Dear YVRpilot,

Looking at your profile, I see that you are involved in wood chippings. If that is the product you wish to measure with a belt weigher then I would propose that it is a very difficult task to achieve +/- 0.25% with long term repeatabilty.

With a bulk density of around 0.2 t/cum and I would suspect a lowish throughput due to bulk constraints. You will need to specify all of these parameters in order to get a reasonable assessment as follows:

Conveyor type

coveyor shape (ie straight or catenary)

Idler type

belt width

belt thickness and type

troughing angle

belt speed

belt length

conveyor incline angle

throughput in t/hr

belt tensioner type

motor size

weighbridge availablity for load tests

Minimum and Maximum throughput

Regards

Jon Scarrott ■

To YVR Pilot,

1) - I imagine you would need a multi-idler scale with at least 4-6 idlers to achieve repeatable and reliable 0.25% accuracy.

2) - If it is essential to have that accuracy, you may want to take a slightly unconventional approach and consider a second scale, each of which would provide a check on the other. At least if you got significantly different readings, you would know immediately and could recalibrate both scales.

3) - When you are loading large ships at a high fill rate, the $25,000 cost of a second check scale is not so high in comparison to being out by a few hundred tons of product.

4) - I believe that the Milltronics belt scale is one of the best conventional belt scales. T.W.Mackay is the distributor in Vancouver; have you contacted them?

5) - The true weight of pellets also requires an accurate measurement of moisture content; so you might want to check out Acrowood's Drywood moisture measurement system, which includes an accurate weigh scale.

Paul Janze

Sandwell Engineering Inc.

Vancouver, BC

tel: 604-638-4628

email: pjanze@sandwell.com ■

YVR pilot,

We have been installing belt scales since 1980 with the last 10 years focused on precision scales which are installed at most ports in Vancouver. Many are certified, one of which is Canada's 1st 0.1% approved belt scale.

Our approach is sound engineering which takes into consideration conveyor dynamics.

We are quite innovative and incorporate several factors other scale mfg have not considered.

We also have monitored and compared draft/rail scale/conveyor scale reading for several years now and are very confident in our belt scale solutions.

Our business comes mostly from referrals and usually after someone else failed to deliver required accuracy.

Lorne Danielson,

TD Micronic Inc.

604 594-9191 ■

YVR pilot,

A simple question:

how do you assess that the system is weighing to 0.25%?

Probably not with a site lorry weighbridge which are nominally 0.5%. I think you would probably require an in-line static weighing system to catch and measure batches of material. This could then measure to the order of 0.1%. An expensive option, but if the measurement is important then maybe worth the money.

I don't think it's possible to come anywhere close to 0.25% for an extended period of say 3 months. The closest I ever came to a weighing system with a consistent weighing accuracy of 0.5% for a period of 6 months, was an Inflo system. The weigh carriage was a true force collection system and the transducer was a vibratiing wire type.

I you are persuaded that a company can provide a 0.25% system then ensure that you include a tight contractural condition about performance and time span. Most sensible weighing companies will walk away.

Jon Scarrott ■

I agree that 0.25% is rarely achieved over longer term.

In general 'brochure accuracy' is for components supplied and does not include a many errors attributable to the belt/conveyor system

.....ie all belt scale are great until you install them onto a conveyor.

We have component accuracies in the order of 0.05% to 0.01% and installed system accuracies of 0.25% or better.

Not every conveyor is suitable for high accuracy belt scales.

However we have several certified tests (with reference of 0.01 - 0.05%) that prove year after year accuracies better than 0.25%. And the year after.

Most manufacturers back down from installed performance guarantee.

But accepting this challenge is how we achieved better performance. ■

You may be interested in the British Materials Handling Board publication - 'Guide to the Specification of Weighfeeder Systems' for information about specifications and a checklist to determine suitability. ■

Dear Bates,

Can you pls advice,where can I get hold of the British standards for weighfeeder systems.

Thanks,

P.J.Talreja ■

Copies of the document are available from: -

The British Materials Handling Board,

15 Harewood Avenue,

Sale,

Cheshire. M33 5BX price £ 15 plus £5 overseas postage.

or if you send your address to lyn@ajax.co.uk I will arrange a copy to be sent. ■

I asked a simple question part way through this thread, that is, how do you prove that the weigher is better than 0.25% accurate over a period of time. Accuracy at the time of testing is not a problem.

I see a number of claims that it is possible but no one has come up with the answer. I am not convinced there is one.

Jon Scarrott ■

It is practically not possible to have a high accuracy belt weigher with very low dynamic ranges. It is better to go in for a static weighing system line a throughput weigher which can give accuracies as 0.1%. This can be incorporated in series with the belt weighers. We have incorporated the same for tea industry for the drier output. ■

Dear Mr. Pilot,

It is very difficult to get an accuracy of 0.25 of FSD. Can you tell if I say this belt scale will give you an accuracy of 0.1 % of FSD -how can a person will veryfy it?

Regards.

A.Banerjee ■