Calibration of large tanks weight indicators

GOOD VALIDATION PRACTICE (cGVP) ISO 17025 - GENERAL METROLOGY, MEASUREMENT DEVICE,
1

Hi Everyone,

Hope those technical people out there can help;

We have large process tanks (15,000L) capacity, which have load cells and display. We calibrated the load cells/display by filling tank with calibrated flow meter. The problem is it takes a lot of time and water to fill these tanks.
We have gotten a company in to do a ‘forced calibrations’ by applying pressure/weight to the actual load cells, which they read off their own calibrated test rig.

as an experiment we carried out a forced calibration and then ‘checked’ it with the normal calibration with flow meter, thinking there would be no error, seeing as the forced calibration had a higher accuracy.

Does anyone have any thoughts on this? the forced calibration was supposed to have an accuracy of approx 0.1% and the normal flowmeter method approx 0.3%

thanks and regards
NK

2

This is my opinion about your situation.
You meant that they tested your tanks with their own equipment connected to the load cells without verifying the display on the tank? Every time I do the calibrations I try to verify of the system as whole. And if something doesn’t come out right, then I break the system apart and test each part separately. In your case you would have the load cells and the read-out part. While they test both parts in the process I would be Ok with it. also you should consider diference between the mechanical process of weighing things in the tank and the force pressure applied to the cells. I would need more details for a more complete opinion.