Scale calibration is normally carried out with the belt running under different loadings which are applied from a test chain supported by the belt over the scale length. Scale manufacturers can calibrate the belt for you & it should only be necessary to have the operation witnessed by TUV, Lloyds etc. If you have the good old ISO 9000 certificate business the manual must be able to direct you to the particular authority. It will probably be your ISO Assessor, or their preferred in-house facility. But for economy you should ask the scale manufacturer to do the actual work. A laboratory will only rent the chain from the manufacturer anyway & then charge you an arm & a leg for learning how to use it. ■

Chains and test weights are not ideal when trying to calibrate a belt weigher as they don't exactly emulate the dynamic conditions of material travelling up the belt. The only really acceptable way of calibration which can be traceable is to use Material checks. Run either a known amount of material over the weigher or catch the material and post weigh it.

If you would like a "do's and don'ts of belt weighers" please let me know.

Jon Scarrott

www.lodestone-electronics.com ■

Post weighing is a control integration operation. There is no more chance of synchronising the print out to the load fluctuations from just a given accumulated mass than there is by loading the chain with a known burden.

If the installation exists, as it seems to, then chutework must be removed & means provided to collect a whole lot of lignite & water. If there is an inclined section before the collection point then the water will not be weighed accurately, if at all. So you have to make sure the chainless test is carried out in sympathetic weather, or indoors where the chute removal operations might be constrained. ■

Hello to the Greek Lignite industry. I visited all the Greek power stations last year and looked at all your belt weighers.

Under EU rules, the only way you will get a legal or certified test is if you (1)Use a MID approved instrument and (2)Test the equipment in accordance with OIMLR50.

This will mean running 5 pairs of live load tests and the accuracy of each test load will have to be 3 x better than the accuracy you are trying to test the belt weighers to.

You can test your weighers as Class 0.5, Class 1.0 or Class 2.0 systems.

Its a hard road to achieve properly certified belt weighers. It requires some planning. You will need a reliable test circuit and a good static bin or weigh bridge to act as the 'control instrument' which is used to establish the true weight of each test load. ■