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kgonzalez

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Posted 06 March 2018 - 01:58 PM

I have what should be a silly question, but apparently isn't.

 

I've recently started working for a new company (fresh cut produce). None of our thermometers are certified, as we have no critical temperature checks. We record wash water temperatures for which we have set parameters, but from what I understand that's a quality/shelf-life check. We still do daily thermometer checks with an ice bath to ensure our measurements are accurate (our dial thermometers can be manually adjusted if found out of spec).

 

I was alarmed to discover that QA keeps and uses a large glass thermometer to verify the temperature of the ice bath. Although it is kept well away from production, it seemed to me an unnecessary item (risk) to have. The response I got from the QA manager is that an auditor challenged us on the properly prepared ice bath having a "known" temperature.

 

Does anyone know where I might find scientific evidence to validate the temperature of an ice bath for thermometer checks?



sarah2014

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Posted 06 March 2018 - 02:19 PM

no they do this method for thermometer calibration / Thermometer calibration must take place daily against NIST traceable calibrated thermometer.



sarah2014

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Posted 06 March 2018 - 02:21 PM

 plus the NIST traceable thermometer cannot be removed from the metal armor and is to be kept in the QA office when not in use.



kgonzalez

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Posted 06 March 2018 - 02:55 PM

Under FSMA, all I can find is 117.40(f) "Instruments and controls used for measuring, regulating, or recording temperatures...that control or prevent the growth of undesirable microorganisms in food must be accurate and precise or adequately maintained, and adequate in number for their designated uses."

 

And the SQF code (which we're moving to), states, "Equipment shall be calibrated against national or international reference standards and methods or to accuracy appropriate to its use. In cases where standards are not available, the site shall provide evidence to support the calibration reference method applied."

 

Both standards seem to suggest that, since we're not monitoring temperatures to control or prevent growth, an ice bath calibration would be sufficiently accurate. Additionally, our glass thermometer is not NIST traceable, nor does it have metal armor - we've not been challenged on any of that.

 

Honestly, I trust the ice bath more than an NIST calibrated thermometer. I previously used the ice bath to check calibrated thermometers, and those suckers could read at 34*F for months. Or 30*F. Or anywhere in between. They only get calibrated once per year, we used the ice to make sure they were still accurate the rest of the days of the year for a reason.



sarah2014

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Posted 06 March 2018 - 03:14 PM

Create water and ice slush mix (use crushed ice).

 

Allow to the mixture to stand for five minutes and fully equilibrate.

 Place the NIST traceable calibrated thermometer into the mixture and allow for temperature reading to stabilize. Temperature should read 32 °F.

 Place thermometers to calibrate into the mixture. Allow for the temperature reading to stabilize.

 

 Record all readings in appropriate form mentioned above.

 

Compare the results of the non-certified thermometers against the NIST traceable certified thermometer.

 

The result must be 30°- 34° F. (32 + 2° F). Account for NIST thermometer calibration deviation.



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Scampi

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Posted 06 March 2018 - 03:33 PM

Let's seperate daily/weekly verification from calibration

 

A certified thermometre should be onsite that everything else is CALIBRATED against according to your frequency.

 

Daily/weekly checks could be done against either ice slurry or boiling water (I allow 1 degree C either way to account for small discrepancies)


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MsMars

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Posted 06 March 2018 - 06:10 PM

If you think that the NIST-certified glass thermometer poses too much of a risk (glass breakage perhaps?), there are plenty of plastic-type NIST-certified thermometers available.  We purchase several from Thermoworks - many have the option of NIST calibration with certificate.  

 

Ice bath calibration checks are pretty much the norm for checking thermometers against an NIST-certified thermometer, at least in my experience.  You would still need to check your thermometers with an ice bath and the NIST thermometer. You can't really "scientifically validate" the temperature of an ice bath (as it varies based upon several factors, hence the variation you've seen with your readings ~34 degrees), but can rely on the NIST thermometer being able to read the most accurate temperature of the bath and then checking your production thermometers against the reading of the NIST thermometer to make sure they are within X degrees of the NIST thermometer's reading. 



Saravudh

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Posted 22 August 2019 - 01:58 AM

Create water and ice slush mix (use crushed ice).

