I've been preparing a project to carry out automatic weighing for some time now, and I've been getting information about the load cells, their characteristics, etc. I have found a lot of information in this forum or on manufacturers' pages about the parameters that characterize a load cell, how to select it, the sensitivity, the accuracy, the number of divisions, etc. However, I still have an important question.
Normally, when I buy a laboratory balance, the manufacturer tells me the maximum weight (e.g. 250 grams), and something like the readability, e.g. 0.01 grams. This way I know that I can weigh elements from 0.01 grams. What parameters of a load cell data sheet would I need to review, or what I calculate to do, to get this information?
I've been preparing a project to carry out automatic weighing for some time now, and I've been getting information about the load cells, their characteristics, etc. I have found a lot of information in this forum or on manufacturers' pages about the parameters that characterize a load cell, how to select it, the sensitivity, the accuracy, the number of divisions, etc. However, I still have an important question.
Normally, when I buy a laboratory balance, the manufacturer tells me the maximum weight (e.g. 250 grams), and something like the readability, e.g. 0.01 grams. This way I know that I can weigh elements from 0.01 grams. What parameters of a load cell data sheet would I need to review, or what I calculate to do, to get this information?
Thanks and Kind regards,
Alex.
That information is only available after you connect the load cell to YOUR circuit and after you have calibrated it. It will be different for every installation.
Thanks, Paul.
When I calibrate the scale, I set the zero value, and I test the values for 100 grams (for example). In the code, I can select the number of decimals to show. How to determinate the number of decimals I can show? Does it depend, for example, on the variability of the reading? If, for example, I indicate three decimal places, and these vary continuously, does this indicate to me that the precision of the balance is not enough to show me the three decimal places, and should I try with two?
Thanks!
Alex.
I worked at a research lab for 23 years. we had to develop in house testing, because manufacturer specs did not take our requirements into account
one aspect of testing is repeatability. you test at 500 pound, 1000 pounds, 5000 pounds. literal 500 pound blocks, with an eye on top, and "500 pounds" painted on them, like something out of a road runner cartoon.
if you get 10 mv at 500 pounds at 8 AM, 10.057 at 10 AM, 10.049 at noon, it is pointless to go beyond 2 decimal points. same sensor, same excite voltage, inconsistent results, and the last digit is suspect but included so you know which way to round the last reliable measurement
this is a Wheatstone bridge. it is designed to feed a differential amplifier. it should return 0 volts with no stress, positive voltage if stressed in one direction, and negative voltage if stressed in the opposite direction
alacecho:
What parameters of a load cell data sheet would I need to review, or what I calculate to do, to get this information?
The important parameters for pretty much any analog sensor are precision (ie resolution), accuracy
(including linearity),
repeatability and drift/aging, temperature dependence, supply voltage dependence, absolute
maximum stress ratings.
If you want guaranteed accuracy you'd normally need to pay for regular calibration.
The datasheet for a loadcell ought to have a variety of parameters relating to these fundamental
properties of a sensor.
Many loadcells are only accurate if correctly mounted - the force to be measured must be applied
along the right axis - this may mean a bearing system is needed to ensure proper behaviour
