microsecond time base on micrologix

Hi!

I need to keep track of cycle per revolution down to microseconds on a micrologix 1400. Do anybody know how can I do it?

Appreciate any help.

The 1400 has an HSC function it uses inputs 0-3 (these are isolated from the other inputs you need the manual if possible.
Note: the HSC can count at 20,000 cycles a second.

Rtc?

I don't believe you can. The free running clock coupled with Event Input Interrupt (EII) function file will get you as close as you're going to get but the best resolution you'll get it 100 microseconds. The inputs will also be limiting in that the fastest input filter setting is 12.5 microseconds.
To be honest your requirement is a very tall order. I'm not sure its even doable with a Logix processor but I don't know enough about them to say for sure (someone else will have to chime in).

If the duration of the event is greater than the input filter setting, then the 12uS filter won't hurt you, but will limit the precision to +/- 12 microseconds. The HSC on a 1400 can count at a rate up to 100kHZ which (in theory) would be to a precision of within 10 microseconds.

The PLC scan rate is also going to effect the resolution. You'd probably be better off trying to find a dedicated device that is doing nothing but counting the pulses and have the PLC read it.