Originally Posted by P.J.Talreja

Dear All,

For designing an automatic calibration system for an hopper weighing system of capacity approx 50 MT,what would be the minimum weight required to be paced for calibrating the hopper?

Generally what are the systems in the industry for achieving automatic calibation systems.

i have this problem too,but i found a recommendation from oiml(recommendation 107 discontinous totalizing automatic weighing instruments ) as totalizing hopper weighers,altough this topic is very old,but i think it may be useful to continue that...i think first point in hopper calibration system would be simulation,it means loading of weights on top of bulk is not correct,but discharging a bulk of a discrete measured load such cement or so can show better results... ■

Originally Posted by P.J.Talreja

Dear All,

For designing an automatic calibration system for an hopper weighing system of capacity approx 50 MT,what would be the minimum weight required to be paced for calibrating the hopper?

Generally what are the systems in the industry for achieving automatic calibation systems.

dont you hang a known weight on the hopper to calibrate it? ■

Originally Posted by lzaharis

dont you hang a known weight on the hopper to calibrate it?

no...hopper has an automatic weighing system,it means it doesnt require the intervention of an operator during weighing process....i think simulation should be implement... ■

In the US, the minimum test weight required for a bin scale is 12.5% of scale capacity. Automatic Bulk Weighing systems require 10% test weights.

as per Handbook 44.

http://ts.nist.gov/WeightsAndMeasure...ons/H44-09.cfm

look at sections 2.20 and 2.24 ■

thnx,it was perfect,...

you know,calibration & adjustment are different...i think for calibration we should use a discrete measured load,but for adjustment we can simulate by weight loading...

what`s your opinon? ■

We have used the Hardy Instruments C2 loadcells because they can calibrate without using test weights. They pre-calibrate the loadcell, store the calibration information on the C2 chip, and their loadcell amplifier retrieves the information.

Click for info: http://www.hardyinst.com/processwei...c+calibration/

We have found the C2 calibration to be just as accurate as using 5% – 10% calibration weights, and the C2 cal can be more accurate if there are linearity problems with the loadcell installation.

Regards, Delmar Schmidt

Melfi Technologies Houston

http://www.melfitechnologies.com ■

[QUOTE=Delmar;56970]We have used the Hardy Instruments C2 loadcells because they can calibrate without using test weights. They pre-calibrate the loadcell, store the calibration information on the C2 chip, and their loadcell amplifier retrieves the information.

digital loadcells are good,but some professions believe digital loadcell can`t show defects of a loadcell & when we encounter a problem,knowing wich one is fault is hard...[QUOTE=Delmar;56970] ■

Could not agree with you more. Our core business is retrofitting proprietary digital/LVDT loadcells and electronics (especially on LIW feeders) that become obsolete or cannot be supported by plant maintenance personnel.

The Hardy loadcell is a conventional 350 ohm, strain gage analog device. The C2 technology is external, and in the rare event the C2 chip would fail the loadcell can be checked with a multimeter and the system calibrated with movable test weights.

Regards, Delmar Schmidt

Melfi Technologies Houston

http://www.melfitechnologies.com ■

Mr. Schmidt,

Just off the cuff, my main concern with using a factory loadcell calibration as a reference would be that the loadcell must have a absolutely plum and true mount. Any misaligment will change the output characteristics of the loadcell. By using test weights, the output of the entire system is checked using a traceable reference that takes into account the characteristics of the complete hopper. If digital loadcells can compensate for the structure of the hopper, then piping connections, checkrods, or load deflection should never be a concern either. I don't want to disavow digital loadcells, but there is something to had from testing with an external reference. ■

The use of the increment method can be used on Hopper Scales and is very good at providing confidence and assurance the complete range of the hopper is accurate and linear.

This also allows for less test weights.

Just calibrate the first 10% of the capacity with the weights, remove weights, add material to the value of the test weights, then add test weights...etc etc. ■