Belt Scale

Are you taking random test samples of the load from start to finish to determine the average mass density of the coal after it arrives and comparing it to the pre shipment specs numbers?

If what they specify it at is way less than what you measure it at it is picking up the added mass along the way somehow. If not your belt scale is not as accurate as you think it is.

we haven't conducted any random samples. Might be along the way weight of rain water has added on the coal. we plan to hire a surveyor to conduct parallel measurement of the delivered coal before unloading..aside from that what would be the better way of conducting parallel testing? thank you for your quick response

It may also be possible that their scale is in error, in your favor.

Please describe your procedure for calibrating the belt scale.

Typical calibration involves zeroing the scale with no load, then applying a static cal weight to set the span. Yes, it's a calibration, but it's a static calibration.

How do you know the belt speed is accurate? How do you know the integrator's working properly?

When questions like this come up, the site gets a couple dump truck loads of material, weighs the loaded truck on a scale to get a reference weight.

The trucks' loads are then run on the scale to see what the scales' dynamic performance is.

Then a legitimate comparison can be made between a known weight that you've locally verified and the dynamic performance of the scale.

I concur with the other commentators and I have added some other points of my own commentary based on my own experiences.

There are many conditions that could affect you coal mass received. Listed in dot point are factors to consider.

1/ What was the moisture content at the Indonesian Weigh out?

2/ Was a supplied mass, water content, calorific value & specific gravity etc. record supplied for the product?

3/ Was the Indonesian Weighing machine in correct calibration at the time? Weigh Scale setups can and do change very quickly if a mechanical component change or fail or conveyor structure moves for whatever reason. If the weighing scale system is in error, have they added extra to make a perceived short fall in mass of product for whatever condition of product analysis?

4/ What was the moisture content of the coal received? Was it more than 3%?

5/ Has the Power Plant belt scale weigher been checked for alignment within the original parameters for designed installation?

6/ Has the Power Plant belt scale weigher correctly maintained to keep the total parameter specifications true and accurate under all operating conditions?

7/ Have either the Indonesian or the Power Plant been subjected to power corruptions or severe lightning storms which does interfere with data transfer in digital binary transfers to and from belt electronics & PLCs?

8/ Did someone make a documentation error in your favour by typing in incorrect data like 6,500 tonnes instead of 5,500 tonnes?

That would account for the 1.000 tonnes +/- .5% error at both ends which would = 6565 tonnes not including moisture content.

9/ Does the Indonesian coal deliver from their site as volumetric or is it weighed? That could be as much as 10% or more difference in mass. There is a complex formulae when checking mass within a stockpile area due to the compaction from the bottom upwards reducing as the pile height increases but remember it is not a constant ratio or value.

These dot points are many but not all the possibilities that can cause such errors.

I concur with TECMATE's assesment and have only one other thought and that is:

Has the aligment of the belt scale with the conveyor been checked, small misalignments can cause measurement errors

Is their invoice in metric tonnes and your scale measuring in English tons?

I also found an interesting article dealing with coals asbsorption capabilities.

http://www.saimm.co.za/Journal/v102n07p417.pdf

The particular coal is from South Africa but it can absorb as much as 50% moisture. Maybe the coal you recieving is similar.

To calibrate a belt scale build a frame that is wider than the belt and get several lengths of chain that are longer than the span between your scale rollers and hang them from the frame. Ensure the chains sit flat on the belt over the entire span of your roller scales. Calculate based on the size of chain, the number of chains and the length between scale rollers how much the chain weighs and then start the belt scale and see if it reports accurately. Be sure to zero the scale with the belt running with no additional load on the belt. I am wondering if your belt tension is too high and when empty and calibrating your belt weight is less than actual and then when loaded down with coal you are measuring belt weight plus coal weight.

Hello guys..thank you very much for sharing your ideas..

with regards to cacalibration, I could say that we calibrated the Belt Scale as near as the system accuracy. the system accuracy is 0.5 % and after we calibrated the BS (zero and span) we came up 0.14% accuracy. after the span calibration, we conducted a totalizing test in half hour. let the belt running with the static weight loaded on the weigh frame. As the current flow rate display is 711 T/hr. From this flow rate, we could predict that after 30 mins the total initial tons will be added by 711 tons. based on our test the initial is 50910 tons and after 30 mins it has acumulated to 51266 tons with difference of 356 tons. this the actual totalising.

we compared it to the computed totalizing whic is from the 711 tons/hr devided by 2 for half an hour and it arrives 355.5 tons. From these two data actual and computed we have calculated the accuracy.

I think the problem here is the measuring unit. our BS is in long ton measurment but the invoice is in short ton. thank you for your help guys..

Bakerjohn thank you for mentioning the metric tons and english tons..

God bless guys..