Ni 9237, c series card

[Rameshs]

Hello

           iam using Ni9237 card and iam using an 100kg load cell My objective is to measure a weight btw 0 - 50 kg.

iexcitation voltage is 5 v. Sensitivity of the load cell is 2mv/v. reading i get for 0 kg is 0.000646431** v/v  

and for 50 kg is 0.00116299** v/v . will i be able measure a weight in grams (or atleast 10 grams ) .

** Places of digit i have mentioned in bold are fluctuating  .

[Ankur Jain]

Please confirm the Load Cell specifications

Excitation Voltage = 5 V

Rated Output = 2mV/V

Rated Capacity = 100 Kg

100 Kg Load => 10mV output => 10mV/5V = 2mV/V Output

In your setup, a 50 Kg load instead of 0.00116299 v/V = 1.16299 mV/V

So a 1 g load should give you around 20 nV/V output. Lets see whether it is feasible in NI 9237

As per NI 9237 specifications, the Scaling coefficient = 2.9802 nV/V per LSB (ADC = 24 bits = 2²⁴ Levels)

So 20nV/V output lies within the detectable range of NI 9237. You should be able to measure the weight in grams.

[Rameshs]

Hi Ankur,

              The card has a resolution of 24 bits, but the accuracy is 0.038 mv/v. Is it possible then ?. The value which i have got  fluctuations in the later digits is it because of the accuracy. 

[Ankur Jain · Accepted solution]

Yes, the variation in measurement may be primarily due to accuracy.

I think that load cell specifications contain accuracy details. Generally it is in % of maximum rated weight.

Trust that helps

[hurch]

Good day
I am to write a code that will read data from two NI 9237 modules (6 channels in total). the modules are to read data from a force balance (strain due to force).

I know its not a matlab community but I could get help, how do I convert strain result to force using a loadcell of specification stated below and the NI 9237. being specific, I need the coefficient to convert strain value given by the daq to force.

Load Cell: STA-7 Aluminum Alloy S Type Low Range Tension/Compression Load Cell

Rated load (kg)                      1, 2, 5, 10, 25, 50
Ultimate breaking load         300% of rated load
Maximum transverse load   <50% of rated load
Output/ Sensitivity                2mV/V (±0.1%)
Zero balance              <±1% of rated load
Excitation voltage                  10vdc recommended, 15vdc maximum

ch6.BridgeMode = 'Full';
ch6.ExcitationVoltage = 10;
ch6.NominalBridgeResistance = 350;