Is the Ice Bath-Boiling water method an acceptable calibration for thermometers?

Per the SQF do you need a calibrated thermometer, or can you use the ice bath/boiling method if you can accept a +/- variance of 2 deg F?

Equipment shall be calibrated against national or international reference standards and methods or to an accuracy appropriate to its use. In cases where standards are not available, the site shall provide evidence to support the calibration reference method applied.

Directly from the code---there is no reason you cannot use the ice bath method or boiling water method

 

Here, we have 1 calibrated thermometer we send out annually for certification and use that as our reference standard 

Per the SQF do you need a calibrated thermometer, or can you use the ice bath/boiling method if you can accept a +/- variance of 2 deg F?

As per the quote in Post 2 it may depend on the context.

 

Also from SQF9 -

Calibration shall be performed according to regulatory requirements and/or to the equipment manufacturers’ recommended schedule.

 

and from Guidance to SQF 8.1

 

Thermometers can be calibrated against boiling water or ice-water if these approximate the temperatures the thermometer is required to measure when in use.

(in practice there are usually some Procedural specificities to the above)

 

IMEX last line of previous Post is auditorially less argumentative unless temp. measuring instrument is not readily accessible, eg built into equipment or high accuracy is not critical.

We check our thermometers weekly using the ice/water method. We have a couple of thermometers that are adjustable.
We also have a MiG thermometer that we judge the adjustable ones against and THAT gets sent out annually for calibrations.

Per the SQF do you need a calibrated thermometer, or can you use the ice bath/boiling method if you can accept a +/- variance of 2 deg F?

Hi 2xmahi,

Ice bath/boiling water method can be used as  per Canadian inspection Agency if you don't have reference thermometer but tolerance is +_ 0.5 only.

 link is also shared below. Just go through that and let me know if you have any questions.

1. Using the ice point and the boiling point method: Calibrate the thermometer at both points. Use this method only when a reference thermometer is not available.
   • Ice Point Method:
     • Fill a large glass with crushed ice. Add clean tap water until the glass is full and stir well.
     • Let the mixture stabilize for 4 to 5 minutes, then insert the thermometer stem or probe in the ice water mixture so that the entire sensing area is submerged. Do not let the stem of the thermometer or probe touch the sides or bottom of the glass.
     • Wait at least 2 minutes or until the reading stabilizes. The temperature on the thermometer should read 0°C ±0.5°C. Record the temperature reading.
   • Boiling Point Method:
     • Bring clean tap water to a full boil in a deep container (greater than 25 cm or 10 inches)
     • Put the thermometer stem or probe into the boiling water so that the sensing area is completely submerged. Do not let the stem or probe touch the bottom or sides of the container.
     • Wait at least 2 minutes or until the reading stabilizes. The temperature should read 100°CFootnote 1 ±0.5°C. Record the temperature reading.

Corrective Action

A thermometer outside of the tolerance should be recalibrated and rechecked to verify accuracy. If it cannot be calibrated then it should be discarded in an appropriate manner and replaced.

https://inspection.c...3/1540302234709

 

Thanks

Hi Namishka,

 

A few general comments on cfia method.

 

(1) ice should have certain "controlled" characteristics, eg finely crushed.

(2) An insulated flask, eg Dewar, is preferred.

(3) Many users implement a final, theoretically correct, adjustment based on the determined error at the standard points. Some contractors (and instrument manuals) can reset the instrument (if functionally possible) to read "100%" correct  at a given individual temperature.

(4) As noted by SQF, working at 0degC and 100degC is illogical if using instrument at, say. 44degC, unless the error is constant across the temperature range which is unlikely for TCs.

(5) IMEX some thermocouples give variable results in boiling water, possibly due errors within connections. I use steam albeit this has its own sensitvities.

 

IMEX it is always preferable to obtain at least one externally calibrated unit if possible where the test conditions can be well-controlled plus an evaluation of instrument reliability is usually also provided. The ice-point method is undeniably of attractive simplicity but the results can sometimes be surprisingly inconsistent between operators.

Charles, if you follow what our National Food Safety Regulator says (at least in Canada) you'd be hard pressed to find an auditor who would argue

 

However, there are lots of online resources for following the ice bath method

https://www.maricopa...Thermometer-PDF

 

https://www.michigan...Thermometer.pdf

 

https://us.flukecal....eres-better-way

 

Depending on your individual process (just how accurate you REALLY need to be), ice bath may be sufficient as a means of calibration

We check our thermometers weekly using the ice/water method. We have a couple of thermometers that are adjustable.
We also have a MiG thermometer that we judge the adjustable ones against and THAT gets sent out annually for calibrations.

 

To Setanta's point, equipment calibration and equipment verification of calibration often get thrown around interchangeably. We follow the same process of using a calibrated thermometer to check or verify our operating thermometers against the defined standard (boiling water, ice water, etc.). This is verifying the thermometer's calibration, not calibrating the thermometer. It may not seem like a big difference, but auditors often times challenge the language surrounding equipment verification and calibration.

Charles, if you follow what our National Food Safety Regulator says (at least in Canada) you'd be hard pressed to find an auditor who would argue

 

However, there are lots of online resources for following the ice bath method

https://www.maricopa...Thermometer-PDF

 

https://www.michigan...Thermometer.pdf

 

https://us.flukecal....eres-better-way

 

Depending on your individual process (just how accurate you REALLY need to be), ice bath may be sufficient as a means of calibration

 

Hi Scampi,

 

I agree the accuracy is relevant but with all due respect -

 

First two refs are illustrations for dial gauges. (+ a wrench !)

 

Last link is presumably for most production laboratories an External Calibration.

 

PS - from hearsay I can add a couple more thoughts to the 3rd reference -

 

(1) the environment is required to be maintained at a controlled temperature.

(2) the ice must be crushed to a specified fineness for consistent results.

 

PPS - not my area of expertise but the dry-well method also seems to involve signifiicant care -

 

https://us.flukecal....ry-well-tempera

 

@foodguy - Labelling the externally calibrated unit as "Master" and the "calibrated against" units as "Sub-Masters" usually overwhelms most auditors' tendency to quibble over semantics IMEX.

 

Calibration - A set of operations that establish, under specified conditions, the relationship between values of quantities indicated by a measuring instrument or measuring system, or values represented by a material measure or reference material, and the corresponding values realised by standards.

You are correct, that was imprecise wording. We send our thermometer out to have it's accuracy certified.

Calibration checks
The site needs to establish the method by which the precision and accuracy of equipment is verified.
This must include:
.....
the method to be used (which must, where possible, be traceable to a recognised standard, e.g. use of a master calibration thermometer that has a certified test certificate traceable to a national standard).

(BRC)