14 replies to this topic

[clover]

Hi all, 

 

just have a few questions about internal calibration for equipments: - 

 

A) Thermometers. 

 

To calibrate a simple probe thermometer is pretty straightforward but what's the proper way to calibrate a UV infrared thermometer as I understand it only measures the temperature of external surface of an item? 

 

B) Weighing Scales. 

 

Let's say (Digital) Weighing Scale A has a min = 40g and max = 30kg - is it necessary to verify that I the scale could measure both min & max accurately? What should be the frequency/scale of measurement be like? Every 10kg? 

 

And I assume that for a digital weighing scale with a max of 5kg the measurement would be 1,2,3,4,5kg? 

 

If anyone have any calibration SOP to share, that would be great as it's my first. Thanks. 

 

 

[QAGB]

Hi all, 

 

just have a few questions about internal calibration for equipments: - 

 

A) Thermometers. 

 

To calibrate a simple probe thermometer is pretty straightforward but what's the proper way to calibrate a UV infrared thermometer as I understand it only measures the temperature of external surface of an item? 

 

B) Weighing Scales. 

 

Let's say (Digital) Weighing Scale A has a min = 40g and max = 30kg - is it necessary to verify that I the scale could measure both min & max accurately? What should be the frequency/scale of measurement be like? Every 10kg? 

 

And I assume that for a digital weighing scale with a max of 5kg the measurement would be 1,2,3,4,5kg? 

 

If anyone have any calibration SOP to share, that would be great as it's my first. Thanks. 

 

 

Hi Clover,

 

A) I don't know if you can calibrate an infrared (IR) thermometer in-house. I would suggest you have a master thermometer that you get calibrated externally, and compare your results from the IR thermometer to the master. You may also be able to get the IR thermometer calibrated externally as well, if you find the results are off; but I don't think I'd ever want to use it as a master.

 

B) Analytical and table top balances should come with a manual. In the manual, you will find the calibration weight needed to calibrate your scales. You can do verifications however you'd like, but I tend to try to use weights for verifications that would be near the range of the scale's intended use. As an example, if you are using the scale to weigh products in the 1-5 kg. range, you can verify with a weight somewhere in that range. Also, be sure the weights you use are accurate to the degree you need them. Calibration weights for lab scales for very accurate measurements are usually Class 0-7 (ASTM) with 4 being the class you would not want to go under for accurate measurements. Also you may find weights in OIML certification classes E,F, and M, and you would want to stay within classes E or F (F being the least accurate of the two) for lab scales.

 

If you need floor scales (scales for pails, drums, totes, sacks of product), I would definitely suggest you have an external company actually calibrate those annually. You can get 11 - 22 kg calibration weights to verify your floor scales periodically, and call the company if the readings on the scales are out of tolerance.

 

 

QAGB

[QAGB]

Hi Clover,

 

A) I don't know if you can calibrate an infrared (IR) thermometer in-house. I would suggest you have a master thermometer that you get calibrated externally, and compare your results from the IR thermometer to the master. You may also be able to get the IR thermometer calibrated externally as well, if you find the results are off; but I don't think I'd ever want to use it as a master.

 

B) Analytical and table top balances should come with a manual. In the manual, you will find the calibration weight needed to calibrate your scales. You can do verifications however you'd like, but I tend to try to use weights for verifications that would be near the range of the scale's intended use. As an example, if you are using the scale to weigh products in the 1-5 kg. range, you can verify with a weight somewhere in that range. Also, be sure the weights you use are accurate to the degree you need them. Calibration weights for lab scales for very accurate measurements are usually Class 0-7 (ASTM) with 4 being the class you would not want to go under for accurate measurements. Also you may find weights in OIML certification classes E,F, and M, and you would want to stay within classes E or F (F being the least accurate of the two) for lab scales.

 

If you need floor scales (scales for pails, drums, totes, sacks of product), I would definitely suggest you have an external company actually calibrate those annually. You can get 11 - 22 kg calibration weights to verify your floor scales periodically, and call the company if the readings on the scales are out of tolerance.

 

 

QAGB

 

I should also mention that for ASTM classes, 0 is the class with the most accuracy, and 7 is the class with least accuracy. You'd want to stay within classes 0-4.

 

For OIML classes, E is the class with most accuracy, and M is the class with least accuracy. You'd want to stay within classes E & F.

