I would use proximity probes if you are primarily going to measure
vibration.
They are also the best choice if you are going to notch the shaft and do
phase measurment.
I'm not sure about other venders' prox probes, but the one's I'm used to
have a linear range.
The phase measurment can be gained so that it rails one way when over the
notch and rails the other way when not, so you don't have to worry about the
linear range. As for vibration measurments, you will have to make sure that
you stay in the linear range of the probe.

I want to make sure I understand what you meant by having a filter at the
resonance points.
Are you only going to measure vibration at resonance (i.e. bandpass)?
Or, are you NOT going to measure at resonance (i.e. notch filter)?
Keep in mind other events may cause vibration, such as impulse, rub, etc,
which will likely occur synchronous to the shaft, and have nothing to do
with resonance.
This is where a phase reference may be handy because you could determine if
it is happening 1X/rev, 2X/rev, etc.
OR, are you assuming that an impulse/rub event will excite the case at the
resonance frequency?

At any rate, what you intend on doing is definitely do-able.
I recommend playing with probes a bit to see what you get.
Sounds like a fun project.
Let me know if there's anything I can offer...

Adam


"RST Engineering" wrote in message
...
Proximity probes? Or accelerometers?

I understand about the analog circuitry and actually plan on making a five
or six channel filter at each of the possible resonance points relative to
the fundamental ... and then strobing the filters to light a "normal",
"low", "high" lamp for each channel.

Jim




As is tradition, we tend to get off topic ;-)
I think you can accomplish this using the methods discussed.
Mount 2 proximity probes 90 degrees apart.
Calibrate the readings for normal low vibrations (be sure to account for
any nonlinearities in the probe).
Design the circuit to trip the buzzer/lamp when the vibration exceeds the
normal level.
You may need some analog circuitry to help (gain, etc).
But you don't need to get much fancier than that.

Adam