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OLi

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Reply with quote  #1 

I have finally found a case where I get torsional data from zebra tape and a laser opto tacho and CopTec box.
Signal in the "Torsion plane" TWF looks like a bad supply voltage it is basically a fuzzy sinus but with
a transient jump giving a lot of multiples. In the FFT it is a long multiple of 37.5Hz peaks with a couple
of larger peaks in the middle that still are in the same multiple family or very close.

"Machine" is a combustion engine driven "fan" system with a set of gearbox and tooth belt reduction nearest the fan.
Zebra tape is applied on the fan shaft that have a speed of apprx. 1000RPM.
There are features including straight cardan shafts w/o any offset neither horiz nor vert and a angle gbx with 1:1 ratio and
likely some more features I don't know of. 
I am trying to find a connection so it would match the firing freq. of the motor and/or the blade pass of the fan but neither seem to fit yet but I try to confirm the ratios.

I am for sure not used to look at data in this plane so I get confused on a higher level......
It does not really look like I expected anyway, is it supposed to look like that?

Torsion problems are likely as the torque pin used to transfer force to the fan is eating up the hole it is radially stuck in the shaft and will eventually break.

Is this normal when looking at Torsion data? I maybe would have liked to keep measuring on machines w/o torque issues then....


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John from PA

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Reply with quote  #2 
Quote:
Originally Posted by OLi

"Machine" is a combustion engine driven "fan" system with a set of gearbox and tooth belt reduction nearest the fan.

Zebra tape is applied on the fan shaft that have a speed of apprx. 1000RPM.
There are features including straight cardan shafts w/o any offset neither horiz nor vert and a angle gbx with 1:1 ratio and
likely some more features I don't know of. 
I am trying to find a connection so it would match the firing freq. of the motor and/or the blade pass of the fan but neither seem to fit yet but I try to confirm the ratios.



Between a combustion engine, fan, gearbox, tooth belt reduction, cardan shaft, angle gearbox I too am
Quote:
confused on a higher level....


Can we get a sketch?

Walt Strong

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Reply with quote  #3 
Olov,

I don't think you can rely on the Zebra tape that has a 1x discontinuity for good data quality. I tried this without success, especially looking for order multiples. There are a few technical papers about this issue, but without a practical solution. I have used a printed paper disk with uniform pie elements adhered to front (NDE) of engine with IR optical sensor, and also a magnetic sensor at the flywheel teeth with the Copp-Tek F-V converter. Both gave good data. A separate 1x marker at TDC and sensor is useful for tachometer speed, phase reference, and waveform processing.

Walt
OLi

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Reply with quote  #4 

Yes I have a tacho speed sensor also and problem is not order multiples so far, rather lack of....

Think of a device in terms of looking like a helicopter and this is the tail rotor......


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John from PA

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Reply with quote  #5 
Quote:
Originally Posted by Walt Strong
Olov,

I don't think you can rely on the Zebra tape that has a 1x discontinuity for good data quality. I tried this without success, especially looking for order multiples. There are a few technical papers about this issue, but without a practical solution. I have used a printed paper disk with uniform pie elements adhered to front (NDE) of engine with IR optical sensor, and also a magnetic sensor at the flywheel teeth with the Copp-Tek F-V converter. Both gave good data. A separate 1x marker at TDC and sensor is useful for tachometer speed, phase reference, and waveform processing.

Walt


I have frequently used a Hall effect speed sensor mounted to observe the flywheel ring gear to pick up torsional activity.  My experience is such if you are adding such a device, one with a rectangular pole piece works best.  The active type also works better than the passive type because of the constant voltage output.

There is very often such a device already mounted on the engine and utilized as part of the engine controls.  On a few occasions, I have tapped into that signal and utilized it for a torsional study.    
OLi

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Reply with quote  #6 
Problem here is not primarily in the motor end but in tail end....
I have only access to a very small part of a small shaft.

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OLi

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Reply with quote  #7 
Changed to a basically thicker shaft and signal changed significant, much lower, not the same multiple pattern, "jump" in TWF is much softer so maybe it actually works. IRL testing will verify.
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Walt Strong

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Reply with quote  #8 
Changed to a basically thicker shaft and signal changed significant, much lower, not the same multiple pattern, "jump" in TWF is much softer so maybe it actually works. This would be an interesting outcome, if the same installed Zebra tape was used for the second set of measurements. If the Zebra tape was changed when the shaft was changed, then perhaps the some or all of the signal improvement was due to the change in Zebra tape installation.

Walt
OLi

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Reply with quote  #9 
Well frequency content change with speed, we have full speed and idle. It also (mostly "amplitude") vary by load by change in vane angle. Tape may be applied to the same collar but I have to verify. It will also be verified by 100+ hour running that with old shaft generated visible damage. So in a couple of weeks we will know about that unless damage will show earlier.
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