LVDT not reading

[alaspina]

Hello all, 

I have a Hampton VA HR 100 LVDT sensor. I want to measure the position of a rod within the LVDT sensor (displacement). I am new to Labview, but I managed to get a VI working. 

My first issue is that I cannot select the device as an LVDT Analog input, rather, it must be read as a Voltage input when I start up the DAQ assistant on the VI. That works, however, the movements of the rod seem to indicate an acceleration rather than a position change. I have attached the graph of the VI that I get for 10 samples at 100 Hz. I also attached the VI. I need to get it to read it as a position, hence the voltage reading should indicate a displacement, and not just go back down as soon as I stop moving the rod. 

I am using a NI USB-6009, with grounds connected to both the 5V pin digital side and the analog side. Any help is appreciated. 

Thanks. 

Alessandro Laspina. 

[Henrik_Volkers]

A LVDT need a constant amplitude sine exitation and a 'lock in'/sync readout to measure a distance. Can't supply a link, but get the physics on how the sensor work, and you migth find that it's hard to do with a 6009.

With the  software timed 150 SPS analog output of the 6009 I doupt that will get meaningfull readings without a LVDT signalcoditioner and a 6009 only. You can try an external sine generator and read LVDT  exitation and output ...I would try to use a soundcard to exite and read the LVDT 🙂

[alaspina]

I am fairly sure I am providing a sinuisoidal wave input, but did not understand the lock-in/sync part. Why would I need a soundcard? The current setup should work (as it was done before): Labview,  USB DAQ 6009, and a circuit board I forgot to mention that connects the LVDT coil to the DAQ card. This board has a few capacitors and resistors but also an amplifier. The pin connections are correct, as nothing else reads it. 

I am getting measurements whenever I rub the rub in the inner coil, but I think it isn't good in the long run for the sensor. 

The LVDT has 6 wires out. 

[Henrik_Volkers]

I can't open your vi, so I can't see what's going on.... and unless we don't know what yourboard is doing....

For a LVDT you supply a sine exitation, the output (if propper wired) is a sine proportional to the feeding amplitude and the displacement . The lock-in/sync detect on which side of the zero (center position) you are  (phase turn 180°)

if you read exitation and sensor output (with high samplerate and at least 10 periodes, you can apply a tone detection and calculate the amplitude ratio and phase difference (last to detect sign)

Around zero you will read any phase, depending on how good the sensor and setup is 😉

[alaspina]

For sample rate, how high is high? I am using the convetion of having at least double the amount of sample compared to Hertz. Hence, I noted that the HR100 LVDT sensor is tested at a frequency of 2.5kHz. So I select 2.5kHz and provide 5500 as the sample rate.

I have tried now doing a voltage input with a sine wave excitation when using the DAQ assistant as opposed to just the Voltage input. 

I have reattached the VI, let me know if you can open it.