Internal freezer calibrations
Hi all, hoping someone can help me on inhouse freezer calibrations. we are under SQF stds. Our freezers are -18C and our product is 200litre drums of vegetable concentrate which will stay frozen for a good while. What i am trying to do is use dry ice with a nata certified thermometer against our freezer probes and record what our control panel reads. Issue is the dry ice will be at -78.5C which is no where near our -18C. Does anyone have a procedure or another way to go about doing this? Any help would be appreciated. :helpplease: Carol
Hi all, hoping someone can help me on inhouse freezer calibrations. we are under SQF stds. Our freezers are -18C and our product is 200litre drums of vegetable concentrate which will stay frozen for a good while. What i am trying to do is use dry ice with a nata certified thermometer against our freezer probes and record what our control panel reads. Issue is the dry ice will be at -78.5C which is no where near our -18C. Does anyone have a procedure or another way to go about doing this? Any help would be appreciated. :helpplease: Carol
Dear Carol,
I don’t quite see the problem. Assuming yr nata (whatever that means :smile:) thermometer is accurate, it should tell you the error as shown by the freezer’s own probe ? This assumes the (dual) measuring point is appropriate of course.
I assume yr primary query is that you wish to calibrate the nata thermometer. Hopefully a TC from convenience POV.
According to textbooks it is possible to do it yourself via appropriate frozen “mixes” but IMEX the hassle/frostbite is not worth it. :smile: The requirement should be commercially simple assuming 2-3 steps are available –
(1) you have ample physical access to yr in-built (TC) freezer probe. Looks like you do.
(2) you have access to an official / private organisation / company who will “standardize” yr “master” nata thermometer at any (ie by you) selected reference temperature(s). I imagine no problem to find in Australia. AFAIK, some companies use “black boxes”, others more “physical” techniques.
(3) Then you simply attach/contact yr calibrated master probe to the freezer probe. (or some, self-produced, sub-master).
For (2) I usually request something like -15degC, -21degC to span the target however the choice is up to you. Many companies will ask you whether you wish your current “zero” (assuming it is adjustable) to be adjusted by them so as to generate a best match calibration at any selected ref. point(s) or left unchanged. In either case they will report the final error between the indicated reading and “true” value (ie as per their own, NIST/nata (?) referenceable datum). Obviously the reported errors (or uncertainties) should be within a desired low value (eg hopefully negligible) or else the unit itself may require replacement.
Hopefully I haven’t misunderstood the request. :smile:
Rgds / Charles.C
Thank you Charles for your imput. NATA means National Association of Testing Authorities (a peak authority in Australia for the accreditation of inspection bodies). I may have confused you with how I approached the issue. I have a calibrated nata certified thermometer but I need to make sure that our control panel that say the freezers are running at -18C are correct so I need to take the freezer probe and a thermometer and measure the probe as close to -18 as possible and then check on the control panel to see if this is correct but the issue I have is an ice slurry will not get to -18C so I thought of using dry ice but that will give me a reading around -78.5C. I need to be able to use a solution around the temp that our freezers sit at to be accepted by our auditoring body (SQF).
Thank you Charles for your imput. NATA means National Association of Testing Authorities (a peak authority in Australia for the accreditation of inspection bodies). I may have confused you with how I approached the issue. I have a calibrated nata certified thermometer but I need to make sure that our control panel that say the freezers are running at -18C are correct so I need to take the freezer probe and a thermometer and measure the probe as close to -18 as possible and then check on the control panel to see if this is correct but the issue I have is an ice slurry will not get to -18C so I thought of using dry ice but that will give me a reading around -78.5C. I need to be able to use a solution around the temp that our freezers sit at to be accepted by our auditoring body (SQF).
Dear Carol,
Yes, that was how i understood yr post and attempted an answer. :smile:
Textbooks do answer yr last sentence via eutectic (IIRC) mixes but i recommend avoiding. IMEX the preparation was a real PITA.
