Tacho' question

[olmod]

Im wondering if a 30 meg frequency counter can be adapted and used as a tacho' as part of a test bed for brushless outrunner motors, i just happen to have a couple :)

[Bruce Abbott]

You will need a tacho probe, which could use an optical or magnetic sensor. Here's an example of an optical pickup:-

MPX Tacho Probe V1.0 (http://www.sea-gull.demon.co.uk/MPX%20Tacho%20Probe%20v1%200.pdf)

The frequncy displayed will be lower than the rpm by a factor of 30, if the sensor sees 2 pulses per rotation, eg. 5000rpm = 167Hz. To get good accuracy the counter should be set to a gate time of 1 second or longer.

[olmod]

Thanks bruce,its good to make use of old gear ,lol by the way i have tried to get in touch with you by email and private messages in the last 3 weeks with no response ??? :confused:

[vintage1]

I would add a bit of low pass filtering to that. Something like a soft 4th order 2kHz low pass.

That can stop noise giving spurious high RPM counts.

[olmod]

thanx vintage 1 ill have to have a talk with a fellow modeller who is very experienced in electronic eng' who may be able to help with the additions that you suggest ,im pretty much a nut and bolt man who many years ago did an ac dc ticket. ;)