 

QAGB

[Charles.C]

Hi Clover,

 

A few comments,

 

It somewhat depends as per previous post if you are talking about calibration by an inhouse-master / sub-master unit or an official external calibration unit.

 

I agree with QAGB regarding method for checking accuracy of balances – across the range and particularly in area where the balance is typically used. Usually balances have a manufacturer specification for accuracy across their range.

 

For internal purposes, IMO the nature of yr process requirements will define –

 

(a) the necessary range of  the routine measuring unit  

(b) the necessary accuracy/resolution to be provided by the routine measuring unit.
 

(a,b) will then define the minimal requirements of the Procedure to be used for Calibration of the equipment.

 

Calibration procedures for IR thermometers have been discussed previously on this forum. They looked to be not simple to me. (no personal experience).

 

afaik a UV thermometer is not used to measure temperature ? (never seen one).

 

I suspect the equipment available for master calibration equipment may vary with  location. The items used are presumably minimally required to be certified/accredited and traceable. The only visual difference I have noted regarding balance checkweights used internally by myself and those of the balance supplier is the material, bronze versus stainless steel.

 

IMEX metrology can be a complicated science although it looks simple.

 

You may need to give more details of yr operation to get fully relevant feedback.

[clover]

Hi Clover,

 

A few comments,

 

It somewhat depends as per previous post if you are talking about calibration by an inhouse-master / sub-master unit or an official external calibration unit.

 

I agree with QAGB regarding method for checking accuracy of balances – across the range and particularly in area where the balance is typically used. Usually balances have a manufacturer specification for accuracy across their range.

 

For internal purposes, IMO the nature of yr process requirements will define –

 

(a) the necessary range of  the routine measuring unit  

(b) the necessary accuracy/resolution to be provided by the routine measuring unit.
 

(a,b) will then define the minimal requirements of the Procedure to be used for Calibration of the equipment.

 

Calibration procedures for IR thermometers have been discussed previously on this forum. They looked to be not simple to me. (no personal experience).

 

afaik a UV thermometer is not used to measure temperature ? (never seen one).

 

I suspect the equipment available for master calibration equipment may vary with  location. The items used are presumably minimally required to be certified/accredited and traceable. The only visual difference I have noted regarding balance checkweights used internally by myself and those of the balance supplier is the material, bronze versus stainless steel.

 

IMEX metrology can be a complicated science although it looks simple.

 

You may need to give more details of yr operation to get fully relevant feedback.

Hi Charles, 

 

thanks for always faithfully replying to my questions. And sorry for the delayed reply as work has been busy. 

 

You kinda lost me at your first sentence. Inhouse-master? Sub-master unit? What does it mean and their difference? 

Yes QAGB is right in that it would only make sense to calibrate them within the range of the scale's intended use. No, we're not a lab just a small central kitchen and have decided to outsource calibration of weighing scales to third party instead. 

 

Sorry for the typo. I meant infrared thermometer, not UV. It’s currently used to measure our walk-in chiller and freezers. 

[Andy_Yellows]

Hi Clover,

 

We use IR Guns at my place and calibrate them by freezing a cup of water until the surface turns to ice (takes about an hour at -18°C). A reference needle probe is then put in the ice and should read 0.0°C. The IR Gun is then shot with the laser aimed directly down the hole made by the needle and should give the same reading (roughly). Our tolerance is +/- 0.5°. 

 

Hope this helps

 

Andy

[clover]

Hi Clover,

 

We use IR Guns at my place and calibrate them by freezing a cup of water until the surface turns to ice (takes about an hour at -18°C). A reference needle probe is then put in the ice and should read 0.0°C. The IR Gun is then shot with the laser aimed directly down the hole made by the needle and should give the same reading (roughly). Our tolerance is +/- 0.5°. 

 

Hope this helps

 

Andy

Hi Andy, 

 

that's interesting to know. I presume you placed the reference needle probe before freezing? As it's surely not possible to punch a hole into the hard ice with that needle probe. I shall try this method and see if it works. Does it matter how high/low the IR gun is held from the hole?

I have a few IR thermometers and found that their temperature reading differ quite a lot by 5-8C (when reading the same temperature spot). I'm not sure why, and I'm not sure how to rectify this. They're relatively new, bought it half a year ago, had their batteries changed. Manufacturer specifications states that accuracy is "+/- 2% of reading or 2C whichever is greater". 

A side question : how frequent should IR thermometers be calibrated? Yearly, half yearly or monthly? 

