Thursday, 6 August 2015

Is 99.9% was good enough...

Achieving 99.9% accuracy in anything would seem to be pretty impressive. 

But according to some research done a while ago, it may not be good enough.

Apparently, 99.9% accuracy would mean that the US Postal Service would mis-handle 18,322 items per hour. Doctors would write 20,000 incorrect drug prescriptions per year. Manufacturers would produce 5.5 million cases of fizzy drinks that were flat. And two planes per day landing at Chicago O’Hare airport would be unsafe.

These statistics and more are freely available on line. Just Google “If 99.9% was good enough” to check yourself.

Accuracy then is key but just how accurate is your axle weighing system?

Weighing a heavy goods vehicle on a system that is accurate to 2% might sound impressive. But 2% of what?  Two systems which claim to weigh to within 2% can actually have wildly different accuracy.

For a percentage to be meaningful, you have to know what 100% is. But the weighing machine doesn’t know what 100% of the axle weight is. If it did, why not display it?
An axle Weighbridge - but how accurate it it?

So what does the 2% refer to?

When scale manufacturers refer to accuracy as a percentage, they mean a percentage of the capacity of the weighing machine.

If a machine has a capacity of 30,000kg with an accuracy of 2%, it means it will weigh to within 600kg.

If a machine has an accuracy of 2% but a capacity of 15,000kg then it will weigh to within 300kg.

Both machines have the same accuracy statement but the lower capacity machine will offer twice the accuracy

And weighing your vehicle on a system that was only accurate to within 600kg would leave it very vulnerable to a prosecution for overloading.

We strive for the greatest accuracy we can when designing a system. Our dynamic axle weighbridge for instance can achieve an accuracy of 0.25%. With a capacity of 20,000kg, more than enough to weigh the heaviest vehicle on the road, that means an axle will be weighed to within 50kg.

Some manufacturers like to muddy the waters by quoting OIML Class numbers or even not quoting an accuracy figure at all.

So how accurate is your axle weighing system? If you think we can help check for you then we’d be happy to do so.

It might prove to be an eye opening exercise.

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