Turbo RPM sensing. Discuss.

I just bought the rpm datalogger setup yesterday and need the ability to monitor shaft speed. I'm not wanting to remove any material from the turbine shaft, however modifying the cover to mount a sensor would be easy enough. I think I'm going to try the BW sensor since it seems to be the cheapest option and should be of decent quality. Randy was not aware of it, however he has made the Garrett one work in the past. I don't think you can buy the Garrett sensor alone though?
 
Something to consider:

If you're counting every blade and the sensor is missing one blade per revolution, you're off by roughly 9% on an 11 blade wheel; or 4.5% if you miss a blade every other revolution. You would possibly miss that on a log.

When you're looking at one count per revolution, you would see a dramatic decrease in turbine speed. It would be painfully obvious in the log.

I didn't like the idea of notching the shaft. However in the turbos that I've had fail, they failed in areas other than where the machine work was done. It hasn't posed a problem in my applications.
 
I don't like the notch in the shaft either but it is routinely done with tractors and they push turbos just as hard as anyone in pulling.

The accuracy question....1x per rev is a lot easier to "see" with lower speed/simpler electronics. 100krpm = 1667 pulses per second. No biggie. Take that x8 for blade count (for example). Neither are really all that fast in the chip world but you get the point.
 
Sensing the compressor wheel some distance from the shaft can become problematic. Simple terms the target being very small and traveling too fast.

Given the choice I'd always read off the shaft for the most stable signal but it isn't likely the best option as an afterthought add-on.
 
Joesixpack said:
Sensing the compressor wheel some distance from the shaft can become problematic. Simple terms the target being very small and traveling too fast.

Given the choice I'd always read off the shaft for the most stable signal but it isn't likely the best option as an afterthought add-on.
Click to expand...

Agreed but any high end turbo shop can do the notch and sensor install for a few hundo.

While some OEMs will sell you the blade-sensing style as an aftermarket accessory, all the VGTs I have seen are shaft-style from the factory. Hmmm....
 
Cummins uses a EDDY current senor on the shaft.

I don’t image that an inductive pick up style sensor would work well with a cast wheel, without knowing the composition I can’t imagine they are blending in a ferrous metal during the casting process.
 
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