[Andy_Yellows]

Clover,

 

What we actually do is just allow the top of the water to freeze over rather than turning the entire contents of the cup into an iceberg. Like I said it normally takes about an hour to get it to that point. Then we do just bang a hole through with the needle (goes through pretty easily) although my old boss used to tell me off for doing it! I normally hold the gun between an inch and 2 inches from the ice. We calibrate our gun weekly.

As for your question regarding different guns giving different readings I found this to be the case as well. We bought a new one and the colder the surface being probed the more it differed from the reading given by the old gun. On calibration it showed the new one was faulty, so if you're using the same brand that we did then there was perhaps a manufacturing issue there at the time.

 

Regards,

 

Andy

[Charles.C]

Hi Andy, 

 

that's interesting to know. I presume you placed the reference needle probe before freezing? As it's surely not possible to punch a hole into the hard ice with that needle probe. I shall try this method and see if it works. Does it matter how high/low the IR gun is held from the hole?

I have a few IR thermometers and found that their temperature reading differ quite a lot by 5-8C (when reading the same temperature spot). I'm not sure why, and I'm not sure how to rectify this. They're relatively new, bought it half a year ago, had their batteries changed. Manufacturer specifications states that accuracy is "+/- 2% of reading or 2C whichever is greater". 

A side question : how frequent should IR thermometers be calibrated? Yearly, half yearly or monthly? 

 

hi clover,

 

IIRC, "official' SOPs for calibrating IRs have been previously posted on the forum. I  think these were dissimilar to Andy's method but maybe his was from an instrument  manual.

 

i believe it is accepted that IR instruments are typically less accurate than thermocouple probes but they are obviously convenient for certain jobs if close accuracy is not necessary. And possibly, if appropriately calibrated when accuracy is required, (thermocouples can also be unreliable if, for example, used for temperatures distant from their calibration points).

 

re post 5, a master temperature-measuring unit such as a thermocouple is one which has a satisfactory, current, traceable, calibration certificate and is being used in a situation  appropriate to that of the calibration. This is typically a purchased unit which has a current, external calibration certificate containing data acquired under controlled conditions  for certain instrumental characteristics. (examples exist on this forum).

 

A sub-master is a random unit whose reading satisfactorily agrees with the readings shown by the master unit. This is typically an in-house calibration.

 

"satisfactory" depends on the requirements of the application and the intrinsic characteristics of the unit, eg accuracy/confidence/uncertainty of the displayed readings.

 

Metrology is not a simple topic.

[clover]

Clover,

 

What we actually do is just allow the top of the water to freeze over rather than turning the entire contents of the cup into an iceberg. Like I said it normally takes about an hour to get it to that point. Then we do just bang a hole through with the needle (goes through pretty easily) although my old boss used to tell me off for doing it! I normally hold the gun between an inch and 2 inches from the ice. We calibrate our gun weekly.

As for your question regarding different guns giving different readings I found this to be the case as well. We bought a new one and the colder the surface being probed the more it differed from the reading given by the old gun. On calibration it showed the new one was faulty, so if you're using the same brand that we did then there was perhaps a manufacturing issue there at the time.

 

Regards,

 

Andy

Hi Andy, 

 

I see. Yah, I guess you could punch a hole into the ice if it's thin enough. Weekly calibration seems kinda excessive? Why did you decide to do it weekly? 

 

Good to know that there are people with the same problem! What a relief. So, did you throw the faulty one away or get it repaired? 

 

On a different note, how often do you calibrate your walk-in chillers, walk-in freezers, chiller/freezer trucks? I'm thinking that calibration of these cold stores might not be necessary if I have a master IR thermometer to calibrate them. Meaning to say, the temperature displayed on the IR should match the temperature displayed on the temperature LED panel. If there's a vast difference between the two, it would then be appropriate to get the coldroom calibrated. 

 

Also, this may potentially be a silly question, but can maintenance/servicing = calibration, with regards to cold room/cold storage? 

 

Cheers, 

Clover

[Andy_Yellows]

Hi Andy, 

 

I see. Yah, I guess you could punch a hole into the ice if it's thin enough. Weekly calibration seems kinda excessive? Why did you decide to do it weekly? 

 

Good to know that there are people with the same problem! What a relief. So, did you throw the faulty one away or get it repaired? 

