transient strain gage measurement

[ampalumbo]

I have some questions regarding an experiment I'm designing for my university's stress lab.  I have a strain gage connected to a small cantilever beam.  The goal of the experiment is to drop a golf ball on the end of the beam and record the oscillations in the strain.  I am using an NI-9219 to connect the strain gage to the laptop.

I'm wondering if the DAQ can have a high enough sampling rate in order to accurately capture the strain results vs. time.  I also need to find a way to perform an FFT on the data, in order to perform a vibrational analysis.  I will be checking back here periodically in case I need to give more information in order for someone to accurately answer my question.

Thanks in advance,

Adam

[RavensFan]

Your 9219 only has a sampling rate of 100 samples per second per channel.  That doesn't seem very high.  That means if you acquire data and run an FFT on it, you'll only be able to detect up to 50 Hz vibrations.  It depends on the geometry and dynamics of your cantilevered beam system, but it just some seem to be to be fast enough for what you are trying to do.  Do you have an idea of what frequency of oscillations you expect?

Check out this link.  http://digital.ni.com/public.nsf/allkb/3F3165FE0709B8B38625733E007D7C55

[ampalumbo]

I may make the experiment simpler.  I have a Vishay P-3500 Strain Indicator, and I would like to hook it into the DAQ and design a VI to mimic an oscilloscope.  I also have access to an NI 9264, which I believe has a sampling rate of 25,000 samples/sec per channel.  The purpose of this experiment would be to find the peak voltage when a golf ball is dropped on the beam, and the equivalent static load can be found.

To answer your question about the frequency of oscillations, I performed a similar experiment using PULSE.  When measuring the vibrations with an accelerometer, the frequency span was set to 3.2 kHz.  When the FFT analysis was performed, and span setting was adjusted to 500 Hz.

The simpler experiment may have to be used.  However, with the NI 9264's higher sampling rate, I think it may be sufficient to use for a proper vibrational analysis.  I just need to know a way to connect the P-3500 Strain Indicator to the NI 9264, and what type of data I am actually recording/performing an FFT.  (BTW, the strain indicator has just a single analog output: P-3500)

[RavensFan]

The P-3500 has an analog output of +/- 2.5V.  It has a BNC connector on it.  You just need to wire a BNC cable from that to an analog input DAQ module.

The NI-9264 will not work.  It is an analog output module.  You need to use an analog input module.

[ampalumbo]

My apologies.  I should have said an NI 9237, which has a sampling rate of 50 kS/s per channel.

[RavensFan]

The NI-9237 is a bridge based module, either half or full bridge.  So you won't be able to use the Vishay P-3500 at the same time.

Does your sample have a single gage on it, or is it set up as a half or full bridge?

[ampalumbo]

It has only a single gage.

[ampalumbo]

It appears that I am able to use my NI-9237.  But it is only compatible with a quarter bridge strain gage setup if I connect it to an NI9944/9945 Quarter Bridge Completion Accessory, which I will be purchasing shortly.

Thanks for your responses.