I intend to purchase a 4ch scope (2405A) which would be used to measure vibration from rotating machinery. My question is regarding triggering the data collection. I need to make a decision regarding how I measure the speed of a rotating shaft and also obtain a phase relationship between the measured vibrations.
I would plan to use channels 2,3 & 4 to measure vibration using accelerometers. The decision I have to make is regarding what signal I can use in CH 1 to trigger the data collection. I can provide a once-per-revolution pulse signal using a displacement probe close to a shaft protrusion such as a screw. I assume this would work but the problem is the cost of this setup is high for a 'hobby'. An alternative is to use an inductive switch sensor which apparently produces a TTL signal.
My first question is very specific and is - "could the TTL signal be used to obtain shaft speed and to provide a phase reference between the vibration signals?"
My second question is more general and is - "how easy would it be to obtain a shaft speed measurement and relative phase measurement between the signals in channels 2, 3 & 4 if a suitable trigger signal could be supplied to channel 1?"
If you download the software and run it in demo mode you can see the basic features.
In the bottom right of the display are the phase rulers, green circle, which can be pulled onto the trace to indicate the start and end of a full cycle. In the bottom left are the time rulers, white square, which can be pulled on to the trace to see the phase relationship between any point on the screen and the phase rulers.
You can set set up a maths channel to calculate the frequency of a signal and convert this into revolutions per second/minute etc drawing the resultant trace on the screen.
Thanks very much for your response. I have since purchased the 2405A scope.
I am still a bit confused about the phase measurement. In demo mode I can trigger of channel A or channel B and this will freeze the signal and I can use the phase or time rulers.
However my requirement is to measure the relative phase of the signals between channels (eg between channels A & B). When I trigger off channel A the channel A signal is stable and does not move (as one would expect). However the signal in channel B is not stable and therefore it does not seem possible to measure the phase between these signals?
Could you please advise if it is possible to measure the phase between two signals on any of the four channels assuming, of course, the signals to be sine waves and of the same frequency?
Another issue I have is that I thought I would get a software development kit (SDK) with this scope but it appears tht this is not the case - could you please confirm?
although you have to take the value after the phase settles down as the start conditions are unknown and the first part of the trace will be inaccurate.
I take it there is no way, other than using your formula, to measure the relative phase from two channels? So I can't use the phase rulers in some fashion?