New to measuring vibration, hoping for input

[deskpilot]

I have never tried to measure vibration before, but now have a requirement for it. I will be measuring two accelerometers with a 9201 in a CDAQ chassis. Hoping to take measurements at around 1 kHz. I do not have the sound and vibration toolkit.

The only thing I know about the system is the limits. I have one set of limits in mils, and another in inches/second. I have decided that the inches/second limit must be the double integral of the accelerometer multiplied by the frequency of the acceleration signal. The in/sec limits are about 1000 times the displacement limit, so I may have to sample a little faster.

I also have specs on the accelerometer. Nominal sensitivity is listed at 120 Hz and the frequency response is listed as +/- 5% from .5 Hz to 2800 Hz.

I'm thinking of doing the following to try to get rid of drift that I have read about in other posts: Use the extract tone information on the accelerometer signal to get frequency and amplitude. Wire this to a function generator that creates a sine wave from the frequency and amplitude. Then double integrate that, use the Extract Tone again to get amplitude of this, and multiply this by the original frequency of the accelerometer signal. Sound reasonable, or should I stick to operating on the original signal?

Any other suggestions for tackling this project? I need the algorithm to work reasonably well the first time we run this, and then hopefully I can go back and tweak the code based on what I see from the first data set.

[preston_johnson]

the 9201 is only a 12bit ADC and may not have enough resolution for the lower level vibrations from your accelerometer.  have you connected the accelerometer to your system yet?  Do you have a power supply for the accelerometer?

An alternative is a 24 bit Delta Sigma ADC with built in anti-aliasing filters which are commonly used in vibration measurements.  The 9234 also supplies power to common piezoelectric accelerometers (IEPE) such as the ICP accelerometers from PCB. 

What is your unit under test?

For integration, there are a couple of key steps and the math is understandable, yet tricky to implement.  The Sound and Vibration Toolkit and the Sound and Vibration Measurment suite are well suited for vibration measurements including integration to velocity of the Time Waveform.  https://www.ni.com/en-us/shop/product/labview-sound-and-vibration-toolkit.html  There is evan a out of the box assistant, base on NI Signal Express, that has these functions and can help you get up and running quickly. 

Hope this helps you get started:

Preston Johnson

Vibration Analyst II (www.vibinst.org)