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Angular measurements



I am new to Labview (Full) and Sound and vibration measurement suite and wish to know, how exactly should I go about processing Acceleration vs Crank angle degree measurements.

I acquire data through the accels/cam signal and a crank sensor. The crank sensor has (60-2) teeth, and the cam sensor has 1 pulse every 2 rotations (runs half of the speed of the crank). I measure accelerations on the components on the same DAQ, and wish to use the capabilities of the available tools to get Acceleration vs Crank angle. Can someone sort of guide me how should I go about achieving this?


I can also use an encoder (3600pulses per rev)- it would be helpful if something can serve both pupose Crank angle and encoder? (Not sure if this is possible- again I am new to angle domain processing)


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Message 1 of 6

It depends. 


One convenient way, provided your DAQ device supports the capability, is to use the encoder as a sample clock. With the 3600 pulses/rev encoder you would get 10 samples per degree of crank angle. Sample the crank and cam sensors as well as the accelerometers so that all the data can be "synchronized." I use "synchronized" in quotes because you are now working in the angle domain and not the time domain implied by that word.


Now the depends part: If you will be doing signal processing such as filterings, spectral analysis, integration to get velocity or position, you need to be very careful about the mathematics and units. Most analyses are based on the assumption that the data samples are uniformly spaced in time. This is no longer a valid assumption in the angle domain. Some things are fine if you change delta time to delta angle. Filters tend to be more difficult to interpret.  Integration will be with respect to angel and not time.


The other option is to sample at fixed time intervals and fast enough to capture the encoder signal with the desired angle resolution at the highest speed. Then recalculate (or select) any values you want in the angle domain at the appropriate times. 


Which is the more appropriate approach depends on what kinds of analyses you want to do and what kind of DAQ hardware you have.



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Message 2 of 6

I am looking for is Y (data-can be acceleration/strain etc) vs Crank angle degrees. I am not going integrate to achieve velocity or position (I understand that is better to be done with time domain data). I am looking to sample it at fixed time intervals with an angular resolution of 0.1deg~1deg. I have a C-Daq-9178 and three NI 9234 (BNC-Analog input modules for acceleration/cam) with Labview and Sound and vibration measurement suite.
I am concerned how would I acquire the Crank angle degrees part for the x-axis-with having the cam signal (pulse voltage) and the encoder.. (I can arrange for a Digital input module-9204 if this task cannot be achieved through an Analog Input 9234 module)
(I do have a timing diagram of the engine-do we need it?)



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Message 3 of 6

Anyone willing to help me out over here?
I am looking at this example to try to use it. But I am not sure about the Z index initial angle and the Z index phase that I can find out. The Z index may not exactly be at the TDC of the engine.

Tips? More examples that can make this easier?

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Message 4 of 6
In the past, I have worked on an application that sounds similar, but our encoder only had 360 pulses per rotation, in addition to the 1 pulse per rotation output.

When installing the system ensuring that the 1/rotation pulse occurred at TDC of a particular cylinder was part the alignment process.

In the software we use the pulses in two ways. First the 1/rotation served as the DAQ trigger and the 360/rotation was the DAQ clock. This allowed us to measure cylinder pressures relative to crank angle -- which was what was really important.
Second, using a counter card we also measured the time between consecutive pulses. Those counts, and a little basic math, allowed us to measure the instanateous rotational speed of the crankshaft.


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Message 5 of 6

This is exactly what I am trying to do Mike.


I would like to do this eliminating the alignment of TDC with the 1/rotation pulse (Since I don't have the equipment to monitor this)

Can I do with or without the alignment on Sound and vibration assistant?

Do you hav example Labview codes that can help me acheive this?


In short, some guidance which I can make sure that it will work.


Thanks in advance


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Message 6 of 6