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Ieatcookies

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Posted 12 May 2020 - 02:21 PM

Hi, 

 

Quick question about probe verification. 

 

I would like to purchase a reference probe for the company and verify weekly temperatures with boiling and hot water comparing it to reference probe. Are there any requirements for a ref probe to be fulfilled (except the obvious that it must be calibrated and certified)?

 

Also, if we do verify the freezers temperatures with probes, what would be the temperature check to reaach the scope? freezer is approximately -18 and boiling water only 0. how to challenge the -18 temperature? 

 

 



Ieatcookies

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Posted 12 May 2020 - 02:48 PM

sorry, *with boiling and iced water



Xoinks

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Posted 12 May 2020 - 03:53 PM

Hi, 

 

Quick question about probe verification. 

 

I would like to purchase a reference probe for the company and verify weekly temperatures with boiling and hot water comparing it to reference probe. Are there any requirements for a ref probe to be fulfilled (except the obvious that it must be calibrated and certified)?

 

Also, if we do verify the freezers temperatures with probes, what would be the temperature check to reaach the scope? freezer is approximately -18 and boiling water only 0. how to challenge the -18 temperature? 

 

1)  Reference probe/thermometer should be NIST traceable.  We purchase a new one each year as that's less expensive than sending it out for calibration verification annually, albeit more wasteful.

 

2)  0F calibration verification would be appropriate for assuring the thermometer is accurate around -18, as you use the standard reference closest to your target.  This is further justified as usually in freezer environments, getting an exact reading isn't highly critical - +/- 1 or 2 degrees is generally appropriate and that variation is not going to impact quality or safety.   



Ryan M.

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Posted 12 May 2020 - 04:27 PM

Be sure to calibrate at the temperature of normal usage, or as close as possible.

 

Depending on the NIST thermometer you purchase it isn't always less expensive to buy a new one each year.  Thermco offers calibration services and the normal 3 point calibration service we do on our NIST thermometer is ~$100, plus shipping, and a new one would be about $150.  It is basically a wash, but saves waste.  My predecessor bought a new one each year and when we cleaned out the lab we had 12 of them on hand to deal with and dispose of which wasn't cheap.



MsMars

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Posted 12 May 2020 - 04:51 PM

Be sure to calibrate at the temperature of normal usage, or as close as possible.

 

Depending on the NIST thermometer you purchase it isn't always less expensive to buy a new one each year.  Thermco offers calibration services and the normal 3 point calibration service we do on our NIST thermometer is ~$100, plus shipping, and a new one would be about $150.  It is basically a wash, but saves waste.  My predecessor bought a new one each year and when we cleaned out the lab we had 12 of them on hand to deal with and dispose of which wasn't cheap.

 

Depends on what type of reference thermometer you purchase.  It is possible to purchase a digital NIST reference thermometer if you don't have the means to deal with disposal of a mercury-filled thermometer, and is sometimes cheaper than annual calibration. 



Charles.C

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Posted 12 May 2020 - 04:54 PM

Hi, 

 

Quick question about probe verification. 

 

I would like to purchase a reference probe for the company and verify weekly temperatures with boiling and hot water comparing it to reference probe. Are there any requirements for a ref probe to be fulfilled (except the obvious that it must be calibrated and certified)?

 

Also, if we do verify the freezers temperatures with probes, what would be the temperature check to reaach the scope? freezer is approximately -18 and boiling water only 0. how to challenge the -18 temperature? 

 

Hi leatcookies,

 

Actually the probe is only half the unit.

 

You omitted to mention what kind of thermometer you are purchasing.

 

The choice may also relate to yr intended usage / desired accuracy. I invested in one relatively expensive unit which I reserved as a "master"  for internally  "certifying" other "sub-master" units.

 

afaik most units are pre-calibrated/documented at melting ice temperature,

 

IMEX, for thermocouples, the accuracy across the range 0-100degC can depend on the cost. A unit with a resettable zero may be worthwhile

 

IMEX. measurements at ca -18degC will likely require having the unit separately certified at that temperature. (I attempted to prepare suitable reference solutions but ultimately concluded too much trouble). Professional calibration at specific temperatures is often not particularly expensive.

 

I personally found that using steam was operationally more reliable than boiling water. Just my opinion.


Kind Regards,

 

Charles.C





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