Of course, if you are prepared to believe yr nata thermometer (calibrated at 0degC?) is "spot-on" at -18degC, no need to do anything special. Just subtract values and hopefully get close to zero.
i have little doubt that SQF would be satisfied with my method. I use it for calibrating Cold Room instruments running at ca. -18degC. Of course, a small external charge is involved.
(IMEX freezers usually run nearer -30degC.?? Maybe a language disconnect. :smile: )
Rgds / Charles.C
Hi Carol,
If your main aim is to check the calibration of your freezer temperature, you should not need a slurry, Taking a reading of the air temperature in the freezer itself at a close point to the probe, whilst someone else is checking the control panel (CATR display) should confirm this allowing perhaps for a 1 degree of temperature difference as a tolerance.
If you still need to calibrate probes in a solution, by adding either salt or sucrose to water you can lower the freezing point of water, you could probably find a table comparing concentration vs freezing point. But the air temperature test would involve less work and not mess with your freezer probe.
If you have a big freezer and want to ensure temperatures are consistent throughout take reading at various areas in the freezer to check for consistency, may require being lifted in a forklift cage.
Hi Carol,
If your main aim is to check the calibration of your freezer temperature, you should not need a slurry, Taking a reading of the air temperature in the freezer itself at a close point to the probe, whilst someone else is checking the control panel (CATR display) should confirm this allowing perhaps for a 1 degree of temperature difference as a tolerance.
If you still need to calibrate probes in a solution, by adding either salt or sucrose to water you can lower the freezing point of water, you could probably find a table comparing concentration vs freezing point. But the air temperature test would involve less work and not mess with your freezer probe.
If you have a big freezer and want to ensure temperatures are consistent throughout take reading at various areas in the freezer to check for consistency, may require being lifted in a forklift cage.
Dear ragga,
The problem, as i see it, is that most certified thermometers are not certified at -18degC and indeed IMEX will not be accurate at this low temperature. Hence a traceable calibration at the low temperature is necessary.
Temperature variations within the "freezer" are something else again IMO.
Nonetheless, perhaps you have a better understanding of the OP. :smile:
Rgds / Charles.C
Hi Carol,
If your main aim is to check the calibration of your freezer temperature, you should not need a slurry, Taking a reading of the air temperature in the freezer itself at a close point to the probe, whilst someone else is checking the control panel (CATR display) should confirm this allowing perhaps for a 1 degree of temperature difference as a tolerance.
If you still need to calibrate probes in a solution, by adding either salt or sucrose to water you can lower the freezing point of water, you could probably find a table comparing concentration vs freezing point. But the air temperature test would involve less work and not mess with your freezer probe.
If you have a big freezer and want to ensure temperatures are consistent throughout take reading at various areas in the freezer to check for consistency, may require being lifted in a forklift cage.
I agree, this is the best way to calibrate that the probe and the display are registering the correct temperature. You can purchase thermometers that are made for blood banks (this is just a suggestion https://us.vwr.com/s...umber=89095-678) that are traceable to NIST standards and have the bulbs in liquid or in glass beads in a bottle. You can let it equilibrate to the freezer temperature for several hours or overnight. Then you look at the display and record the temperature, then go in the freezer and look at the thermometer. The temperature will be stable for a few minutes due to the liquid/glass beads in the bottle even in your hand, so it will reflect the accurate temperature in the freezer. You can do this multiple times to map the hot spots and cold spots in your freezer as well, something that is very useful. It takes a little time, but this gives you a very accurate reading.
Place your certified thermometer in close proximity to the probes you are testing. If they both show the same temp your probes are correct. Just always make sure your calibration certificate is up-to-date.
I agree, this is the best way to calibrate that the probe and the display are registering the correct temperature. You can purchase thermometers that are made for blood banks (this is just a suggestion https://us.vwr.com/s...umber=89095-678) that are traceable to NIST standards and have the bulbs in liquid or in glass beads in a bottle. You can let it equilibrate to the freezer temperature for several hours or overnight. Then you look at the display and record the temperature, then go in the freezer and look at the thermometer. The temperature will be stable for a few minutes due to the liquid/glass beads in the bottle even in your hand, so it will reflect the accurate temperature in the freezer. You can do this multiple times to map the hot spots and cold spots in your freezer as well, something that is very useful. It takes a little time, but this gives you a very accurate reading.
