RTD sensors calibration equipment

In summary, a user named Tom asked for advice on calibrating RTD sensors in a chemistry lab, where they were confined to their electronics work room. Another user suggested using fix points and interpolating for calibration, but Tom also considered using a water bath for calibration. A third user suggested expensive instruments for calibration, but Tom also mentioned using an ice bath and obtaining good results. The user advised allowing for equilibration time when using a dry block or similar controlled source.
  • #1
Tomcat
5
0
Hello !

This is my first post on the Physics Forums. I am electronics technician employed in mass spectrometry laboratory at RBI Institute, Zagreb, Croatia.

My question is related to calibration of RTD sensors, which I must do in another lab or division, and since I developed prototype of RTD based neasuring device (based on 0.1%, class B RTD Pt100 sensor) there is possiblity that I need to make more of these. Is there possibility of construction of RTD calibrating equipment ? Is there reliable design of calibration device or cell which can be done, keeping in mind that I am working in chemistry lab but I am, regarding of expenses and equipment for this project, confined into my electronics work room.

Thank you !

Tom
 
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  • #2
For which temperature range?

I recently discussed something similar with people who work in this area. PT100 sensors are -from what I understand- extremely linear and reproducible so you can get away with using a couple of fix points and the interpolate. If you are working at room temperature this means and ice-bath for 0 degrees C and then boiling water for 100 degrees C. The only intermediate point is the melting point of gallium, which is probably not practical in a normal lab setting.

That said, from a practical point of view you can just as well just get ONE properly calibrated sensor and then -using a water bath- use it to calibrate the rest of you sensors.
 
  • #3
f95toli said:
For which temperature range?

I recently discussed something similar with people who work in this area. PT100 sensors are -from what I understand- extremely linear and reproducible so you can get away with using a couple of fix points and the interpolate. If you are working at room temperature this means and ice-bath for 0 degrees C and then boiling water for 100 degrees C. The only intermediate point is the melting point of gallium, which is probably not practical in a normal lab setting.

That said, from a practical point of view you can just as well just get ONE properly calibrated sensor and then -using a water bath- use it to calibrate the rest of you sensors.


Thank you for you answer. Well, this is actually what I discussed with my colleagues and I am glad you have the same opinion - we will calibrate ONE sensor on our Institute of Physics (they have equipment and standards). We could calibrate according to their standard RTDs and by doing this make our own reference sensor.

Now, since we won't go outside of 100 degrees C (and this is the limit below which is Pt100 considered perfectly linear), we currently use only this formula in our microcontroller to "fit" data to the RTD characteristics curve:

http://www.mosaic-industries.com/em...inum-rtd-sensors/resistance-calibration-table

T = (R/R0 – 1)/α - 0.19

Of course, this works in case that all RTD's fit to this curve. So, if I obtain class A RTD (Pt100), and this implies accuracy of 0.04 degrees C, fit data from ADC according to above expression, I should get excellent accuracy. IF you don't agree, please correct me. :)

But, I will follow your advice and use ice bath to check RTD and after that put it to the calibration in equipped lab.

Obviously, calibration equipment making is too much.

Thanks !

Tom
 
  • #4
When performing temperature calibrations while working for a pharmaceutical company where accuracy and traceability to NIST was a FDA requirement, I used this http://www.kayeinstruments.com/validationproducts/irtd.htm as a standard. It is quite expensive however.

http://www.kayeinstruments.com/img/cd_calibration_irtd2.jpg [Broken]

For a temperature reference, I used one of these http://www.kayeinstruments.com/validationproducts/drywell.htm.

http://www.kayeinstruments.com/img/cd_calibration_irtd_2.jpg [Broken]
 
Last edited by a moderator:
  • #5
dlgoff said:
When performing temperature calibrations while working for a pharmaceutical company where accuracy and traceability to NIST was a FDA requirement, I used this http://www.kayeinstruments.com/validationproducts/irtd.htm as a standard. It is quite expensive however.

http://www.kayeinstruments.com/img/cd_calibration_irtd2.jpg [Broken]

For a temperature reference, I used one of these http://www.kayeinstruments.com/validationproducts/drywell.htm.

http://www.kayeinstruments.com/img/cd_calibration_irtd_2.jpg [Broken]

Thank you very much for this info. These are obviously excellent instrumets. This standard RTD probe from GE would be the most suitable for our purpose. Even if it is expensive, now I've got good reference for further search.

