I am looking for suggestions on how to calibrate thermometer'sfor my department ultra- low freezer. I say that I should test my NIST and testthermometer in the same medium (i.e. glycol) but my laboratory managerdisagrees. My other question is what is the acceptable difference between mytraceable NIST and my test thermometers at -70?

I have had such dilemmas in the past with ultra low thermometers and trying to calibrate them that now I buy a new one every year. It comes with a NIST certificate. Costs around $40, so well worth the money.

I do exactly what Terri does. Much, much easier.

I have been placing my NIST thermometer into the freezer with the thermometer I'm qualifying for use, and use a +/- of 1C as my acceptability parameter. It has worked so far. It does take a little while to get from room temp to the -70C range but it does work. We are in the process of converting to a wireless monitoring system which sends us NIST validated probes on an annual basis. That will save a lot of time.

QCDan,

What company do you use for wireless temp monitoring?

We just finished the install with Checkpoint wireless. I'm still working on getting the probes placed in the appropriate spots so that we can get a consistent temperature reading. We are about a month away from starting our validation of the system.

We do the same as Terri, buy a new one every year.

We also do the same as Terri, buy a new one each year.

(Please note I am the Operations Director and Deputy Quality & Technical Manager for ISO/IEC 17025:2005 at Tempsys which makes the CheckPoint Wireless Monitoring System)

As has been mentioned, having a new or re-calibrated NIST traceable probe sent to you is the simplest solution and definitely worth $40. Calibrating probes in an ice bath for 0C is fine however I don't recommend trying to perform comparative measurements for -70C unless you're familiar with measurement uncertainty and calibration procedures. Our probes are spec'd at +/- 0.5C although Dan's +/- 1.0C should be fine since most departments set their low/high alarms at -80/-60.

Mike - Good to know.

Edited August 29, 201212 yr by AMcCord