 

On a different note, how often do you calibrate your walk-in chillers, walk-in freezers, chiller/freezer trucks? I'm thinking that calibration of these cold stores might not be necessary if I have a master IR thermometer to calibrate them. Meaning to say, the temperature displayed on the IR should match the temperature displayed on the temperature LED panel. If there's a vast difference between the two, it would then be appropriate to get the coldroom calibrated. 

 

Also, this may potentially be a silly question, but can maintenance/servicing = calibration, with regards to cold room/cold storage? 

 

Cheers, 

Clover

To be honest we always have done it weekly, since well before I started working here. We do love a bit of calibration here as our scales are done daily. Not a huge issue as it only takes 5 minutes but I don't think it's totally necessary. We sent the gun back to the manufacturer twice for replacement and when the 3rd one was no good we just told them to stuff it. We calibrate our coldrooms with data recording discs that automatically measure the temperature for 7 days and match their readings against those of our probe thermometer every week when we change them.

 

To be honest I'm not sure about whether servicing=calibration as the contractor we have at our place doesn't ever test his work. He just fixes what he deems to be the problem and leaces it to us to make sure we're happy he's got it right.

 

Hope some of this helps,

 

Andy

[Charles.C]

Hi Andy, 

 

I see. Yah, I guess you could punch a hole into the ice if it's thin enough. Weekly calibration seems kinda excessive? Why did you decide to do it weekly? 

 

Good to know that there are people with the same problem! What a relief. So, did you throw the faulty one away or get it repaired? 

 

On a different note, how often do you calibrate your walk-in chillers, walk-in freezers, chiller/freezer trucks? I'm thinking that calibration of these cold stores might not be necessary if I have a master IR thermometer to calibrate them. Meaning to say, the temperature displayed on the IR should match the temperature displayed on the temperature LED panel. If there's a vast difference between the two, it would then be appropriate to get the coldroom calibrated. 

 

Also, this may potentially be a silly question, but can maintenance/servicing = calibration, with regards to cold room/cold storage? 

 

Cheers, 

Clover

 

Hi Clover,

 

I have never heard of an IR thermometer being used in a standard for routinely monitoring/accepting-rejecting the temperatures of chilled/frozen storages or freezing units.

 

IMO, if you think about the FS objective, the reason is self-evident.

 

But if you can provide a validated example, i am only too willing to be astonished.

[clover]

Hi Clover,

 

I have never heard of an IR thermometer being used in a standard for routinely monitoring/accepting-rejecting the temperatures of chilled/frozen storages or freezing units.

 

IMO, if you think about the FS objective, the reason is self-evident.

 

But if you can provide a validated example, i am only too willing to be astonished.

Hi Charles, 

 

we are using IR thermometers to take temperature of cold storage. I fail to see anything wrong. As long as the IR is calibrated. What kind of validated example do you mean? Our procedure is quite straight forward. Simply aim and shoot the IR thermometer at the walls of cold storage, hold for 5 seconds and take recorded surface temperature. Same goes for ingredients. Not so much for frozen, as if it comes in solid hard, needless to say it's safe. But more for chilled ingredients. 

[* Steve]

Firstly, if you are carrying out checks with weights internally to check accuracy, it is termed 'verification' rather than calibration. Calibration is usually carried out by an external source and involves checking AND modifying of the settings if not sufficiently accurate. With regards to weights checking range this is more to do with the range that YOU use the scale rather than the maximum range of the scale. i.e. if you have a 30 KG scale but only ever use it for weighing from say 10 Kg to 20 Kg, then you would check it in the range of between 10 Kg to 20 Kg. 

[Charles.C]

Hi Charles, 

 

we are using IR thermometers to take temperature of cold storage. I fail to see anything wrong. As long as the IR is calibrated. What kind of validated example do you mean? Our procedure is quite straight forward. Simply aim and shoot the IR thermometer at the walls of cold storage, hold for 5 seconds and take recorded surface temperature. Same goes for ingredients. Not so much for frozen, as if it comes in solid hard, needless to say it's safe. But more for chilled ingredients. 

 

Hi Clover,

 

Little bit OT

 

It's probably easier to discuss with raw data.

 

IMEX storage conditions are typically qualified/compared via air temperature.

Can you post some IR sampling data to validate a correlation between wall temperature and air temperature of chilled/deepfreeze storage.

 

IMEX stored, packed ingredients are typically qualified by ingredient core temperature (CT).

Can you post some IR sampling data to validate a correlation between CT of packed product and the outside of packing temperature.