 

Allow to the mixture to stand for five minutes and fully equilibrate.

 Place the NIST traceable calibrated thermometer into the mixture and allow for temperature reading to stabilize. Temperature should read 32 °F.

 Place thermometers to calibrate into the mixture. Allow for the temperature reading to stabilize.

 

 Record all readings in appropriate form mentioned above.

 

Compare the results of the non-certified thermometers against the NIST traceable certified thermometer.

 

The result must be 30°- 34° F. (32 + 2° F). Account for NIST thermometer calibration deviation.

Dear Sarah2014,

 

Thanks for your information and i would like to know about the ratio between water and crushed ice to make ice bath.

Can you advise me. Thank you in advance.

 

Best Regards,

Saravudh



Charles.C

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Posted 22 August 2019 - 07:22 AM

Hi Saravudh,

 

IMEX Thermometer Calibration can require considerable thought as to what one's observed measurements actually mean.

 

IMO it is preferable to select a "Master" thermometer, have it officially, ie NIST traceable, lab. certified at one's temperatures of interest so as to determine it's correction factors/accuracy then use it to accept/reject other units intended as sub-masters.

 

IMEX, despite what many texts seem to expect, many/most thermometers will not show 0.0degC in a melting- ice bath. 2 possible causes are (a) specification accuracy of thermometer, (b) actual temperature of the ice-bath.

 

An official certification quantitatively answers the (a) factor above.(eg see Table 1 in 5th pdf below).

 

Just as an aside, my Master thermometer was certified to indicate 0.1degC in the reference ice bath however it always showed 0.2-0.3 in my ice baths. The certifying Company responded that my ice/technique/environment would be unlikely to match their controlled setup (eg particle size of ice used). (Also note caveat "4" in 2nd pdf below).

 

Re - ice-bath preparation, I have selected 4 versions you can compare - (i) a quick but reasonably accurate method, (II) a commercial, more elaborate Procedure, (III) a reference level methodology (2 examples) -

 

Attached File  rapid ice bath.pdf   980.07KB   41 downloads

Attached File  more elaborate ice bath.pdf   519.07KB   34 downloads

Attached File  Reference Ice-bath.pdf   790.5KB   38 downloads

Attached File  Canadian ref. ice bath,TE-LP-001.pdf   69.09KB   26 downloads

 

I have also added one more calibration file which has some useful comments and a rather neat usage Table1.

 

Attached File  Calibration-of-thermometers.pdf   128.37KB   90 downloads


Kind Regards,

 

Charles.C


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Saravudh

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Posted 26 August 2019 - 02:06 AM

Hi Saravudh,

 

IMEX Thermometer Calibration can require considerable thought as to what one's observed measurements actually mean.

 

IMO it is preferable to select a "Master" thermometer, have it officially, ie NIST traceable, lab. certified at one's temperatures of interest so as to determine it's correction factors/accuracy then use it to accept/reject other units intended as sub-masters.

 

IMEX, despite what many texts seem to expect, many/most thermometers will not show 0.0degC in a melting- ice bath. 2 possible causes are (a) specification accuracy of thermometer, (b) actual temperature of the ice-bath.

 

An official certification quantitatively answers the (a) factor above.(eg see Table 1 in 5th pdf below).

 

Just as an aside, my Master thermometer was certified to indicate 0.1degC in the reference ice bath however it always showed 0.2-0.3 in my ice baths. The certifying Company responded that my ice/technique/environment would be unlikely to match their controlled setup (eg particle size of ice used). (Also note caveat "4" in 2nd pdf below).

 

Re - ice-bath preparation, I have selected 4 versions you can compare - (i) a quick but reasonably accurate method, (II) a commercial, more elaborate Procedure, (III) a reference level methodology (2 examples) -

 

attachicon.gif rapid ice bath.pdf

attachicon.gif more elaborate ice bath.pdf

attachicon.gif Reference Ice-bath.pdf

attachicon.gif Canadian ref. ice bath,TE-LP-001.pdf

 

I have also added one more calibration file which has some useful comments and a rather neat usage Table1.

 

attachicon.gif Calibration-of-thermometers.pdf

Dear Charles.C,

 

Thank you very much for good informations.

 

Best Regards,

Saravudh






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