Calibration Procedure of Load Cells

What are you measuring the load of? Only coal - coal plus transport belt - coal + belt + frame and mechanical outfit? Do you have calibrated weights? Tell us something more. You can calibrate the load cells - or - your weighing process system.

Weigh nothing at all. Set zero to zero. Weigh a certified test weight. Set span accordingly. This may affect the the previous zero calibration.

Then, either 1) Solve some equations and adjust matters to match, or 2) repeat the foregoing steps until nothing changes....

you never calibrate the load cell before do you?

Hi "guest"!

CR4 gurus are a funny lot! Some of them know ALL about EVERYTHING !

Among them a few give an answer to ALL questions even if they only have a very basic knowledge of the subject they claim to master!

It is a sign of OVER ESTEEM and despise of the others.

But if you stay longer you will enjoy it and have fun!

What I wrote was intended for a bit of irony/humor. But it may be closer to the truth than you realize. Feel free to question my experience, if you like, but then explain your procedure, and why it is supposedly better.

There are standard procedures which make sure that the traceability (back to the national references) are respected. All depends on what the measurement is thought for:only for internal production analysis or for commercial actions.

You can either calibrate the cell alone or the sytem where the cell is incorporated but the procedure itself depends on the system and on the influences between system and cell.

I would suggest to take following steps:

- you buy the standards and use them for the calibration of cells out of the system (stand alone).

- you use the same basic principle for the calibration of weighing systems with cells build in

Normally you are obliged to determine the "uncertainty" of your measurements and several parameters as linearity, hysteresis and return to zero in order to qualify the class of your weighing.

It is not a procedure to apply as "some body" suggested you to do, it is procedure you must follow as the ISO defined it to be.

To give you a feeling: the cell has to be calibrated at least with 5 weights almost equally distributed within FS limits. 3 loadings up to 125% or 150% have to be done and only if the return to zero is within some limits the procedure can be continued. The weights have to be applied at controlled speed and the measurements have to be taken only when the variations are under a threshold. The load has to be increased & decreased 2x and the results have to be used for a computation form which is part of the standard.

As you see it is not so simple as some think it to be.

Where can I download a standard procedure that is defined by ISO? Plz help. Thnx

The manufacturer of your load cell should have this. If the load cell came with a manual, that is certainly part of it. Check for calibration. or go to his website. You can also check the weighing indicator manufacturer.

That is my problem right now. Our plant is still under construction. We are using Raumaster Oy coal feeder. My boss assigned me to make such procedure but i can't find any load cell documents. I don't know what is the maker of load cell being used. My boss suggested me to find from internet for any vendor. What site should I go? tnx

If your plant is still under construction, then all the contacts you need should be very close. Whose controlling the construction of our site? Go and see them and start knocking on some doors, it sounds as if your in a position where you need to have some get up and go. Be pollite, forcefull and persistent. Try contacting Raumaster Oy, the manufacturer of the coal feeder. Ask them if they have an engineer onsite, if not ask them if they could get one on site and, have all your questions ready for him. Ask him all about the operation of these feeders (I find it better to have a good understanding of the complete peice of equipment, even if I only need to know about a small part of that equipment), what the maintenance requirements are for them, especially the calibration of the weigh process. This company should be happy to send someone along, as I assume you've spent quite alot of money with them. If not, I think you've bought equipment from the wrong company. If Raumaster Oy can't answer all your questions, your in for a rough ride in the future (Rip it out and start again).

All the Best.

Go get Um.

You have to buy it it is not free as any standard and more than that it is forbidden to give it for free.

The load cell document does usually NOT have any description of the calibration procedure only the load cell uncertainty class and according to which standard it was defined (not always).

You say "...and more than that it is forbidden to give it for free."

I'm curious...what is the purpose of forbidding some one give it free to someone else. For instance a load cell manufacturer purchasing them and providing them free with to customers who use their load cells?

I wrote about STANDARDS not about procedures. may be it was not clear enough.

Regardless whether it's standards or procedures....my question stands. Why is it forbidden by law to give them away for free?

I can understand why the supplier of the standard isn't going to give it away as they they may want to recoup the cost of producing and maintaining the standard. But for it to be against the law for a load cell manufacturer to give away a standard that's related to a product they sell seems overly big-brotherish.

Perhaps I am over looking some useful purpose of such a law.

To maintain the organization which makes the standards it costs a lot of money which is recovered by selling the documents. If you give them for free then the whole organization could collapse. In the States you are less concerned about standards and this has some times a negative economic impact. In Europe for economic reasons standards are respected and BOUGHT although the prices are very high. It is a difference in the mentalities. I do not claim that one is better then the other. Standards are, if respected, guarantees for, among other, quality and reliability. With respect to the calibration. The manufacturer is obliged to issue a certificate and specify according to the standard he used several parameters which define the test conditions and the traceability. Coming back to "free" docs: What would happen if all books would be available for free ? What would happen if all services would be for free ? What would happen if you will work for nothing ? You get the point ?

