Low Temperature Deviation Issue with Hart Scientific 5615 RTD

I have no actual experience with these devices.

I can make some suggestions as to how you might proceed.

It's not quite clear to me what your set up looks like - does each sensor have its own read out device or are you using 1 read out device with 5 different sensors.

If the 5615 sensor is always used with the same read out device ( by which I mean the same single physical device, not just the same make and model)  then you can not tell if the errors comes from the read out device or the sensor.

How does the calibration work - is it electronic or paper - what does the calibration of the 5615 look like compared with the other sensors.

What does the error profile look like "Below 0 °C, the 5615 starts to deviate by approximately 0.2°C" isn't specific enough - a graph would help.

Is 20 minutes long enough (a graph of reading against time would tell).

What are the differences between the sensors (dimensions, cable, connectors etc.)

What do Fluke have to say about it ?

MK

Thank you so much for your reply.

Each sensor in my setup is paired with its own dedicated readout device, and they are calibrated together as a system. Because of this, I can’t swap instruments. The sensor that shows the deviation is a different model from the others, although all of them are Hart Scientific RTDs and those particular sensors were calibrated by the same lab on the same range of temperature -50 to 150 °C.

The deviation of about 0.2 °C below 0 °C is clearly beyond what would be expected for this class of sensor. To be more precize for instance when I go to -20 °C the 4 other sensors show values around -19.923°C and the 5615 sensor shows a value around -19.710°C. This is very strange because it behaves like that only for those low temperatures and behaves correctly for the rest. I will try and simulate a stabilization curve to be sure (thanks for the idea), however 20 minutes should be more than enough for thermal equilibrium in this setup (according to specifications and my past measurements done with this sensors.)

All sensors use the same cables, connectors, and immersion depth P1, so there are no physical differences that could explain the issue. In the image above you can find my attempt to schematize my setup.  I haven’t contacted Fluke yet, but that’s the next step I plan to take.

Thanks again for your insights they’ve really helped me clarify my approach and think more.

Thank you so much for your reply.

Each sensor in my setup is paired with its own dedicated readout device, and they are calibrated together as a system. Because of this, I can’t swap instruments. The sensor that shows the deviation is a different model from the others, although all of them are Hart Scientific RTDs and those particular sensors were calibrated by the same lab on the same range of temperature -50 to 150 °C.

The deviation of about 0.2 °C below 0 °C is clearly beyond what would be expected for this class of sensor. To be more precize for instance when I go to -20 °C the 4 other sensors show values around -19.923°C and the 5615 sensor shows a value around -19.710°C. This is very strange because it behaves like that only for those low temperatures and behaves correctly for the rest. I will try and simulate a stabilization curve to be sure (thanks for the idea), however 20 minutes should be more than enough for thermal equilibrium in this setup (according to specifications and my past measurements done with this sensors.)

All sensors use the same cables, connectors, and immersion depth P1, so there are no physical differences that could explain the issue. In the image above you can find my attempt to schematize my setup.  I haven’t contacted Fluke yet, but that’s the next step I plan to take.

Thanks again for your insights they’ve really helped me clarify my approach and think more.