correct notation for using displacement sensors (piezoelectric) using nidaqmx in python

[eduardomp8]

I asked this question in stackoverflow... I haven't got a response yet.

This question is simple. If you want to use a piezoelectric sensor for vibration analysis, you need to enable the IEPE source.

There are currrently two different type of displacement sensors: the eddy probes, and an accelerometer that gives you a double integrated response signal.

From many different topics, I found that the correct notation for accelerometers, and velometers is (sensitivity, I assume is 100 mV per g for the accelerometer, and 100 mV per ips):

# for the accelerometer
task.ai_channels.add_ai_accel_chan(physical_channel = "your_card_name/ao1", sensitivity = 100, current_excit_val = 0.002)

# for the velocity sensor (once integrated):
task.ai_channels.add_ai_velocity_iepe_chan(physical_channel = "your_card_name/ai1", sensitivity = 100, current_excit_val = 0.002)

What is the correct notation for displacement (piezoelectric) sensors?

Or what can I do to get around this issue, would it be correct for me to assume the signal as an accelerometer, and do the double integration through software instead?

[santo_13]

What is the exact model of sensor you're using? and how is it connected to the DAQ?

[eduardomp8]

common piezoelectric sensors, like this one:

https://wilcoxon.com/pc420dpp-40-2/

I have right now a NI9234 and you just connect a cable (military plug with two pins) and the coaxial goes to the NI9234.

[santo_13]

Nope, these are not compatible.

Your sensor uses a 4-20mA current loop and not IEPE.

[eduardomp8]

it is my understanding that an IEPE source will give you 4-20 mA.

https://en.wikipedia.org/wiki/Integrated_Electronics_Piezo-Electric

by the way... we have another program in visual basic (not made by me) that uses this IEPE source to (correctly) power up these piezoelectric sensors... we have been using our cards with IEPE source for accelerometers, velometers, and displacement sensors. I am trying now with python, hence my question. 

[santo_13]

IEPE supplies a constant current and looks for variation in voltage, whereas 4-20mA loop provides a constant voltage and looks for variation in current to indicate a signal.

If a sensor supports IEPE, it will explicitly state 'IEPE' in the product page and 4-20mA is NOT IEPE.

https://wilcoxon.com/blog/4-20-ma-vs-iepe-vibration-sensors-for-control-systems/

[santo_13]

If you wish to just replicate what the visual basic program does, please post the code.

[eduardomp8]

Something happened to my previous response??

Thanks for the Info, now I know that IEPE and 4-20 mA power loop are not the same, and I found another page that explains the concept much better:

http://www.endevco.com/Our-Resources/Ask-the-Experts/Understanding-IEPE-accelerometers-vs-4-20-mA-se...

I cannot post the visual basic code, but I will ask the author about it, but he's probably using it as an accelerometer and integrating it twice via software, although, I will ask him and update in here.

And even if they are different, I can select the IEPE source to power up these piezoelectric sensors, and they will work fine (cannot use AC or DC sources on them)

Attached is an image of the program that I'm doing (using velometers) 

this is a little motor that I'm testing:

so... my question remains, do displacement piezoelectric sensors have a specific notation or should I treat them as accelerometers or velometers?

[eduardomp8 · Accepted solution]

Posting this so I won't misinform anyone.

I was talking with my father, he is the author of the visual basic code, he was telling me of my mistake, 4-20 mA power loops are absolutelty not the same as the IEPE sensors as I was previously informed in this community.

The sensors that we are using are specially designed to use IEPE sources. The sensor information that I provided in the first posts are not the ones that we are using. My father tells me that the displacement sensors using IEPE source (accelerometers that are double integrated) are kind of rare, so I am assuming that's the reason I can't find the notation for them.

I asked him how is he taking them into consideration in his program, and he is telling me that he uses everything as an accelerometer and he later integrates via software once for velometers, and twice for displacement sensors.

Apologies for the confusion, and use this as the accepted answer (I guess?)