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General => Technical support => Topic started by: cch1955 on August 02, 2006, 01:19:13 PM

Title: A PLC counter question
Post by: cch1955 on August 02, 2006, 01:19:13 PM

In using PLC counters to count transitions on a pulse train from a prox and encoder wheel.

I would like to use PLC counter for this, but am concerned I will get multiple counts for low speed (state does not change between scans) and may miss pulses at high speed (frequency faster than scan time) I know HSC can do this but have used up that capacity.

Is there some functionality in the PLC counters tha deals with this? As an alternative I could use the interupt function or a periodic timer with time suited to the pulse train.

Comments? Samples?

thanks

Title: Re:A PLC counter question
Post by: support on August 02, 2006, 11:06:40 PM

Normall counter will not get multiple counts at low speed. The counter will not increment/decrement unless there is a state change in its triggering circuit. However, the total scan time (logic + I/O scan time) will limit how fast the signal may change without losing count. The minimum I/O scan time for T100MD+ is 2ms.

If you need more than 2 high speed counters, consider using two PLCs and they can communicate via RS485 to exchange data.

Title: Re:A PLC counter question
Post by: evanh on August 03, 2006, 02:49:07 AM

http://www.tri-plc.com/yabbse/index.php?board=1;action=display;threadid=764