I am currently starting to study vibration of liquid surfaces and need to calibrate the response of Bruel kjaer 4808. Does anyone know how to get the output amplitude/freuquency response against the input voltage and frequency?
The design of the vibrator is ensuring a perfectly proportional response between the driving current and the force generated. If you use the dedicated power amplifier, it comes to a force response strictly proportional to the command voltage. The simplest calibration set-up is to attach a small steel block and a lightweight accelerometer to the shaker, at low frequencies F=M*A so if you measure the weight of your mass and the acceleration per applied volt command to the power amplifier you determine the generated force. Anyway, the calibration is provided by the datasheet of the vibrator and power amplifier, and unlikely to evolve in a normal usage.
You might find that in your case the force is an improper reference, because you might decide that your preferable input reference is the displacement or velocity or acceleration in consideration of the physics underlying your experiment: in that case, you need to include an accelerometer at the shaker interface, but you have to use the accelerometer signal (possibly integrated once or twice for velocity or displacement) as input for the closed loop control of the power amplifier command - checking that you don't get off the maximum performance envelope of the shaker ! (max current, max amplitude). If unsure, get advice from B&K support!
Not completely without the interest of the company I am employed :-) I can recommend a laser vibrometer that can accurately measure vibration amplitudes in a wide range of frequencies (DC up to 2 or 3 digit MHz).
I do not think it is an exiter you have, it is an acceleration recorder.
Connect it to a volt-meter (use an amplifier in between if necessary). Put it the right way up and adjust your volt-meter to zero. Then tilt it over 90 degrees and record the value on the volt-meter. That recording is equal to the gravity constant g at your position on the planet, i.e. approximately 9.81 m/s^2. Turn 180 degrees over, that volt-meter recording is 2xg.
If in doubt, talk to Bruel and Kjaer, their service is usually excellent.
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