Friday, 27 September 2013

These things aren't accurate, mate!

A topic that comes up time and time again is the subject of accuracy. If I had a £1 for every time someone has approached me a comment along the lines of, ‘my brother has a mate who met a bloke down the pub who says these things aren’t accurate” I’d be very rich now.


But the truth about weighbridge accuracy is somewhat different.

It’s not unusual to find a variation between weighbridges; if one weighbridge is working at +20kg and another is working at -20kg, that’s a 40kg difference and yet both could be weighing within specification.
The dynamic axle weighbridges we produce can be installed to an accuracy of 0.25%, good enough to allow them to be offered as a Public Weighbridge and the best accuracy in the world from an axle weighbridge.

What many people don’t realise is that after initial calibration, there is no legal requirement to have any weighbridge calibrated ever again unless there is a major fault. In reality it’s just simple good practice to have your weighbridge calibrated regularly; once every two years ought to be enough.
Public weighbridges will often be tested by Trading Standards without notice but many go some considerable time between tests.

I know we have a few customers who won’t spend the money on a calibration and as long as the display keep showing numbers, they’re happy and assuming the weights are right. If they are then there’s no problem but if they’re not then someone is going to notice and spread the word about ‘these things not being accurate’.
Dynamic axle weighbridge being dead weight tested.
Axle Weigher under test using our unique calibration vehicle

The VOSA network of enforcement axle weighbridges aren’t treated the same way. We have to test them rigorously every six months including checking that the concrete approach levels are still within tolerance. A VOSA weighbridge cannot be used for prosecution if its calibration certificate has expired and each calibration certificate lasts a maximum of six months. So if you are weighed on a VOSA dynamic axle weighbridge you can be sure it has been well maintained, regularly calibrated and highly accurate.

Even so, the weighbridges are operated with a tolerance allowing hauliers some leeway.

That’s not to say you’re allowed to run above the legal axle limit. Even small overloads if they are consistently found will be prosecuted but the tolerance allows a margin for error in the event of an inadvertent overload.

Incidentally, we operate the only weighbridge test vehicle purpose designed for calibrating axle weighbridges. And as well as calibrating the VOSA network we use it for installing every single system we install and can hire it out to anyone who needs to check their axle weigher.


Accuracy is basically all down to good practice and routine maintenance. You’d do it with your trucks so why not the weighbridge?

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