Reading the RPM from an engine alternator W signal

[240glt]

Hi.

I need to get the engine RPM from an diesel engine, with pure mechanical injection (no engine ECU). There is an alternator with W signal. I have looked at the signal with an oscilloscope, and it looks like the attached photos: -30V to +34V, 167Hz at idle, and 400Hz at 2000rpm. That voltage levels is not quite perfect for the MC024-010 controller that I intended to use.

Have anyone of you made something similar? Do I need to have diodes to limit the voltage levels, or is it enough with just the resistor? I guess that there is diodes in the controller input, maybe that is enough if I use a high resistance (like 100k) to limit the current?

Thanks!

[240glt]

I forgot to attach the schematic of what I hope that I don't need:

[Neil]

Hi.

I have read the W pin as a Straight Freq and Per into controllers without any issues.

regards Neil.

[Jakob]

Hello
The diesel engines I usually work with are using a 24V alternator, and I have also just connected the W signal direct to the MC input.
It has worked without any problems.

What battery voltage is your system running at?


regards Jakob

[240glt]

Thanks, that will make it easier! I was just a little bit worried, as the specification says "Allowed voltage at pin 0-36VDC". And I have negative 30VDC half of the period.

Yes, it's a 24V system.

Thanks!

Regards
Kent