Unit Conversion for load cell

[pcbv]

Hi everyone,

I need some help from you.

I must measure the weight of a system. For this I use a NI DAQPad-6015 and SC – 2345 with SCC-SG24 and SCC-SG11 modules. As sensor I use a U2A load cell from HBM. This cell has the sensitivity 2mV/V and it can be used until 5t. I use 10 V for excitation voltage. The gage resistance is 356Ohm. I can measure the load cell output, with a good resolution, but I don’t know how I should convert this output to weight units (kilograms). Is there anybody who can offer me some information about this problem?

Thanks in advance.

[devchander]

You usually use a custom table scale, and do volt to load conversion ( using 2 point conversion)

This Link should give you a starting idea on how to use your sensitivity factor for unit conversion

This link [broken link removed] discusses about load cell mesurements in general

Also, you could start off with DAQ assistant ( if you are using LabVIEW, LabWindows) for your load cell measurment

any doubts, do ask

[devchander]

Also read this link 

An old post where conseils has given one elobrate answer! 

[pcbv]

Thank you very much for your answer.

I read the discussion and I made exactly as there.

But, the result that I obtained is not so good. I made a LabVIEW program in which I measure and convert the voltage, from the load cell, to weight unit but I obtain a less value that if I use a Hottinger instrument to measure. Than, I introduce the calibration module in the calculus, but unfortunately, I obtain less that first time. So, I think that I don’t make the conversion well. If I’m looking to the inscription on the cell I observe there is an approximation sign between the sensitivity and weight (in picture is 50Kg (I have a cell for 5t) @ 2mV/V) (see the attached picture). Maybe, this is the problem.

You discuss about the custom table scale. This means to put some weights and measure the output cell voltage and then put this table in the MAX in the custom scale?

Thank you again for your help.

Best regards

Message Edited by pcbv on 09-19-2006 02:08 AM

[devchander]

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You discuss about the custom table scale. This means to put some weights and measure the output cell voltage and then put this table in the MAX in the custom scale?

We used to calibrate a load cell and prepare its look up table.

It would be done in a calibration laboratory using standard reference equiment.

Also shunt calibration can be performed with a set of precision resistors to simulate a set of  loads that are spaced over the range of the load cell and use this resultant values in the the look up table.

But if you application does not need the entire range of load cell and does not need a very high level of accuracy, set two optimal load points ( high and low) measure its corresponding voltage signal and use it for custom scaling in MAX