Hi,

thank you for your reply.

1. It is 2 wire connection.

2 No loose connections.

3. In the meantime I found out that the colleague who did the wiring used a shielded cable, but he didn't connect the shield to the ground (didn't use it at all).

4. Thank you for this, I didn't check it, but I will do it.

5. Yes, cables are away from any voltages and VFDs.

[Fernando Castro]

23 hours ago, Oldskuler said:

Hi,

thank you for your reply.

1. It is 2 wire connection.

2 No loose connections.

3. In the meantime I found out that the colleague who did the wiring used a shielded cable, but he didn't connect the shield to the ground (didn't use it at all).

4. Thank you for this, I didn't check it, but I will do it.

5. Yes, cables are away from any voltages and VFDs.

Also, double check your grounding on the PLC.