accelerometer on 9237

[serbring]

Hello guys,

I would like to wire a strain gauge based accelerometer to a NI 9237. The accelerometer is this one:

http://img834.imageshack.us/i/accelerometer.jpg/

 I'm using labview signal express and I have added strain signal type, but the signal is noisy. How can I add an acceleration signal type?. Anyway I have also tried to add a "custom voltage with excitation" signal type, but it accepts only +/- 25mV full scale voltage and also in this condition the signal is noisy. How can I improve the signal quality?

thanks

[sisu84]

Hi serbring,

9237 is not able to measure your sensor signal because it is bridge module.

You have to excite your sensor with an external power supply and read your signal as an analog input with an other NI module.

Ciao!

[ZachHindes]

Hi guys!

First, the 9237 is able to measure this sensor since that sensor is a bridge, which is what the 9237 is designed to measure!

Now, to answer your question, I'm not sure why the signal is noisy, it could be connection problems.  That being said, Strain is not the channel type you want to be using, I suspect.  It sounds to me like this sensor is basically a Force sensor that you can deduce Acceleration from.  In NI-DAQmx 9.1 we added a few Bridge channel types to NI-DAQmx, one of which is Force.  With that channel type you can input the scaling parameters of your sensor (that gets you to Force) and add a custom scale on top of that to get to Acceleration.  Unfortunately, that picture isn't clear on how the sensor scales.

(NOTE: If you don't have/want to upgrade to NI-DAQmx 9.1 or later, Custom Voltage w/ Excitation would also work.  You would just need to do the scaling from V/V to Force to Acceleration yourself).

[LC3]

I am doing a similar setup (bridge accelerometer with the NI 9237) and after much time am still not able to get it all working correctly. I am using the Configure Scale to scale the electrical parameters to the physical. I have tried a few different things with my inputs and I just don't believe I am getting correct acceleration values. The sensor (an endevco 7264) correlates electrical units to acceleration in gs - y(mV)=0.1970mV/g*x(g)+2.9mV. That puts the physical unit on the x axis whereas NI 9237 puts the physical units on the y so I did have to switch the equation around. Also, the electrical input is supposed to be in units of mV/V or V/V and so I am not sure if that is where my issue?

In addition to just getting the scaling correct, I seem to be having issues with the signal input range. The DAQ assistant forces me to adjust those limits so not really understanding what those are based on. 

Thanks in advance

[Henrik_Volkers]

Have a look at the supplied calibration sheet.

The choose a matching excitation voltage.

If sensitivity is given in (m)V/g instead of (m)V/(Vg)  ... the excitation voltage is noted in the cal sheet and you can calc the (m)V/(Vg) value if needed.

[Henrik_Volkers]

And about SNR: If you have 10V excitation calibration data ... use 10V 🙂

Is the cable directly attached to the sensor? 

(triboelectric effects in poor cables can add noise)