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PT100 unstability

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PT100 unstability

Postby guest » Wed Oct 11, 2006 10:31 am

Hi,
I am currently experiencing stability problems when setting up two PT-104 converters.
I have one converter connected to my PC via a USB converter lead which has four 4-wire PT100 sensors connected to it. The second converter is connected to the PC via the serial port and has two 4-wire PT100 sensors connected to it.
These units are immersed in three oil baths (2 probes per bath) at a temperature of 160°C.
I am experiencing wildly fluctuating temperatures on the channel 3 probe connected to the USB PT104, and also on both probes on the Serial PT-104. However when i remove any of these PT100's from the oil bath and manually hold the PT100 in the bath (ie not touching any part of the bath itself) the readings stabilise at 160°C.

The PT100's were supplied with the PT-104 converters from Picotech.

I suspect this may be a PT100 wiring or grounding problem as i can swap the faulty PT100 probes into other ports and the fault occurs no matter which port the probe is connected to

Thanks for you assistance
guest
 

Postby Michael » Wed Oct 11, 2006 11:01 am

Hello Guest,

I think you are right here. This appears to be a grounding issue with the laptop and power supply. Try running the laptop on batteries to see if the temps stabilise.

To correct the problem, try connecting an earth bond from the serial port outer shell of the PT104 to the oil bath or earth.

Please let me know how you get on.

Best regards,
Michael
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Postby Guest » Wed Oct 11, 2006 11:52 am

Hi Michael thanks for the prompt reply.

I'm not actually running a laptop to run the software but a dedicated desktop, I understand the grounding issues but what puzzles me is why 3 of the probes on the first converter are reading correctly but the fourth is unstable, as I have swapped the probes around and the problem does not appear to be the converter but the PT100 probes.

As these probes were bought directly from Picotech, can you tell me if they are grounded to the sheath or ungrounded and do i need to connect the PT100 cable shield to the casing of the minidin connector. (I have never had to do this with PT100's)

We also run a similar logging system on identical baths (SPECVIEW) and have had no grounding issues with this installation

Thanks
Guest
 

Postby Michael » Mon Oct 16, 2006 10:17 am

Hello,

Are you prepared to return the suspect probe to us for investigation?

Is so, please email me on support@picotech.com

Best regards,
Micheal
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