load cell scale

[satyamgajjar]

I am new to Labview and trying to set up load cell for our beam behavior for different loading. I am using PCI-6035E for my 100 lb load cell. I have tried with Map range and Table values for scale values conversion but still I am not getting results. Its shows greater increasing values without applying load. Herewith I am attaching load cell calibration report. Thank you in advance and kindly help me to go with my first project.

[Conseils]

A thought....
The basic calibration factor is around 0.2993mV per lb force.

So as the PCI-6035E is an aquisition device, how are you supplying power to the Load Cell, in the calibration it was powered with a 10.000v supply. If the supply is not hight quality then this could be the source of your errors.

Are you trying to use the DAC output for the device supply?

[satyamgajjar]

Thank you for your reply,
I am using strain gauge conditioner for 10.0 v excitation voltage. When I calibrate with the load cell - it shows minor voltage without applying any weight.

I have tried with map ranges and table values but for both of them its shows some results without applying any weight.

kindly advice me with the scale and my instruments

[Conseils]

This is called an offsett and is nothing to worry about. It's a result of the gauges not being perfectly balanced, but this is standard. See the calibration sheet to see the difference in resistances.

Basically all you have to do is subtract this offsett from the value obtained with your test weights. Your reading relative. What you will find is that this value can move as a result of a number of factors and you may even find that if you turn the gauge upside down the reading will change. Temperature should have a very small influence as in theory the gauges are compensated but it depends on the application.

[jwhite]

I also have a similar question.  I have two of the same load cells but I am getting erroneous data also.  One will "zero out" when no load is applied while the other shows about .05 lbs without a load applied.  When I unplug the sensors, and switch them (using the opposite SG24 module) I get opposite results.  The sensor that had showed "zero" now shows a slight load.  Is this a problem with one of the modules?

Also you mentiioned subtracting the offset from my reading to account for the error.  However, the one load cell that will not "zero" has a lower reading when the mass is applied.  In other words, the load cell starts out at .05 lbs with no weight, but the final reading (with mass applied) is way less.  I don't know if this has anything to do with it, but the calibration sheet of each sensor has a "zero balance" listed in mV/V.  Does this affect how the sensor is "zeroed" with no load applied?

Thanks,

Jason

[johnsold]

Jason,

It sounds as though your two load cells are slightly different in both offset and "gain" or full scale output. The offset differences produce the zero differences and the scale factor differences produce the differences under load. This is not unusual. Pick eight resistors out of a bin and make two bridges. You will get different voltages from the nominal zero due to resistance tolerances. Similarly the full scale changes will not be identical for the two bridges. For high quality measurements you will need to make separate zero and full scale calibrations for each sensor.

Lynn

[jwhite]

Thanks for the help.  Yes, that is the case with these sensors.  According to the specs one sensor has a "zero balance" of .0056 mV/V with a 2.000 mV/V output and the input/output resistances are 377.8 and 352.5 respectively..  The other sensor has a -0.0166mV/V "zero balance" and a rated output of 2.292 mV/V and the input/ouput resistances are 377.7 and 352.8 ohms respectively.  I used these outputs in the scales that I set up for each sensor, but I don't know how the "zero balance" affects my measurements (if at all).  When making the separate zero and full scale calibrations should I use the calibration tab in MAX?  If not, how can I adjust these sensors?

Jason

[johnsold]

I don't have MAX so I cannot help with that.

Lynn

[Adam W]

Hi Jason,

You may want to take a look at this Knowledge Base:
http://digital.ni.com/public.nsf/allkb/d22b70f72c3fb23286256f15005c2575

Also, the Calibrate button in MAX will take you to the Calibration Wizard.  The Help buttons in the wizard provide more information about different settings and expected inputs and outputs.

Hope this helps!

Adam W
National Instruments