CALIBRATING WEIGHING MACHINES
Calibration weights, calibration instructions

 

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Summary of this article as a two-page .pdf download

SUMMARY

Every balance will go out of calibration given enough time, or if bumped or dropped. The readings become inaccurate. It is possible that it will be 'broken' but it is much more likely that it merely needs calibrating.

Or you could look at it this way: one day your balance will "break down", but the chances are that you can fix it simply by pressing buttons.

You will need an accurate weight. We strongly recommend you buy the weight when you buy the balance.

You will also need to the instruction that was supplied with the balance (the calibration instructions vary from model to model).

IF THE BALANCE IS NEW IT WILL STILL BE FACTORY-CALIBRATED, LEAVE IT ALONE!

IF IT IS READING CORRECTLY, LEAVE IT ALONE!

IF IT AINT BROKE, DON'T FIX IT!

 

WHAT IS 'CALIBRATION' ?

The reading on a measuring device (any measuring device, e.g. a thermometer, weighing machine, clock...anything) must match the units it is measuring (e.g. degrees, grams, minutes). This matching-up is called calibration. Electronic machines go out of calibration, it is the nature of electronics.

When a balance goes out of calibration the readings will not match the units, e.g. a 100g weight might weigh 105g.

Every scale will go out of calibration given enough time or if bumped or dropped. In the scientific industry scales have the calibration checked every year. That is why every scale in a laboratory or hospital has a sticky tab with the date it was last checked. A technician will call, he will check all the scales in the building, he will calibrate any that are not accurate, he will charge a minimum of £100.00 for the visit. If you have a low-value scale it is cheaper to calibrate it yourself. Buy a weight and follow the instructions in the instruction leaflet.

 

HOW DO YOU KNOW IF IT NEEDS CALIBRATING?

Weigh a weight, if it is reading correctly, the scale if fine, there is no need to calibrate it, just leave it alone.

If the balance is not reading correctly, it will probably need calibrating.

If the display is slowly 'drifting' up and down, even when nothing is being weighed, this means that someone has seriously overloaded the balance, it is beyond repair.

To recalibrate it yourself, you will need an accurate weight. These are not not usually* included with the balance, but they are not expensive, I'd recommend buying one when you buy the balance, to save on postage costs. Please keep the instruction leaflet in a safe place, we do not have copies of the calibration instructions for discontinued models. * some balances that weight down to 0.001 have a weight included.

 

D.I.Y CALIBRATION

Calibrating it yourself involves pressing buttons (sometimes in a complicated sequence) and placing a weight on the weighing platform.

Which buttons do you press?
It varies from model to model. See the instruction manual.

Which weight will you need?
It's usually the maximum weight the scale will read (e.g. 500g for a scale with a capacity of 500g). Some scales require two weights. Annoyingly, the instruction manuals don't tell you which weight you need, they just say, "place the required weight on the weighing platform". The good news is: the weight required for each machine is listed in each item description on the QUICKTEST website.

I do strongly recommend that you buy a weight but if you really don't want to spend money you can check it using coins: 5p=3.25g, 1p=3.56g, 10p=6.5g, 2p=7.12g, 20p=5g, 50p=8g, £1=9.5g, £2=12g. For instance, one £2 coin + four £1 coins = 50g (If you want to know the weights of old coins, including gold and silver coins throughout the world, see The Gold & Silver Buyers Handbook). Don't use coins for balances that read down to 0.01g or 0.001g, the coins will be too light due to wear.

Do not try to calibrate a balance without the weight, you will merely reprogram its electronics and then have to buy a weight to calibrated it properly.

 

HOW OFTEN SHOULD A BALANCE NEED CALIBRATING?

How often you have to calibrate a balance depends on the quality of the balance.

Very approximately, this is how often you should calibrate it, and this applies to any scale bought from anyone, irrespective of what the seller claims!

- if you paid a few hundred pounds, every year or two
(calibration guaranteed for one year - if you can't calibrate it, we'll do it for you, for free)

- if you paid about £100.00, after about a year.
(calibration guaranteed for one year - if you can't calibrate it, we'll do it for you, for free)

- if you paid about £50.00, every few months
(calibration guaranteed for six months - if you can't calibrate it, we'll do it for you, for free)

- if you paid about £20.00, every few weeks
(calibration guaranteed for three months - if you can't calibrate it, we'll do it for you, for free)

- if you paid about £10.00 there really is no guarantee that it will stay in calibration from one week to the next, this is not a fault, you get what you pay for.
(calibration guaranteed for one month - if you can't calibrate it, we'll do it for you, for free)

After these times, we can still calibrate it for you (if you can't do it yourself) but there will be a charge of £5.00 + £6.50 UK postage.

There is no harm in calibrating it every few months, weeks or days, but it is not necessary unless it has become inaccurate. It is more important to check it regularly (by weighing a weight) to see if it needs calibrating.

 

SPECIAL RULES FOR APPROVED BALANCES

Balances that are approved (by Trading Standards) for use in trade (buying by weight) are calibrated in one of two ways.

The approved balances by A&D are calibrated for use at one location (when Trading Standards calibrate them, they allow for variations in gravity, read all about it). If it goes out of calibration or if you want to use it at another location, it must be calibrated again (by Trading Standards) which costs about £100.00.

The approved balances by Ohaus can be used anywhere, they do not need to be calibrated to a location. You CAN calibrate these if they become inaccurate, there is a weight inside the scale and you check it by pulling little lever (low-tech, that's why these scales are not expensive).

See all models (new).

We usually have some that are secondhand and clearance.

 

RELATED ARTICLES:

Everything you would ever want to know about weighing and weighing machines

Approved balances


Basic instructions for calibration .pdf leaflet (download)


RELATED PRODUCTS:

Approved balances for use in trade.

Small balances that weigh down to 1g or 0.1g or 0.01g or 0.001g

Larger balances (bench scales), battery-operated or mains-powered

Mechanical balances (spring balances)

 

QUICKTEST, Watford, WD18 8PH, Tel. 01923 220206, email info(at)quicktest.co.uk