Cheap Turbocharger RPM measurement

Acoustic? Somehow I don't think so... But it would be interesting so see if you could sample an Ultrasonic transducer fast enough to get a decent RPM x number of vanes signal... It would certainly be cheap.

Al...

Building on Al 's thought: if a tube could be inserted in the compressor wall so as to sample the fan vanes, a passive piezo sounder could be rigged as a sensor, which might well provide a vane pulse with minimal, even no amplification. A divide stage, then an electronic tacho would complete the rig. Cheap

Brian Whatcott Altus OK

I'd start by bonding something (maybe a pizo sounder.. but I think I'd go looking for a small Ultrasonic pizo element) to a spot on the compressor case (it'll be cooler there than on the exhaust side) that is close to where the vanes whip past a port edge.. (intake port ;-) I bet you'd get a signal there. Would it be clean?.. Be worth a try.

If the turbo on my VW Van wasn't so hard to get to (find even 8-) and if I had a scope that sampled fast enough, I'd give it a try myself.

Al...

Assume a 150,000 rpm top speed, and 12 blades...

The signal frequency will be 30 K Hz and the sensor must therefore have a higher switching frequency.

Inductive sensors normally have a switching frequency of 1 - 5 kHz, though

Capacitives tend to be about 100 Hz

Optical sensors typicaly 1 kHz or less.

Ultrasonic sensors only 1 to 5 Hz

I think you will have a problem with finding any sensor that will work.

It might be interesting to see if you could pick up vibrations from the blade with some sort of microphone, but a clean signal would be unlikely.

-- Jonathan

Barnes's theorem; for every foolproof device there is a fool greater than the proof.

To reply remove AT

Slight niggle, an ultrasonic microphone can easily measure to 100 kHz. I think you are referring to a complete sender/sensor unit as used for distance detection, which has a much lower performance. I think this is your best chance of a cheap system. Pull the mic out of a parking 'radar' kit. The one I have here is made by Velleman and works at 40 kHz.

There is no reason in principle why an optical sensor can't be used, if you have access to the shaft of the turbo. Paint the shaft black, and then paint a white stripe on it. RS Components in the UK used to sell a nice little slotted disc with an optical encoder which I used to measure the speed variations of a turbo.

Cheers

Greg Locock

I know a guy who did it with an photodiode and an oscilloscope. I do not recall how he triggered the photodiode, but it was pointed at the shaft of the turbocharger. He did comment on the time it took the diode to turn on and off. And about the pilot-this was in an airplane-paying more attention to what he was doing than flying the plane.

John

All of these suggestions - how to they hold up to intense heat?

Dave

You don't _have_ to measure the _hot_ end.

-Mike-