Correct resolution of the device

[Oleks]

Hello all,

I am trying to understand if I am setting the resolution of my loadcell appropriately. If somebody have a spare time could you please give me some feedback.

This is what I know:  LC nominal output is +/-0.5348 mV/V and requires 10V excitation.  Applied load of +/-115N(Max) provides +/-5.348mV of the LC output.

Thus 1µV = 0.021N.

What I am confused about is the following. After I connect LC to SG24 unit that has 10V excitation and 100 gain, do I still have relation between µV and Newtons as before or should I recalculate it according to that 100 gain, such as:

Applied load of +/-115N(Max) provides +/-534.8mV of the LC output and leads to 1µV = 0.000021N ?

From sg24 signal goes to pxi 6221, which has 4 ranges/resolutions, so my understanding is once relation µV and Newtons is correctly calculated to get resolution of LC in certain range of PXI unit, say (+/- 200mV -> 6.4µV resolution) , I just need to multiply my value of 1µV by 6.4.

Thank you in advance

[Jordan F · Accepted solution]

There is a gain of 100 on the SCC-SG24 but this will be transparent to the voltage you will see when aquiring in your program.  The reason for the amplification is to utilize the full range of the ADC on the PXI-6221.  So, your input signal seen by the the PXI-6221 will be (max) 5.348mV*100 = 534.8mV.  If you set the range on the PXI-6221 to be +/-1V then you will be able to have a pretty high resolution on the amplified signal (2V/2^16 =  30.5 uV).  However, the signal you will see output will be scaled back down in the software back to the 5.348mV as was seen initially by the SG24.  No conversion is neccessary. 

[Oleks]

Thank you very much Jordan,

So that would mean that the resolution of 30.5uV will be the minimal "step" on +/- 5.348mV  range, and minimal force that my sensor will be able to read is 0.021x30.5uV = 0.64N, with 350 steps from  - 5.348mV  to +5.348mV , is this correct way of thinking?

Thanks again! 

[Jordan F]

The minimum step size will be 30.5uV when you are using a range of +/-1V but the signal that the daq card will see will be 5.348mV*100 (because the amplifier on the SG24) or 534.8mV.  So, there will be 534.8mV*2 / 30.5uV resolution which equals 35068 steps for your signal. 

[Oleks]

Ah, I see it now,

The range and accuracy is always defined by the setting on the DAQ board.

Thank you again!