What is the meaning of mV/V for loadcells? How do I calculate the resolution of a weighing system using it.?

Answer 1

The specification has to do with the full-load signal voltage to the excitation voltage. That is, a load cell with a 3mV/V specification will give a 3mV signal when the load on the cell is at full scale and the excitation voltage is 1V.

The resolution of the system is usually a function of the resolution of the signal monitor, frequently an analog to digital converter. If the analog to digital converter is an N-bit device with a range of R, the load cell has a mV/V rating of G and a full-scale rating of W, and the excitation voltage is V, then the resolution would be

Res = (W*R)/(2^N*V*G)

So, for a 12-bit ADC with a range of +/-1V and a load cell with a full scale load rating of 250 lbs (1112 N), a 3mV/V specification, and a 12V excitation voltage

Res = (250*2)/(4096*12*0.003) = 3.4 lbs (15.1 N)

Answer 2

Load cells use strain gauges to measure the small amount of compression or elongation in the metal element performing the 'weighing'. The strain gauges are designed to be put into a wheatstone bridge circuit (google the wikipedia article: wheatstone bridge for more details).

The bridge has an excitation input and an output. The output is proportional to the excitation voltage as well as to the applied strain -- which is related to the applied weight.

The mV/V rating is the proportionality constant for the bridge itself. If the excitation voltage is 5 volts then the expected output will be so many mV per 5 V. If the excitation voltage is 10 V, then the output will be so many mV per 10V.

You need to know what the output will be, so you can adjust the bridge amplifier accordingly.

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Answer 3

mV/V indicates the output is ratiometric.

Ratiometric means that the output is proportional to the supply voltage.

So 10mV/V mean that for a constant load applied to the cell the output voltage will change as the supply voltage changes.

Say 10 pounds provides 10mV @ 1V , this same load of 10 pounds will produce 20mV when the supply voltage is raised to 2 volts.

Resolution depends on the transfer function of the load cell usually a simple y=mx+b function where m = slope(gain) of the device and b is an offset if any.

(The gain is mV/V which will determine the span of loading to get full scale deflection) For example do you go from 0V to Vss using 100 or 1000 pounds?

Further efffecting resolution is the type of Digital to Analog (DAC) conversion. 8,12,16 bit etc...

The number of bits in the DAC determine the smallest change in voltage that can be resolved by the DAC. THe more bits the smaller the fractional change of the sensor voltage compared to the reference voltage which may be detected.


So to fully answer your question you need to provide the transfer function of the load cell,the bit size of the DAC , the Vss and reference voltage applied to the DAC

Answer 4

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RE:
What is the meaning of mV/V for loadcells? How do I calculate the resolution of a weighing system using it.?

Answer 5

Mv To Volts

Answer 6

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