Position measurement cdaq

[mbane]

Is there an I/O module compatible with cDAQ 9178 chassis, which is capable to acquire signals from displacement transducers (LVDT). I have looked the specifications for all the modules with and I can't find suitable according to product specifications. The tutorial about position measurement says 9229 is used in position measurement, but DAQ assistant won’t create a position measurement task with this device. Is there a third party module?

[Matyas]

Hi Mbane,

Generally, NI doesn't have a dedicated C series module for LVDT.

I think you can't avoid external hardware for excitation. Simply using an analog output for excitation then a simulataneously sampled module for input would work, but the NI 9263 cannot drive enough current for those sensors (100 mA)

You can excite using an external power supply and then use one of your faster simultaneous sampled cards though (i.e.: 9229). This should work just fine.

Depending on your LVDT sensor (if 20 mA excitation is enough) you could do your own calculations. If the compact DAQ form-factor is necessary, you will run into some difficulties but you could use a DAQ card to simultaneously perform analog output and analog input and then programmatically find the displacement yourself. The signal you would need to output is a constant AC signal to excite the primary coil of the LVDT and then you would need to acquire both the signal you output and then the LVDT response from the coils. You could then programmatically find the phase shift and amplitude changes between the two AC signals and compute the displacement.

Good luck with it!

Regards,

Matyas

[mbane]

Thank you for your response,
But I have further questions. I have HBM displacement transducers with following

specifications:

Nominal output signal at nominal displacement with output unloaded  80 mV/V
Nominal excitation voltage  2.5 V

Operating range of the excitation voltage  0.5...10 V.

So if I analyse the specifications for 9237 its maximal total power is 150  mV.

If I use exication up to 1.5 V, I should get the signal from the transducer.

9219 has even greater maximum total power so it can be used with execution
voltage 2.5 V.

Is my logic correct? I don’t see any limitations for using these modules.

Can 9229 provide excitation voltage?

[mbane]

Furthermore,

acording to post http://forums.ni.com/ni/board/message?board.id=250&message.id=54149&requireLogin=False it is possible to use 9205 for LDVT measurement. It is the same logic as described in previous post, but 9205 has several programble input ranges, so it is more suitable than 9237 and 9219.