Is the excitation voltage for NI9237 signal conditioning module in volts DC or volts AC rms.

[ClaireJ]

Hi there,

A simple question, please excuse my ignorance.

I am wondering if the excitation voltages (2, 3.3, 5 and 10V) for the 9237 signal conditioning module are quoted in volts DC or AC? 

My pressure transducer can accept up to 5V AC but only 1V DC excitation (which would make the 9237 module unsuitable).

Thanks for your help,

Claire

[Kyle_K]

The excitation voltage is DC voltage. The 9237 is intended for load cells or strain measurements that utilize a Wheatstone Bridge configuratioin. There is probably a more appropriate model for your pressure transducer. What model is it?

Kyle K.

[ClaireJ]

Hi Kyle,

The PT is a custom made needle mounted PT from Gaeltec (http://www.gaeltec.com/products/specials-general-purpose-transducer/needle-tip-pressure-transducer-N... The sensing face is a metal diaphragm with directly deposited resistive strain gauges. I have asked whether they are quarter, half or full-bridge (waiting on an answer). 

I can't see any bridge modules for the cDAQ that could supply a 1V DC excitation - do I need to move to the SCXI system? (my understanding is that even externally supplied excitation voltages must be >2V on the 9237).

Thanks,
Claire.

[Kyle_K]

Claire, 

The link is sending me to a failed resource and I cannot see any of the details of your device. It is possible that you may want a module that has analog input and analog output channels to read/power this device instead of a bridge module. It is also an option to power the sensor externally and independantly from the module. It all depends on what your goal is for the setup.

Kyle K.

[AnalogKid2DigitalMan]

Try this link:

http://www.gaeltec.com/products/specials-general-purpose-transducer/needle-tip-pressure-transducer-N...

-AK2DM

[ClaireJ]

Thanks for the functional link AK2DM.

Kyle, the transducer is definitely a bridge sensor (full-bridge), so needs excitation voltage supplied, unless we buy the strain gauge amplifier from the PT vendor (which I would prefer not to do). Can you recommend a module that can supply a 1V DC excitation? I was hoping to stick with the cDAQ range because thats what I used in my previous lab, but can move to SCXI if that works better for this application (my understanding is that it has all the same capabilities but is just less portable).

Thanks,
Claire.

[Kyle_K]

If you are looking for a single card to do it all simply, I would recommend the PXIe-4330. This can hit the lower excitation voltages you need and has the bridge measurement features available. It is a PXI system which is similar to SCXI but a newer design with more integration features for future expansion possabilities.

[AnalogKid2DigitalMan]

Can't you just use a separate 1VDC power supply to serve as an external excitation source and still use the NI9237 to sense the bridge?

-AK2DM

[Kyle_K]

The NI 9237 needs to have the excitation voltage pass through it in order to perform the bridge measurement. However, if you wanted to excite the bridge with a completely independant power source, you could use the NI 9219 since it has the ability to sense the voltage without being a full bridge measurement (a requirement of using independant excitation). Our bridge measurements monitor the power supplied to the bridge and compensate for fluctuations to improve accuracy. Using a voltage measurement instead of a bridge measurement will also require you to perform the conversion from mV to Pa (or whatever pressure unit you desire) progrommatically rather than letting our software perform the conversion automatically.

[ClaireJ]

Thanks to everyone that contributed to answering my question.

For anyone else facing the same issue, the two solutions I came up with were:

1) The manufacturer supplies a module that can reduce an excitation voltage >1V down to 0.9V

2) The PXI  6361 module (from the PXI rather than the cDAQ range) can supply excitation volatage <1V. 

I'm fortunate in that I am choosing a system from scratch, not trying to make do with the cDAQ 9237, so I have decided on the second option.

Again, thanks all for the contributions to the discussion.

Claire.