9237 strain gauge setup using measurement & Automation

[abrown61]

I'm using a NI 9237 using a NI 9162 USB carrier and I have a question involving the setup of the strain gauge measurement using the measurement and Automation program, which I just recieved.

In the task window to setup the strain gauge, it ask for bridge config, gauge factor and  gauge resistance.

My question is that I already have calibrated strain gauges and have the cal of the strain gauge in mV/V for a given load.  Usingt the vex (voltage excitation value) I can come up with a scaling for the strain gauge to go from mv to newtons.  Do I just put this number in the scaling box and will the that be fine - or do I need to calibrate the system using the bridge config, gage factor and gauge resistance numbers - or do these only come into play if I usng the Measurement andautomation program to calibrate the strain gauge?

[J_Thomas]

Hi abrown61,

I am a bit confused? Are you using a strain gauge or a load cell (that may have a strain gauge on it)?

For a strain gauge:

To get the most accurate measurements, you should provide values for the gage factor, gage resistance, lead resistance, and especially the strain gauge configuration type.  This information is usually found on the manufacturer’s data sheet for the strain gauge.  These parameters will ensure that you get a proper strain reading. 

For a load cell:

I would recommend creating a DAQmx Custom Voltage with Excitation Task, because you have all the information that you need to scale your signal into Newtons based on the raw voltage reading.

In the DAQmx Custom Voltage with Excitation Task setup, look for the “Custom Scale” section and select “Create New” from the drop down menu.  You can then select a custom scale type and input values to define how the raw voltage should be scaled.

[jyothi prasad]

sir

i am using kistler load cell with range 1.11kN and sensitivity 4 mV/N.i have problem in creating the custom scaling.can u tell me based on the above values i have mentioned what will be the slope i have to give in linear scale.i am using NI 9237 DAQ.i have done experiment but the problem as soon as i start the experiment without any load it is showing 200N of load.how to overcome with this problem.

[The_Red_Barron]

Hi jyothi,

 If your prescaled units are Volts and your scaled units are Newtons then the slope of your scale should be 250.  I calculated this as follows:

(1 Newton)/(.004 Volts) = 250

Since you are reading 200N without any load connected you should set the Y-intercept to be -200 to account for the offset.

Regards,

[jyothi prasad]

thank you sir.initially i am a bit confused sir.you replay cleared all those confusions.