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Decontamination Process Validation

Temperature Calibration Guidance

Choosing the Right Calibration Parameters


Setting Calibration Parameters

Typically the low and high point for calibration should be just below and just above the temperature range under test. Although the calibration curve is smooth and the whole curve is adjusted, so temperatures just outside the set points are almost certainly accurate, these may not be accepted by an auditor.

There is considerable discussion regarding the placement of the check point:

  • Mathematically the point with greatest deviation (i.e. greatest inaccuracy) is halfway between the correction points, so if this point can be shown to be within accuracy limits the entire range must therefore also be within the limits.
  • Traditionally many people use the critical temperature of the machine under test as the check point (e.g. 134 °C for an autoclave), which may be very close to one end of the calibration range. While this demonstrates the accuracy of measurements at this point you should be aware that the calibrated accuracy may decrease closer to the midpoint.
Calibration Setup(1)

The Stability Settings allows you to set the stability parameters applied during calibration. For example 0.2 degrees per minute for 2 minutes instructs TQSoft to watch all probes and begin a stability countdown once no probes have changed by more than 0.2 °C for one minute. If no probes deviate by more than 0.2°C for the duration of the 2 minute countdown, stability will be deemed to have been achieved, and the temperatures at that point used to create the required calibration offsets. A smaller deviation will create a more accurate calibration and a longer time period create a higher guarantee of stability, but both will increase the time taken to stabilise and the risk of one or more probes being unable reach stability.

Allowed deviation from Reference dictates how much the readings from each probe before calibration can deviate from the reading from the Reference Probe (in effect how far the calibration can ‘move’ the reading) before TQSoft marks the probe as faulty.

Reference Stability Criteria dictates the degree of fluctuation allowed in the Temperature Reference before TQsoft deems it to be stable. The tolerance for this is usually tighter than that for the temperature probes under calibration (for instance 0.1°C or even 0.05°C over 1 minute). This is partly because the capability of the reference (often a PT100 probe) is generally greater, and because calibrating against a temperature that is fluctuating will introduce uncertainties.

Note that TQSoft will being a countdown once it deems stability has been reached by all probes. If one probes deviates from the stability parameters (for instance there is a spike caused by interference), the countdown will be reset, and TQSoft will wait for all probes to come within the set parameters again before beginning the countdown again.

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Automatic vs Manual Calibration in TQSoft

If your pc is capable of communicating with a compatible thermal bath and temperature reference through, for example, an RS232 connection (or you have a unit that performs both funtions), TQSoft can take measurements at your setpoints from the probes under calibration and your temperature reference, detect stability, calibrate and then drive the temperature of the thermal bath up and down to the next set point. This allows you to set up your calibration parameters, begin calibration and continue with other tasks. You can then return to TQSoft once calibration has completed. The downside of this is that if there is an issue with the calibration (for instance interference prevents the probes stabilising) you will not be aware of it until you return to look at the screen.

Watch Automatic Calibration of Thermocouples Using TQSoft Here >

Manual calibration requires you to set your thermal bath to the required temperature, then enter the actual reading (usually from the thermometer) once everything has stabilised, and trigger the calibration procedure in TQsoft. Once this is completed, you then repeat the process for each point required. This allows you to monitor the stability and accuracy of the probes as the calibration proceeds, but requires you to be present to trigger each point (note you do not need to be present throughout, as the procedure will wait to be triggered once stability is reached).

Watch Manual Calibration of Thermocouples Using TQSoft Here >

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Interested in Purchasing a Temperature Calibrator?

See our full list of temperature calibrators on the Isopharm shop below, or contact us for more information