Calibration
Comparing calibration of a normal (long, no flange) temperature sensor using a reference probe on the first picture, with a short sanitary sensor with a flange on the second one. We can see that the short sensor flange covers all the holes in the insert, so it is not possible to insert a normal reference temperature probe
reference sensor in the dry-block just does not work, because the internal reference sensor is located close to the bottom of the temperature block, and the short sensor to be calibrated is located in the very top part of the insert. The dry- blocks typically control the temperature gradient on a limited range in the bottom of the insert. The top part of the insert typically has a larger temperature gradient, so the top of the insert does not have the same temperature as the bottom of the insert. The size of the gradient depends on the temperature difference between the insert and environment, and how deep you go in the insert.
immersed into the same depth as the sanitary sensor to be calibrated. Optimally, the middle of the sensor elements should be aligned to the same depth. Also, the reference sensor needs to have a thin
flexible cable so that the cable can fit under the flange of the sanitary sensor. To help that, we can make a grove in the top of the insert where the reference sensor cable fits and the flange of the sanitary sensor still touches the top of the insert.
Short sensor without a clamp connection There are also short temperature sensors without the clamp connection and without the flange. With these sensors you should use an external reference sensor that has been immersed to the same depth as the sensor to be calibrated. The reference sensor should be as similar as possible with the sensor to be calibrated (similar diameter, similar response time, etc.). The internal sensor in the dry-block
cannot be used here either since it is located in the bottom of the temperature block and does not measure the same temperature as the short sensor.
DocUmentation, metrological traceability, calibration Uncertainty There are many additional things that are important in every calibration; as there are separate articles of many of these in this blog, I only briefly mention these here: As documentation is included in the formal
definition of calibration, it is a vital part of every calibration. This is naturally also valid in sanitary temperature sensor calibration. Typically, in the form of a calibration certificate. The calibration equipment used should have
a valid metrological traceability to the relevant standards, otherwise the calibration does not ensure traceability in the sensor calibration. The calibration uncertainty is a vital part in
The internal reference sensor is located in the bottom of the temperature block, while the short sanitary sensor is located in the very top part of the insert. There is a temperature gradient in the insert, causing the top of the insert being different temperature than the bottom. This is causing error in calibration
Using a dedicated short reference sensor As the internal reference sensor in the bottom of the dry-block is not suitable, we need to use a dedicated external reference temperature sensor. This reference sensor cannot anyhow be a
normal long reference sensor, as discussed earlier. The solution is to use a dedicated reference sensor that is short enough so that it can be
every calibration. If the calibration equipment (and calibration method and process used) is not accurate enough for the sensor calibration, then the calibration does not make much sense. I mean, what is the point of using a two per cent accurate calibrator to calibrate a one per cent accurate instrument.
Some example pictures of how the dedicated insert for sanitary sensor calibration could look like. The hole for the sanitary sensor and for the reference sensor are equally deep and there is a groove where the ref sensor cable can go
Naturally the structure of the temperature dry-
block needs to be such that the sanitary sensor with the flange fits to its place and touches the insert top end (in some dry-blocks the surroundings are preventing the flange to go deep enough to touch the top of the insert).
beamex SolUtion for Short Sanitary SenSor calibration The Beamex MC6-T is an extremely versatile portable automated temperature calibration system. It combines a temperature dry-block with Beamex MC6 multifunction process calibrator and communicator technology. The Beamex MC6-T150 temperature calibrator
model is perfectly suited for the application of calibrating this kind of short sanitary temperature sensor. The MC6-T150 can be provided with custom inserts to match your specific sensors. The Beamex SIRT-155 temperature sensor
is a very short and accurate temperature sensor with a thin flexible cable, designed to be a perfect companion with the MC6-T150 for this application. Using the MC6-T in conjunction with Beamex
A dedicated short reference sensor is located at the same depth as the short sanitary sensor to be calibrated, ensuring they are measuring the exact same temperature. Also, the reference sensor cable is in the grove, so it does not prevent the flange of the sanitary sensor to touch the top of the insert
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calibration software, CMX or LOGiCAL, enables you to digitise and streamline your whole calibration process. To learn more about calibration, please visit
Calibrating a short sensor (without a flange) using a short reference sensor
blog.beamex.com. Beamex
www.beamex.com January 2021 Instrumentation Monthly
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