Calibration Method for Scales and Flowmeters

#1
Hi,

I recently joined my employer - previously there was no internal calibration and only last year was there an external calibration.

Would using a standard repeatability calibration method be suitable for scales? And can anyone recommend for flowmeters? Any suitable calibration method I can use for in-house calibration on the scales and flowmeters?

I would appreciate it.
 
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Jen Kirley

Quality and Auditing Expert
Leader
Admin
#2
Welcome Nashi!

The answer is, as always a maddening "It depends."

Calibration programmes are mostly based on criticality of measurements, instrumentation and the environment the tools are used in.

Start with critical features, and the instruments that measure to what tolerances. Expect your tools to be capable of reading in finer discrimination than the measurement. In industry that is usually the "10:1 rule" simply because the decimal point is easy to manage in discrimination management. That said, I have yet to see a firm requirement for 10:1. Some cases of 4:1 also suffice.

The instruments themselves are considered, as some are delicate while others are very durable. Calibration method and frequency is determined in part by this as well as the environment and controlled manner they are stored in. Most of my clients have heir scales checked monthly or less often, but I had a client whose scales were professionally calibrated weekly because their processing areas were industrial, which meant an appreciable risk of the scales getting bumped, and their product was bagged pure silver flake.

Lastly, we have frequency of use, environment of use and the tolerance the tools are expected to measure. I am thinking of tools like calipers in a machine shop. Schedule their calibration checks based on the wear and tear they endure, the accuracy they are expected to oversee, and the cost of getting it wrong.

I hope this helps.
 
Last edited:
#3
Welcome Nashi!

The answer is, as always a maddening "It depends."

Calibration programmes are mostly based on criticality of measurements, instrumentation and the environment the tools are used in.

Start with critical features, and the instruments that measure to what tolerances. Expect your tools to be capable of reading in finer discrimination than the measurement. In industry that is usually the "10:1 rule" simply because the decimal point is easy to manage in discrimination management. That said, I have yet to see a firm requirement for 10:1. Some cases of 4:1 also suffice.

The instruments themselves are considered, as some are delicate while others are very durable. Calibration method and frequency is determined in part by this as well as the environment and controlled manner they are stored in. Most of my clients have heir scales checked monthly or less often, but I had a client whose scales were professionally calibrated weekly because their processing areas were industrial, which meant an appreciable risk of the scales getting bumped, and their product was bagged pure silver flake.

Lastly, we have frequency of use, environment of use and the tolerance the tools are expected to measure. I am thinking of tools like calipers in a machine shop. Schedule their calibration checks based on the wear and tear they endure, the accuracy they are expected to oversee, and the cost of getting it wrong.

I hope this helps.
Welcome Nashi!

The answer is, as always a maddening "It depends."

Calibration programmes are mostly based on criticality of measurements, instrumentation and the environment the tools are used in.

Start with critical features, and the instruments that measure to what tolerances. Expect your tools to be capable of reading in finer discrimination than the measurement. In industry that is usually the "10:1 rule" simply because the decimal point is easy to manage in discrimination management. That said, I have yet to see a firm requirement for 10:1. Some cases of 4:1 also suffice.

The instruments themselves are considered, as some are delicate while others are very durable. Calibration method and frequency is determined in part by this as well as the environment and controlled manner they are stored in. Most of my clients have heir scales checked monthly or less often, but I had a client whose scales were professionally calibrated weekly because their processing areas were industrial, which meant an appreciable risk of the scales getting bumped, and their product was bagged pure silver flake.

Lastly, we have frequency of use, environment of use and the tolerance the tools are expected to measure. I am thinking of tools like calipers in a machine shop. Schedule their calibration checks based on the wear and tear they endure, the accuracy they are expected to oversee, and the cost of getting it wrong.

I hope this helps.
Thank you Jen.
 

ChrisM

Quite Involved in Discussions
#4
Scales: Do you have a requirement for traceability to National Standards? If so, you will have to arrange this (ideally get a company to visit your site and calibrate the scales at their point of use; they should not be moved since movement can affect accuracy).
If no such requirement, write your own procedure. Obtain a suitable set of weights that cover the range of your various sets of scales, each scales should have at least three values. Get these weights calibrated or buy them with calibration. Check each set of scales with at least three weights, with each weight placed in ideally 5 places (each corner and the centre, adapt if the plates are round); state your accuracy requirements in the procedure, and in general, job done. Make sure date and name of calibration technician are recorded and that the calibration technician is suitably trained etc.

Calibration intervals are up to you to set depending on usage, accuracy requirements etc. Your set of calibrated weights - if they are properly looked after and stored suitably, they won't alter their weight so you could give them a calibration interval of, say, 5 years or more. It all depends on your industry/customer requirements, what standards you are operating to, etc
 

dwperron

Trusted Information Resource
#5
A lot is going to depend on the mix of instruments you have. Are all the scales about the same capacity? In that case, getting the calibrated weights you need and doing them in house makes sense. If you have a couple of everything from platform scales to microbalances you are probably better off getting someone who already has the standards.

Flowmeters, are they gas or liquid? That makes a huge difference. If you have a lot of them that are not very accurate (2 to 10%) it might make sense to purchase the equipment to calibrate these in house. Only a few of them? Leave it to an outside lab.
 

Mike S.

Happy to be Alive
Trusted Information Resource
#6
For scales (and a lot of other T&M equipment) I like long calibration intervals (like a year or two) but frequent internal verification.
 

QChas

Involved - Posts
#7
Scales: Do you have a requirement for traceability to National Standards? If so, you will have to arrange this (ideally get a company to visit your site and calibrate the scales at their point of use; they should not be moved since movement can affect accuracy).
If no such requirement, write your own procedure. Obtain a suitable set of weights that cover the range of your various sets of scales, each scales should have at least three values. Get these weights calibrated or buy them with calibration. Check each set of scales with at least three weights, with each weight placed in ideally 5 places (each corner and the centre, adapt if the plates are round); state your accuracy requirements in the procedure, and in general, job done. Make sure date and name of calibration technician are recorded and that the calibration technician is suitably trained etc.

Calibration intervals are up to you to set depending on usage, accuracy requirements etc. Your set of calibrated weights - if they are properly looked after and stored suitably, they won't alter their weight so you could give them a calibration interval of, say, 5 years or more. It all depends on your industry/customer requirements, what standards you are operating to, etc
Exactly how we do it. Weights are calibrated every 3 years (outside with certs). We do our scales internally every 6 months
 

BradM

Leader
Admin
#8
For flow meter, is it for like water flow? You might could use a stopwatch, accurate scale and test the weight over time.

For scales, it depends on risk, how often it is used, and what the impact would be without a calibration.

It seems a bit to me to be kind of fruitless to argue the stance "I want to save money. Must I calibrate?" You should first focus on if those instruments are important. If they are, then come kind of calibration/verification is in order.
 
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