Excitation voltage

[KumarR]

Hello all,

I have recently calibrated a 4 component microbalance using Labview 8.6 and DAQmx. The four components in the balance are basically four full bridges. I performed calibration with default excitation voltage of 2.5V. I also calibrated using EV = 10V.

My question is simple one.

Is there a way that I get calibration results independent of Excitation Voltage?

In other words, Can I use calibration results obtained using EV = 2.5V with excitation voltage other than 2.5V

Thanks

[Henrik_Volkers]

The sensitivity of a bridge is usually measured (and calibrated) in mV/V per unit  where the mV is for the signal and the V for the excitation.

Check it with your results , it shouldn't differ that much 😉

For best calibration results you should do the calibration with the excitation normally used, because there are effects like self heating that can cause nonlinearities. 

[KumarR]

Hi Henrik,

Greatly appreciate your reply.

The signal I am getting right now is in mV. In the process of calibration I plotted load in (grams) Vs signal in mV. Now you mean to say I'll be plotting load Vs mV/V? And to get signal in mV/V, do I divide signal by excitation voltage after I get the signal in mV? or there is some way to get the signal already in mV/V?

Thanks

Rajeev 

[Mr.F]

Hi Kumar,

Henrik is right, usually a bridge is measure in mV/V. Some devices, like the NI 9237, will automatically return that ratiometric value.  Of course you could separate the excitation and measurement values by providing your own excitation and directly measuring your signal.  If you measured your signal at 2.5 V excitation and calibrated that with your load, if you change to 10 V excitation you should get very close to 4 times that same mV reading (differences due to self heating, random error, etc.). In short, yes, divide the signal you measure by the excitation voltage or use a NI 9237 which does it in hardware. Also, as Henrik implied you should calibrate you system as the planned excitation levels if you can.