How to calculate frequency from counting pulses measurement

Many times is necessary to measure frequency in industrial automation.

Normally it is done from a pulses generator signal. The S7-200 CPUs have high speed counters incorporated to do this task. The conversion counting pulses to frequency, however, must be done by user software.

Despites it is a not complicated evaluation, many users of S7-200 have difficult to implement it. Think in this case, I program an easy subroutine to do this calculation and a little text about theory and pratical implementation.

Hi Mr. Pegaia,

Your interesting routineput me doubts about a program Ijust implement.Let me describe the case:

I´m in a projectwere I need to implement speed sinchro of two motors.
I implement two speed measurementsusing HSC´s with Time Interrupt 0 and 1 to garantee my speed measurement.
I could not find interrupt implementation on your routine.
Now I can make you a question:

Without an interrupt to precise measure time,can we garantee speed/frequency values?

Count with your understanding, both my english and CLP knowledgement are still poor.
peharps we can talk in portuguese for a clear conversation.
Best regards,
André
Recife-Pernambuco-Brazil

I have tested this code using a proximity switch. One pulse /rev.

The rpm value is unstable; it jumps up and down with up 100 rpm @ 2100 rpm despite constant rpm of my test motor.

I think an interrupt is a must to track time properly, maybe there is something to do in “System Block”. I tried to change Input Filter to 0.8 ms but could see no changes

Is there anyone out there that have some code to share?