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General => Technical support => Topic started by: kparson on December 13, 2011, 07:29:29 AM

Title: Counting Pulses on PMON input
Post by: kparson on December 13, 2011, 07:29:29 AM

 I would like to count the pulses arriving at input #4 on a T100MD.  This pin is defined as a pulse measurement pin.  Can I also use it to increment a counter?  If using a regular counter can I expect it to accurately pick up a 30Hz signal?  Program size is about 2000 words.

Title: Re:Counting Pulses on PMON input
Post by: support on December 13, 2011, 08:44:04 AM

For regular counter it will depend on how much time your program spent per scan. If there are complex custom function that communicate with other devices then it may spend longer time than the period of the pulse and you can lose count.

So it is better to either use the HSC (wire to input #5) to count pulses, or define an interrupt input and use interrupt service routine to increment the counter.

If you use an FMD or Nano-10 PLC then an input that is defined as HSC is also simultaneously capture PMON information (i.e. it acts as both HSC and PM). But this is not possible on T100MD PLC.