Thank you for your imput of my question but I'm still a bit confused as I am thinking that by checking the air temp at several points throughout our large freezer and comparing to the control panel is a monitoring stage only and not actually a calibration of the freezer probes. Also thinking that SQF (auditing body) wouldn't accept this as a calibration of a CCP.
Place your certified thermometer in close proximity to the probes you are testing. If they both show the same temp your probes are correct. Just always make sure your calibration certificate is up-to-date.
Yes this is the way that I feel would be accept by our auditing body (SQF) but I think that they would want me to check at -18C as that is the temp our freezers sit on but its getting a solution to get to -18C that I'm having the issue with. I personally feel that because of our product being 200L drums of concentrate that if I calibrate at OC that it will not be a problem but I do have to conform to our quality system
Dear Carol,
Calibration to achieve a “master” (certified) unit is typically done, as you originally discussed, by use of a standard reference temperature source(s). AFAIK, an acceptable reference source for -18degC is not readily accessible to the average processor. It is available to the professional calibration services as implemented per my previous post. Hence > money.
I have never had a an auditorial problem by generating multiple, portable, thermocouple (TC) “sub-masters” from a master unit for use in a processing facility at temperatures ranging from -18degC to 100degC.
I have never had an auditorial problem by using portable sub-masters to “calibrate” general purpose, fixed equipment probes. (Certain critical FS locations, eg retort thermometers, would probably be exceptions).
IMEX, for a master unit, most FS auditors expect to see a documented calibration traceable to, for example NIST, dated not > 12 months back from audit date. Sub-masters typically require (documented) daily-monthly calibration depending on, for example, temperature / location of use / accuracy required.
TCs are IMO unbeatable for convenience in use / cost but they have accuracy limitations (eg see the manual).
Perhaps a little more info. might help to focus yr query, eg -
What kind of master (certified) thermometer are you using ? eg, Hg, thermocouple (TC) Cu/Constantan
What temperature(s) is the master (certified) thermometer calibrated at ?
When was yr master (certified) thermometer last calibrated ?
Rgds / Charles.C
Dear All,
I'm using wireless temperature monitoring for our freezer. We placed 2 data logger for measuring air temperature inside the freezer and also simulated product core temperature.
The freezer temperature is observing online via laptop which I can download and print out the data.
Here is my questions:- :helpplease: :helpplease:
1- If I want to do calibration, I shall calibrate the freezer or the data logger?
2- If I want to do internal calibration to the freezer (more than 20 units) what are the methods I can do or follow? Thinking to have set of separated data logger that I can make as master calibration however I'm not very sure acceptable or not from auditor point of view.
3- If the freezer is one of the CCP. Is it accepted by auditor if the simulated product core temperature I present as the CCP record? or I still need to do manually check the product core temperature?
Hopefully someone able to clarify this thing for me.
Thank you
Mufar
Dear All,
I'm using wireless temperature monitoring for our freezer. We placed 2 data logger for measuring air temperature inside the freezer and also simulated product core temperature.
The freezer temperature is observing online via laptop which I can download and print out the data.
Here is my questions:- :helpplease: :helpplease:
1- If I want to do calibration, I shall calibrate the freezer or the data logger?
2- If I want to do internal calibration to the freezer (more than 20 units) what are the methods I can do or follow? Thinking to have set of separated data logger that I can make as master calibration however I'm not very sure acceptable or not from auditor point of view.
3- If the freezer is one of the CCP. Is it accepted by auditor if the simulated product core temperature I present as the CCP record? or I still need to do manually check the product core temperature?
Hopefully someone able to clarify this thing for me.
Thank you
Mufar
Hi Mufar,
(1) I’m not sure what you mean by “calibrate the freezer” ? Can you clarify ? The terminology is variously used, eg see this post/thread-
http://www.ifsqn.com...ion/#entry97634
(2) See (1).
(3) An auditor will probably expect to see the theoretical/practical validation of the simulation.