Tom
 
Last edited by a moderator:
  • #6
f95toli said:
For which temperature range?

I recently discussed something similar with people who work in this area. PT100 sensors are -from what I understand- extremely linear and reproducible so you can get away with using a couple of fix points and the interpolate. If you are working at room temperature this means and ice-bath for 0 degrees C and then boiling water for 100 degrees C. The only intermediate point is the melting point of gallium, which is probably not practical in a normal lab setting.

That said, from a practical point of view you can just as well just get ONE properly calibrated sensor and then -using a water bath- use it to calibrate the rest of you sensors.

Hello.

I just did ice bath measurement, using small dewar flask, but due to the nature of the sensor, e.g. it's proximity to the PCB, I was not able to do constant stirring of the ice/water mixture. Although results show some instability, there was period of very nice distributed values from 0.12 to 0.15 degrees C and that was most certainly period of ideal mixture behaviour (other results were very erratic and these good values are measured immeditely after mixture stirring). So, I guess, sensor is checked, now we need to do some fine tuning in better equipped lab.

Thank you for your help.



Tom
 
  • #7
Tomcat said:
Although results show some instability, there was period of very nice distributed values from 0.12 to 0.15 degrees C ...
You need to allow plenty of time for the temperature source equilibration after you reach the desired value (using a dry block or similar controlled source). I would allow at least 30 minutes to guarantee stability at each calibration point. Here again, I talking about using the source and standard that I referenced.
 
  • #8
dlgoff said:
You need to allow plenty of time for the temperature source equilibration after you reach the desired value (using a dry block or similar controlled source). I would allow at least 30 minutes to guarantee stability at each calibration point. Here again, I talking about using the source and standard that I referenced.

You are right, I'll repeat the procedure. Of course, I'll need to make some adjustment (fix RTD and electronics on laboratory stand as well as make system to slowly stir the ice bath mixture while measuring). Problem is that RTD is intended to be very close to electronics circuit board (cca 10mm), RTD itself is very small, so immersion shuold be done very carefully. So, that is the next step - making fixed setup, let it stabilize and log data all the time.

Tom
 

1. What is an RTD sensor calibration equipment?

An RTD (Resistance Temperature Detector) sensor calibration equipment is a device used to calibrate and verify the accuracy of RTD sensors. RTD sensors are electronic devices used to measure temperature by detecting changes in resistance as temperature changes. The calibration equipment ensures that the readings from the sensor are accurate and within the required range.

2. How does RTD sensor calibration equipment work?

The calibration equipment works by applying a known temperature to the RTD sensor and comparing the sensor's output to the expected value. If there is a difference in the readings, the equipment can make adjustments to the sensor's output to ensure accuracy. The process is repeated at different temperatures to verify the sensor's accuracy across its operating range.

3. Why is RTD sensor calibration important?

RTD sensors are used in many industrial and scientific applications where temperature measurement is critical. Inaccurate readings from these sensors can lead to faulty processes, equipment damage, and safety hazards. Regular calibration using specialized equipment ensures that the RTD sensors provide accurate and reliable temperature measurements.

4. How often should RTD sensors be calibrated?

The frequency of calibration depends on the specific application and the manufacturer's recommendations. In general, RTD sensors should be calibrated at least once a year, but more frequent calibrations may be necessary for critical applications or in harsh environments. Regular calibration also helps to detect any drift in the sensor's accuracy and allows for timely adjustments.

5. Can RTD sensor calibration equipment be used for other types of temperature sensors?

RTD sensor calibration equipment is specifically designed for calibrating and verifying the accuracy of RTD sensors. However, some equipment may also have the capability to calibrate other types of temperature sensors, such as thermocouples or thermistors. It is important to check the equipment's specifications and capabilities before attempting to calibrate a different type of sensor.

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