1

I need to monitor temperature between -15°C and +40°C. The transducer(Pt100 probe and R/I transmitter) can measure between -25°C to 72°C. But I need the temperature transducer to be calibrated by an institute. The thing is that they calibrate between +15°C and +30°C.

Is that fine or a custom to calibrate a narrower interval than the range used? I have no experience with that and was a bit confused. Does anyone have experience with that? Should the measurement be inside the calibration range?

cm64
  • 2,139
  • 1
  • 19
  • 46

1 Answers1

0

In general it would not be acceptable to measure outside of the calibration range, that would mean you'll be extrapolating and you can not guarantee the uncertainty of your measurement anymore.

But it all depends on the accuracy you need to get.

Based on how your question is phrased I imagine you have a project requirement to have your instruments calibrated by a third party with certificates and all that. If that's the case, you can ask them to give you the uncertainty you would get with their standard and your custom range together with the cost and then decide if you want to pay for the improved calibration. You might even be surprised to find that the calibration from the manufacturer (so no third party calibration) is better than the lab's standard range.

Marcos G.
  • 443
  • 5
  • 7
  • Here is the trasnducer https://www.prelectronics.com/pdf/3102-8621-US.pdf and the probe https://www.prelectronics.com/pdf/7430B-2988-US.pdf The transducer datasheet says: "Accuracy.Better than 0.1% of sel. range" Does that mean in any case in measurement range this accuracy is valid? Normally one sets sets the temper. range by DIP switches and % of 0-10V voltage relates to temperature. But if I get this calibrated between 15 to 40C can I use the same transfer function for -15C? – cm64 May 21 '19 at 12:36
  • Quite nice equipment you have there. According to the datasheet, you should be able to get temperature to within 0.2 C. From the 1000 available factory calibration settings you have available you should be able to stay not that far away from that out of the box. I think it would be more like 0.3 C (see here for instance: https://de-de.wika.de/upload/DS_IN0017_en_co_20804.pdf ). If you need to improve on that I don't think you'll be able to do it calibrating from 15 to 30 C and extrapolating. – Marcos G. May 21 '19 at 15:20
  • And I think that the worst part is that, if you send your sensor for calibration to a lab they will indeed give you a new set of calibration coefficients that most likely won't be available in your signal converter, so you'll have to add a new step in your software (PLC or computer) if you are to get the improve accuracy. – Marcos G. May 21 '19 at 15:25
  • By the way, if you do want to improve on these "standard industry" accuracies it should not be that difficult at least down to -20 C. See for instance: https://www.sterlingsensors.co.uk/calibration . But it won't be an off-the-shelf setup like the one you have now – Marcos G. May 21 '19 at 15:55
  • A couple of resources that might help you: http://www.burnsengineering.com/local/uploads/content/files/Calibration-Why_When_How_Handout.pdf . If you are cash rich you might even consider one of these: http://download.flukecal.com/pub/literature/6005929_0000_ENG_A_W.pdf – Marcos G. May 21 '19 at 16:36