I'm starting a new project which will measure both sound (from several IEPE microphones) and vibration (from IEPE accelerometers).
In the past, I would define all of the tasks using a simple analog input voltage, then later use the "Scale Voltage to EU" VI to convert the microphone voltages to dB and the acceleromter voltages to meters per second ^2. This worked fine but I always thought I should be using the special VIs provided in the Sound and Vibration Suite.
With the "Scale Voltage to EU" VI, I was able to let the user input units as meters per second^2 for acceleration as well as, (for sound) the reference of 20 pascals for the dB conversion.
Now I'm trying to take advantage of the "AI Microphone" and "AI Accelerometer" VI's, which look new. The problem I have with these is as follows:
WIth the "AI Microphone" VI, It lets me set the sensitivity in mV/Pascal, which is fine, but there is no scale to reference the pascal in order to get dB out. It seems like it outputs Pascals. I'm not totally opposed to this but now I have a signal of units Pascal instead of volts. Is there any other way to make this dB initially?
With the "AI Accelerometer" VI, I can set the units to meters per second^2 but the only options for senstivity units are mV/g and V/g. So it would confuse the user who wants meters per second^2 as a selection to then have to enter the senstivity of the device in mV/g.
Again, with the old way, I just log all voltages using a normal AI analog input task, and laters use the "Scale Voltage to EU" VI which provides all the units and conversions I would ever need. Do I lose anything in precision or accuracy doing it this way?
Can anyone provide what their method is for channel / task setup measuring sound in dB and vibration in m/s^2? Am I missing something?
The example code for the microphone task seems to output the power spectrum in dB:
As far as the units for the accelerometer, the sensitivity will be in units of a Voltage/g because this is a specification of the sensor.
Thanks for the response, Mark.
I see what you're saying. The AI MIcrophone VI task sets the output to pascals. The 1/n octave VI seems to assume Re 20 uPA because it puts out dB.
Regarding the accelerometers, ours are specified also in volts/m/2^2 and all of our testing results are in m/2^2. No big deal, I'll just have to convert by * 9.81 🙂