I have bought a new £26 optical rev counter and would like to check the accuracy of it at high rpm and how can it be checked in a home workshop.

My mechanical counter reads 2850rpm
On a quality 25,000-rpm motor minimum optical reading was 30,000 over 5,000 revs out.

An article that I read on speed testing of electric motors says a strobe should be used?
I require to check a speed range around 70,000 rpm the optical goes up to 99,000rpm.

A visual slow  speed test was done on my lathe i.e. Slowest back gear was selected and a mark placed on the chuck backplate then rpm counted against a stopwatch for a minute.

The lathe speed plate says 50rpm, my stopwatch test gave just over 62rpm, the optical rev counter read 62.4rpm and a mechanical rev counter said 60rpm

My mechanical counter only goes to 20,000rpm.

At slow speeds the optical counter is reasonably accurate but when the revs go above about 2000rpm there are large discrepancies compared to the mechanical counter.

Any suggestions or are these lower priced optical rev counters unreliable at high speeds.

Windy

Edited By Windy on 22/02/2010 17:00:45

Edited By Windy on 22/02/2010 17:01:53

Edited By Windy on 22/02/2010 17:05:24

Edited By Windy on 22/02/2010 17:11:16

Thanks all for your comments it seems the cheap optical one comes out tops.

Have tried reflective tape, white paint and black tape on a bright background as suggested, the readings on the 2800rpm motor where all very close to 3000rpm.

Will borrow my mates old ignition strobe and do a comparison.

Edited By Windy on 22/02/2010 23:58:27

Edited By David Clark 1 on 23/02/2010 10:51:43