We may be talking past each other.

If the maker of the standard wants to sell it, that's their business. It's a business decision (or should be). If it's expensive to make and manage, then by all means they should have the right to demand whatever the market will bear on their efforts. If the government is responsible for the standard, again, they can charge whatever they want.

If company A purchases 200 copies of the standard and wants to give them for free to their 200 best customers, how does that harm anyone economically?

One could make the argument that if an organization (governments, etc.) want standards to be followed, it would be in their best interest to provide them for free as a way to get the majority of companies following those standards.

I see nothing wrong with the government requiring certain standards to be followed and to charge for those standards. But why would the government care if some company (that no longer wants their purchased copy of the standard) gives it to me without charging me for it?

Check these sites: there are many different options - select on top of the page.

http://www.wipo.int/pctdb/en/wo.jsp?wo=2007104827

The information about the load cell(s) should be provided by them. You should specify all these details before acceptance of the goods.

In Europe, all machinery has to be certified. The safety manager, engineer or head of the safety department has to give permission to the goods receptionist to receive the goods. But it is his esponsibility to check if everything is according safety regulations and he has the duty to imply extra conditions, that are binding for the contract.

It is normal that the supplier provides an operation manual with parts list and specifications - that show details of parts, like safety materials, motors, mechanical parts and for sure the weighing part, which is a substantial part of a feeder, to determine the economics of the process.

If everything is in place, insist for delivery of written descriptions of the parts you are interested in, with references to all the suppliers too.

When your boss gives you that assignment, the first thing to go for is documentation.

Hi erolf,

I am familiar with Stock gravimetric and volumetric feeder/weighers on pulverised coal power plants but not familiar with Raumaster Oy. I suggest you contact them for exact details.

If your manager has asked to calibrate load cells for the feeder, the usual calibration for load cell devices would be followed for the operating range as in the above posts

If the task is to calibrate the feeder/weighers then it is a little more extensive. Given that the feeder/weighers are your measure of energy input to the process, with their output usually on a rate basis (kg/hr), any variation in fuel energy content (mJ/kg)will require a change in fuel feed rate. It is not unusual to have 1 gravimetric feeder and the remainder being volumetric feeders on a plant, so the accuracy of the gravimetric will influence the overall energy input. The gravimetric feeder measures the fuel weight over a fixed length of feeder belt, then adjustment to belt speed will provide desired fuel energy input. If the purpose of the calibration is a heat rate test, and particularly for a supplier/customer acceptance test, I would consult the ASME Power Test Codes for any prescribed requirements. If it is for your own confidence you should calibrate your load cells, then run the feeders with a measured amount of coal of a known/measured density characteristic to check that feeder output is within expected results.

A search on ASME and EPRI docuents on the topic will turn up a number of papers and discussions, usually related to boiler/turbine plant testing and R&D topics.

I agree with Aussie Bob to go back to Raumaster.

In addition to the loadcell calibration there will likely be dynamic mass calibration using coal catch scale or other verification method. The catch data will be fed back to the Raumaster controls for a span adjustment.

You can also consider feasibility study first (how many load cells do u have?) before attempting to build a capability for that. Sometimes it's better to have somebody else do that part for you (if cheaper), building capability will also cost some amount of money if you follow a standard (ISO), in any case you will need a standard (weights) for this and you will also need to have this calibrated to a higher standard (traceability)...

Can you use independent calibrator to do it? I don't think it cost much to calibrate the load cell and most of them would have equipment ready to it for you. Otherwise you may have to design your own equipment to do it, you may need to have hydraulic system which strong enough to full or push your nominate load and the reference gauges.

<...load cell calibration procedure?...>

The load cell ought to have a serial number on it. The documentation on this cell should include a manufacturer's calibration certificate, or a type test certificate for it. If these documents are absent, then get on the phone to the original equipment manufacturer and ask for copies of them to be faxed over.

If the cell is performing off-standard, then a second telephone call should provide access to the resource needed to have the cells recalibrated. Renewing the cells with a calibrated replacement set might be part of the procedure.

You need to have an original impedance spec sheets on the installed load cells. There should be a load box/controller for the load cells. When they are not in service, you will have to calibrate the load cells to the original impedances from the spec sheet on each load cell with the load box and tweak the impedance ranges accordingly.

The only other way to calibrate is to put a known weight/force standard on the cells and calibrate for accuracy.

I have made resistance bridges for the controllers to substitute for the load cells, and used these to calibrate the zero and full scale indicators.These resistors must be very high accuracy to be useful.I found some .05% wirewound ones.After calibrating zero and span at 20% and 80 %. the display can be used as the final reference for furthur calibration of the load cells, which is done by applying know weights to the system.