8 replies to this topic

[mckief]

Hello,

I am looking to review my companies calibration procedures and the way we currently calibrate our scales. The site does not sell any products by weight. But has scales it uses throughout the facory for various tasks.

I therefore wondered if anyone can provide clarification as to if the scales can be calibrated in house with stamped weights that are sent away annualy for calibration or if they have to be calibrated by an external company that comes in and calibrates all scales on an annual basis .

[George @ Safefood 360°]

Hi mckief,



I'm going to use the BRC standard as reference to address your question. It states that the company shall identify all equipment used for CCP monitoring or the safety and legality of the product. So, your job of work is

· make acomplete list of all measuring items in the plant

· risk assess each of these and decide if they are used for CCP monitoring or are required to produce safe and legal products. (In other words if the item was togo out of calibration could this lead to the production of unsafe and illegal food products - I'm sure you get the picture)

· for those that are, you need to define the frequency of checking and adjustment and in all cases they must be traceable to a recognised standard. There is no hard and fast rule about how this is done. But whatever you do you must be confidentthat if a high risk item (used for CCP's, for example) drifts out of calibration for whatever reason, your system can detect this in a timely way and protect the health of your customers.

· Document the above.

For CCP's you can use internal reference standards which are calibrated and traceable to are recognized standard or you can use an external calibration body in all cases or a mixture of both. It really depends on your assessment of risk, nature of the inspection item, condition of the item, conditions of use, etc. You need to make this call based on your experience and knowledge of the process andequipment.


Consult with the calibration body, suppliers of the equipment or your peers in similar food processing operations for guidance. In regard to the scales that are not used for CCP's, safety or legal checking. I would suggest that internal standard masses certified to a recognised standard can be used for internal checking. These of course should be certified at a predefined frequency. In short it is my opinion that the answer to your last question is Yes.

[Charles.C]

Dear mckief,

I echo George's response and particularly his caveats in that it may very well depend on what you are doing, where and what for, and any local legislatory requirements.

George mentioned the use of frequencies to refer yr suggested in-house calibration procedure. In relation to another thread on this forum, I previously sought to answer a similar query. I found any offical and even semi-official solutions elusive, other than highly mathematical formulae based on yr own existing risk assessment data (which most people will not possess of course.)It seemed to me that most people were simply quoting published documents, often from equipment manufacturers, which contained "suggested" starting frequencies. I posted the links / documents for these in the thread, but basically the numbers appeared quite arbitrary (typically 3months to 1year) except that where, for example, it was obvious that items in use were losing their calibration in a short time, very frequent checking was the norm., eg IMEX spring balances in a wet environment must be individually checked every day before use against a sub-master checkweight. I guess you can call that a risk assessment.

@George - would certainly be interested if you hv any links to "official" calibration frequency sources as I basically failed to locate any (usable) compilations.

Rgds / Charles.C

[mind over matter]

Hello,

I am looking to review my companies calibration procedures and the way we currently calibrate our scales. The site does not sell any products by weight. But has scales it uses throughout the facory for various tasks.

I therefore wondered if anyone can provide clarification as to if the scales can be calibrated in house with stamped weights that are sent away annualy for calibration or if they have to be calibrated by an external company that comes in and calibrates all scales on an annual basis .

You might also check the following link for the recommended practices.

http://www.ncsli.org/

(Disclaimer: I'm not connected to the NCSL International in any way.)

Edited by mind over matter, 14 January 2012 - 08:37 AM.

[Charles.C]

You might also check the following link for the recommended practices.

http://www.ncsli.org/

(Disclaimer: I'm not connected to the NCSL International in any way.)

Dear MOM,

Interesting organisation / procedures but i think you have to be a member. And "donate".

Rgds / Charles.C

[George @ Safefood 360°]

Dear mckief,

I echo George's response and particularly his caveats in that it may very well depend on what you are doing, where and what for, and any local legislatory requirements.

George mentioned the use of frequencies to refer yr suggested in-house calibration procedure. In relation to another thread on this forum, I previously sought to answer a similar query. I found any offical and even semi-official solutions elusive, other than highly mathematical formulae based on yr own existing risk assessment data (which most people will not possess of course.)It seemed to me that most people were simply quoting published documents, often from equipment manufacturers, which contained "suggested" starting frequencies. I posted the links / documents for these in the thread, but basically the numbers appeared quite arbitrary (typically 3months to 1year) except that where, for example, it was obvious that items in use were losing their calibration in a short time, very frequent checking was the norm., eg IMEX spring balances in a wet environment must be individually checked every day before use against a sub-master checkweight. I guess you can call that a risk assessment.

@George - would certainly be interested if you hv any links to "official" calibration frequency sources as I basically failed to locate any (usable) compilations.

Rgds / Charles.C

Hi Charles

Check out BS 5781:Parts 1 and 2 Measurement and calibration systems. Specification for system requirements.

I used this standard many, many years ago while responsible for a injection moulding operation making food packaging. I found it very good and is ideal for drilling down into the finer detail, statistical bases of calibration systems. These standards seem to find a welcome home in true engineering operations but not so much in the food sector. I can't say why this should be the case. I'm sure these standards have been superseded by more recent ones, but they are just the ones on my shelf at the moment. The BSi also produce specific standards for the calibration of certain instruments like torque meters (for those in the bottling sectors). Also check out ISO standards for calibration. They will apply to laboratories etc but the principles and standards are relevant.

In general the development and use of standards for calibration frequency would be an act of folly since the accuracy, precision and drift of even two identical instruments can vary. You can perform some simple plotting of data on a specific item of measurement equipment to determine its capability against calibration tolerances and the rate of drift etc and this will give you the real picture. It will require a little work, of course, but would be valuable in validating you calibration plan.

I tend to operate a simple rule - if it's a CCP it should be checked daily (if possible) against an internal certified standard and work back from there.

I suppose at a plant level in the food industry there is a limit to what we can expect from food technologist when it comes to statistically valid calibrations plans. Especially since it is not covered in the content of food technology programmes.
George

[mckief]

Thank you for your help. It was very useful.

[Charles.C]

Dear George,

Check out BS 5781:Parts 1 and 2 Measurement and calibration systems. Specification for system requirements.

Thanks, looks interesting. I'll try and locate next time I'm in a technical library.

I agree yr comments about the difficulty in defining an "average" balance as a reference but IMEX this is what practical engineering is all about. Even in this PC age, nomograms / rules-of-thumb are still the name of the game perhaps! .

Rgds / Charles.C

added - @mckief, you might find this thread on calibration intervals interesting, contains discussion and a variety of attachments although I must admit fails to provide an explicit answer to yr query.

http://www.ifsqn.com...dpost__p__32675

I noticed 2-3 mentions (and summary) of interval methods using a BS standard which i believe is an updated version of the one given by George previously. Sadly no actual numerical example/extract given for the interval procedure described.

Somewhere in the forum there is, I think, another suggested table of starting intervals for balances although as already stated, the conditions, criticality of data, etc will challenge any average number system.

From the simplicity (to me anyway) of some of the statistical formulae presented, one can see the need for short-cut solutions / presentations.

[omuntu]

What we do in my factory is that we get the standard weights calibrated, then we calibrate the weighscales monthly using the standard weights.