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How to Measure Phase of Signals

How to Measure Phase of Signals

How to Measure Phase of Signals

(OP)
I am trying to measure the phase difference between three signals.

The signals are given mathematically by the equations:
X = sin(2w) - cos(w)
Y = -sin(-2w) - cos(w)
Z = cos(2w) - cos(-w)

where w = 1800Hz

The 3 double frequnecy components are 120 +/- 12 degrees apart. The single frequency components are 0 +/- 5 degrees apart.

Mathematically the easiest thing to do (i.e. for phase between X & Y) would be to be use the MATH function on the scope and add a cos(w) to X & Y, however, the problem is (I believe) there is a phase shift between the cos(w) of the measured signal and the input cosine signal and so the components do not cancel each other out completely. (I do not have acces to the individual signals components on the module). When I simulate the signals myself, it works out great, becasue I am using the same cosine signal at the same phase shift, however, in my reality, I cannot get this to work.

Are there any suggestions on methods (or equipment) I can use to perform this measurement? I have also tried a NAII Phase Angle Voltmeter model 227 and either I did something wrong or it will not make the measurement either.

I would prefer to do this in either software (Labview or C) or with test equipment, preferably test equipment. I do not want to add hardware to my test fixture at this point.
Thanks in advance for any input. My deadline is looming...

RE: How to Measure Phase of Signals

First, you have to decide what components you want to measure phase angle between. Hint: there are four frequencies. This can't be a real world problem. It sounds a lot like a trick question asked by a professor.

Are you sure this isn't a student posting?

RE: How to Measure Phase of Signals

(OP)
Sorry, but it is a real world problem.

I am writing a test for an electronic module according to a test specification I was given.

The signals are for a gyro with an XYZ coordinate system. There are several different stages that have only one harmonic, but there are 2 stages where there are 2 harmonics.

All I care about are the phases between the second harmonic signals which are 120 degrees apart. However, if I can figure out how to measure those, then I can also measure the fundamental frequency phases as well (which are 0 degrees).

RE: How to Measure Phase of Signals

Why you can't subtract Y from X?

TTFN

RE: How to Measure Phase of Signals

(OP)
I can't subtract them because I need a point of reference. I can subtract them and get a nice sinusoid that is rotating at 3600Hz, but I have no way to determine the phase shift that occured when the waves were subtracted.

Thanks for the suggestions though, it is a good one. I tried that first. ;)

RE: How to Measure Phase of Signals

It sounds like a redundant exercise. With a gyroscope what you are measuring is the current induced in the opposing windings due to the precession of the gimbal. Then it is simple math.

RE: How to Measure Phase of Signals

(OP)
RSBUCK,

Sounds like you know about navigation systems. I am only writing the test for the gyro toquer module in the system and am testing the precession stages later on, but these signals I am having issues with are the damped, torqued signals.

I guess I will end up digitizing the signals and doing math on the data. That's the only sure fire way I know to make this measurement, I just find it hard to believe that one of the many test instruments I have to play with won't do this automatically or with a little scope MATH.

RE: How to Measure Phase of Signals

Sorry for not understanding your needs. Couldn't think of any way to compare phases between composite signals. If a LabView daq and system is within reach, I think that it should be able to do what you want with "a little scope math".

RE: How to Measure Phase of Signals

Many digital now have a FFT built in or have signal analysis software for processing captured data on a PC.  I would think that a FFT phase-magnitude plot could be used to determine the relative phases of the signal components.

RE: How to Measure Phase of Signals

Silly me...or silly OLD me...I read the first post and immediately thought "Get out your Oscilloscope".  I guess I've been doing this too long.

I remain,
The old (and feeling older by the minute) Soldering Gunslinger

RE: How to Measure Phase of Signals

(OP)
Thanks for all the input.

It looks like digitizing the signals with the scope to get the data and then attack it with the math is the best thing going.

NAII says they have some new equipment that will do it. I bet it will...for a price$$$.


Thanks again.

RE: How to Measure Phase of Signals

IIRC you multiply to detect phase.

Google phase locked loop or phase detector.

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