Can NI USB 4432 read voltage i.e. conditioned NCDT signal

[m_tahir_m]

Hi,

As for as I understood that USB 4432 inputs are to read IEPE accelerometers signal. Can I read a conditioned voltage signal from my NCDT sensor i.e by using the option "IEPE-off with AC coupling"

Thanks

[CharlesD]

Hello,

So Yes you could turn off IEPE and select AC Coupling as these two features are software-selectable on the USB-4432 and read any Voltage signal.  Depending on sensor ouput however the accuracy of the measurement may be different.  

What kind of signal does your NCDT (Non-contact deisplacement Transducer????) sensor output?  It is important to keep in mind that all of our Dynamic Signal Analyzers (DSA) equipment use a delta-sigma ADC and therefore are very accurate in measuring relative signals or changes in a given signals.  If you are expecting to get a very accurate measurement at a particular signal value, this is NOT the best card, more specifically if you are expecting 5V, this card will not be accurate enough to read 5V exactly, however it will measure a change from 5V -6V very accurately.  Remember that these devices are mainly used for relative measurements of Dynamic Signals.  This is why these cards are often used to measure signals in terms of decibals - a ratio of two values.

Give us a bit more information on your sensor output and we will see if this card is appropriate for you!

[Sound Tech]

I had a hard time finding out about how to select/deselect the IEPE option as well.  In signal express is this option automatically selected?

[CharlesD]

In LabVIEW Signal Express you need to use either a Custom Voltage with Excitation task or use an acceleration or strain task to configure the excitation level.  The Normal voltage task unfortunately does not allow you to configure this as there is a Custom Voltage with Excitation Task already created for you.  Simply choose internal excitation and specify 2.1 mA (from the specs page) as the excitation level.   This should get you going!

[m_tahir_m]

Thank you very much CharlesD for your abrupt response.

Let me make my point more clear to you. I need to develop a portable system
i.e using a laptop PC with NI USB DAQ board which can monitor the following

1: accelerometer signal with builtin signal conditioning for the sensor

2: NCDT displacement voltage varying signal of some rotor of less than 200 Hz
and note that it is already conditioned by some external hardware i.e.
builtin signal conditioning for the sensor is not required from NI USB DAQ
in this case.

3: Also Digital Triggering of data is required for phase reference of data

4: Tachometer measurement is also required...both analog and digiatl
 

Initially, I intend to have the following items for the above mentioned requirement,
which looks to me a straight forward selection.

A: Chassis: cDAQ-9172 8-slot USB 2.0 Chassis for CompactDAQ

B: C-series Modules:

 NI 9234 - Accelerometer/Microphone Module
 NI 9229 - Proximity Probe (displacement sensor)  Module
 NI 9221 - Tachometer Module

But I am feeling that I can meet my above mentioned all four requirements with
a laptop PC alongwith the NI USB 4432. I simply wanna monitor the condition of
machines by measuring common vibration signals...acceleration, velocity, displacement
with phase info of acquired data alongwith the tachmeter signal.

Now my question is simple and hopefully be very clear that am i thinking right
as I prefer to have the system with 4432.please assume that all the signal ranges
are within the limits of 4432 and it is understood that IEPE is only to excite
specific type of accelerometers.

Thanks and best regards.

[gaving]

     hmmm, The only part about using a CompactDAQ chassis is that it does not have native digital triggering, which you said you needed.  I believe that you have to use a digital cSeries module (like the 9205) to have a digital trigger in your chassis. Also, the 9234 and 9229 can only sample up to a rate of around 50kHz, which is fine for everything but (possibly) your microphone, depending on what frequencies you want to sample.

     The 4432 could be configured as follows:

•  Accelerometer Channel (IEPE on, AC coupling)
•  NCDT Channel (IEPE off, DC Coupling)
•  Tachometer Channel (IEPE off, DC Coupling)
•  Use the digital PFI connector on the back to trigger your acquisition of all three channels.  (i.e. all three channels in one task and set the digital trigger to one of the PFI lines) (This may be a little difficult to do using Signal Express. (I'll try it out next Monday and let you know) You might want to consider using C or LabVIEW to configure your channels easier)

     Even if I'm totally off on the channel couplings or excitation values, you can see that this board would work for your application from what you described.

     Are there any other requirements of your system that I haven't considered?  Maybe discuss how the board will be triggered so we can be absolutely sure this will satisfy your requirements.

Thanks

-Gavin Goodrich

National Instruments

Message Edited by gaving on 05-30-2009 12:21 PM

[preston_johnson]

So Gavin has laid out the DAQ settings for you correctly.  For rotating machinery measurements, the trigger feature is really using the rising edge (or falling edge of the tachometer channel) as a phase measurement reference so you can see the phase and magnitude of the accelerometers and the displacement (proximity probes) that monitor vibraiton on the shaft. 

In signal express, you could do a frequency or tone measurement to get speed from the tachometer, yet the phase measurements as compared to the tachometer will be difficult.

The tool that will provide the best help is the Sound and Vibration Measurement Suite which provides a full suite of rotating machinery vibration functions including tachometer, orbit plot, order spectrum, and order tracking. 

http://www.ni.com/trysv/

[m_tahir_m]

Thank you guys

.

1. What about if I use the 5th cahannel of 4432 to read square wave pulse width  ,i.e. signal from digiatl tachometer using any software function from labview or Sound and Vibration Measurement Suite. if yes, how accurate will it be to read frequency (speed) as compared to from counters modules.

2. Is digital trigger available to trigger analog acquisitions. if yes, is it possibel to read all 5 chanels togather in one task.

3. If there exists a single PFI then  is it possible to trigger two different tasks , say  a task of 02 chanels with rising edge and another task of 02 channels with the falling edge of the same PFI.

Best Regards

[gaving · Accepted solution]

1. What about if I use the 5th cahannel of 4432 to read square wave pulse width  ,i.e. signal from digital tachometer using any software function from labview or Sound and Vibration Measurement Suite. if yes, how accurate will it be to read frequency (speed) as compared to from counters modules.

The 5th channel is the same as the other channels of the 4432 except it lacks TEDS and IEPE excitation.  I can't really say how "accurate" it will be at faster rates due to the delta-sigma ADC. Anyone else want to chime in on that one??  

2. Is digital trigger available to trigger analog acquisitions. if yes, is it possibel to read all 5 chanels togather in one task.

you betcha!

3. If there exists a single PFI then  is it possible to trigger two different tasks , say  a task of 02 chanels with rising edge and another task of 02 channels with the falling edge of the same PFI.

There are 8 PFI lines, but only one can be used on the device at a time (i.e. there might as well be only one PFI).  You would need to have all channels you want to trigger in one task and use one of the PFI lines as the digital start trigger. (i.e. "no" ... having one task on the rising edge and one on the falling edge won't work, one task only per digital trigger)

-gaving

Message Edited by gaving on 06-01-2009 10:09 AM

[preston_johnson]

Yes you can use the fifth channel for the tachometer signal.  This is what it is designed for.  The faster you sample, the more accurate the speed measurement.

The order analysis functions in the Sound and Vibration Assistant perform the "triggering" of analog measurements on the instance of the tach pulses and align the magnitude and phase results with the angular position of the shaft. 

I think the right software add on for your project is the Sound and Vibration Assistant with order analysis.  You can downdload and try it from my earlier link.