Calibration Made Simple

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Russ Edwards

Published on 24 March 2021

Ok, so if you’re here it’s likely you’re in an industry or field that already has an idea of what calibration is. Maybe it’s your job to arrange it, or perhaps the place you work at don’t do it and you know deep down that you really should (we won’t tell anyone if you don’t). It’s actually more common than you think! By the end of this article, you’ll know what calibration equipment is, when you need to do it and why you’re doing it in the first place.

Do I Need Calibration?

Long story short…yes.

“I’ll just buy a new one when the time comes.”

Have you ever said that? Perhaps a colleague or manager? Or maybe just your own Peep Show style inner monologue?

The trouble is, ‘just’ buying a new one won’t fix the problem – it literally creates a brand new shiny one. The point of calibration is to make sure your equipment is doing exactly what it should – when it should. Buying new doesn’t guarantee this, especially if it’s been shipped from Outer Mongolia because it was £3.68 cheaper and gave you free delivery.

It can’t be promised everyone treated your new prized purchase with a gentle touch, so it’s likely it took some knocks along the way – and if it’s not properly packaged, a little tap can make an instrument read completely off. That’s a bit annoying when you waited 34 days for it to arrive on a slowboat in the first place.

No, putting equipment through its paces – old or new – is the only way to prove it’s working properly.

Take Ikea; you’ve seen those robotic contraptions in the glass boxes dotted about showing the mattress can be ‘jumped’ on (say no more), or the kitchen drawers being opened and slammed shut a zillion times a day – one assumes in real life this would be by an over-zealous and likely hangry toddler. They’re tested to the maximum so they can ensure they will keep working better, for longer.

How Is Calibration Done?

When calibrating equipment, a qualified engineer takes your instrument and puts it through its full capabilities, or ‘range’ if you will. That means the very bottom and very top of where it is able to read. It definitely, categorically and absolutely must read accurately through its entire scale…not just where you use it most. Otherwise, how do you know it’s correct where only you need it to be?

Every individual item has a ‘permissible tolerance’, usually set by a National Standard or an internal QA department, and this is a small percentage of error that is allowed in the eyes of the manufacturer for it to be considered a-ok for service.

Listen. We’re not naming any names here – snitches get stitches – but we have over the years comes across ‘calibration houses’ (business that perform calibration) that don’t do things properly. For speed, they test it at the median (middle) point and assume it’s working in a similar way across the board. We all know what happens when we assume. Worse, they may even simply give it a little look over, throw a sticker on it and call it jobs a good ‘un. It’s quite scary when that happens but at least when you realise, you know you’ll be making sure it isn’t happening again.

How Do I Know My Calibration Is Done Right?

One warning sign is if said sticker doesn’t have anything unique about it, maybe just a logo and a phone number.

There should be a unique reference number (URN) for a kick-off – this is usually the number allocated and likely stamped on somewhere by the manufacturer, but in the circumstance that it wasn’t given one, the calibration house might dedicate one of their own job numbers to it. As long as that number has never been used before, it’ll help you trace its instrumenty roots.

As well as a URN, there should be two dates – one when it was tested, and one when its due to be tested again. That may seem like overkill, but depending how often the item is used really determines how often you should get it checked out; 3 months, 6 months, annually etc. That way there is no question about whether it’s due up or not.

It’s super handy if the contact details are on there already too, just in case, as it makes it all the easier to do a bit of instrument-digging.

So. They’ve been, they’ve gone. They’ve left an empty coffee mug on your desk without using the coaster. Hmm the sticker things seems to check out. But you’re still left wondering…what did they test? What equipment did they use to test it? Will they send me any paperwork? How do you get water marks out of teak? (Lemon juice and salt buffed out with a soft cloth, by the way.)

When done correctly, every item tested will have ‘traceability’, which as the name suggests, is the ability to er…trace something. It will take you on a journey right back to when it was made and by whom, up to its latest calibration record (or from cradle to grave if it’s no longer in service). This means that if, God forbid, anything was to go wrong, the traceability (and supporting calibration certificates) would rule out that the issue stemmed from your equipment.

Less drastically, if you had a question about an instrument’s history, giving that serial number to the company would make you come over all Zoltar – you’d know everything you needed to sooner than you could play ‘Chopsticks’ on an oversized floor-piano.

Not only would it tell you about YOUR instrument, but also what instrument was used to test it, which will in turn have its own traceability and so on…can you see why it’s so important now?

It may seem like it’s no biggy, but in certain places, such as hospitals, this is even more crucial. Who wants to glance over at some equipment they’re hooked up to and see that it hasn’t been tested for over 2 years?

Regardless, if your equipment performs a job, think about this; what does it perform a job on? And what does that perform a job on…? And what does THAT perform a…ok, I’m sure you get it now. Suddenly there’s a bigger picture and responsibility to consider. Gulp.

Calibration Equipment

To go into every conceivable calibration process for every conceivable instrument would be nigh-on impossible – a set of precision weighing scales wouldn’t be tested in the same way as a sphygmomanometer, a digital vernier, or a high-level tank alarm for example. Some processes can take hours or use huge equipment that can’t be moved.

However, at the very least, any calibration procedure will involve hooking the equipment up to a piece of Master Test Equipment (which is tested by an external source) to check the readings at its lowest, highest, and a range of mid points, to ensure its consistent in what it’s telling you. These are then checked against the permitted tolerances we mentioned earlier, and its results are recorded ready for your calibration certificate.

The calibration house will have its own strict Quality Assurance methods which are externally audited, meaning that they have procedures that they must follow to the letter.
Finally (for the engineer at least), it’ll be given a thorough inspection and check for anything damaged or needing further attention, and a clean-up if necessary, before being reinstalled on site or packaged up for safe shipping back to the customer. The certificate is then lovingly typed up, checked thoroughly, and sent over to you with the goods.

If, however, your equipment fails, the technician can repair it if feasible to do so, or quote for a replacement – don’t forget to get a new calibration certificate for that one too.

Summary

• Calibration is testing something thoroughly to check it is working through all of its range
• It’s done periodically depending on how often its used and in what setting
• You’ll get a certificate telling you how it performed and if it passed or failed
• If you need it, there’s full traceability to track its full calibration history
• If it needs repairing, the engineer will do so and recalibrate it
• You’ll need it for your own Quality Assurance Audits

If you find yourself needing calibration whether it is on-site or in house, here at GNW we can support your needs, simply call one of our friendly experts on 01704 536010 or email us at sales@gnw.co.uk and we will get back to you.