Ultra Fast rotational Speed meaurement

[deltabravo460@gmail.com]

Hello, I am new to this form and seeking help designing a Tachometer to measure the rotational speed of a turbine, Max speed 450K RPM, I am thinking stroboscope is the way to go. My first thoughts are to use my wave generator (Leader LFG-1310) to drive an LED via an interface circuit. Any thoughts or suggestion?

[Benta]

450k rpm is just 7.5 kHz.
Piece of cake.
Paint 180 degrees of the output shaft black and use a reflective optodetector.
Or mill two slots in the shaft and use an inductive pickup.
Or...

[PCB.Wiz]

This is likely to be small, a possible reflective opto sensor is  NJL5912R at Digikey.  1.06 x 1.46 x 0.5mm

[mjkuwp]

Optical interrupt sensor.  use a rotor with a rotor that only blocks the LED for 1/2 the rotation angle.  These sensors have an LED on one side and a phototransistor on the other.  I don't know exactly if it can do that speed but i would guess so.  You just need to look at the specs. of such parts

[Benta]

use a rotor with a rotor that only blocks the LED for 1/2 the rotation angle.

... and try balancing that mechanically/dynamically.

I think the black coloring is easier.

[Benta]

This is likely to be small, a possible reflective opto sensor is  NJL5912R at Digikey.  1.06 x 1.46 x 0.5mm

Good point. The rpms indicate either an engine turbo, or a small gas turbine. On both, you'll probably need to do the measurement on the shaft end surface of the "cold" side.

[CaptDon]

Could the O.P. elaborate on the turbine? The fastest rotating speeds of any combustion turbine or turbocharger I have ever dealt with was 100K. His turbine is over 4 X faster. It must be microscopically small? Even hydro-dynamic self centering fluid bearings are seldom rated much above 100K RPM. I'd be interested to hear why a turbine needs to spin that fast? Once blade tips exceed the speed of sound the trade offs become huge!! You can hear the buzz-saw sound of aircraft turbines when the fan blade tips are above Mach 1. They don't however remain in this mode at cruise speed.
At 450K RPM even dust impinging on the turbine blades will cause erosion.

[joeqsmith]

https://racespeconline.com/products/turbo-shaft-speed-sensor
https://www.turbomotiv.com/product/garrett-turbocharger-speed-sensor-kit/

Could the O.P. elaborate on the turbine? The fastest rotating speeds of any combustion turbine or turbocharger I have ever dealt with was 100K. His turbine is over 4 X faster. It must be microscopically small? Even hydro-dynamic self centering fluid bearings are seldom rated much above 100K RPM. I'd be interested to hear why a turbine needs to spin that fast? Once blade tips exceed the speed of sound the trade offs become huge!! You can hear the buzz-saw sound of aircraft turbines when the fan blade tips are above Mach 1. They don't however remain in this mode at cruise speed.
At 450K RPM even dust impinging on the turbine blades will cause erosion.

The turbine speed depends on the design and exhaust volume. In small turbochargers, the rotating assembly reaches speeds of up to 300,000 rpm.

https://www.mahle-aftermarket.com/media/local-media-north-america/pdfs-&-thumbnails/catalogs-and-literature/turbochargers/turbo-damage-brochure-mo-2-612.pdf