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Posted
Hello, Trying to learn to use the FM350-1 counter module. Have an SEW incremental encoder (5V, 1024 ppr) that I spin between my finger and thumb. Encoder is set up correctly and works well, can see the pulses being counted and no fault LED on the FM350 module. Goal is this: Load (M20.3 Load Direct) 0 into DB1.DBD34 Spin the encoder. Compare the actual encoder (counter) value against 1024 When actual counter value = 1024, load 0 back into DB1.DBD34 i.e. reset it to zero. With reference to the code in the pictures below, what I have noticed is this: When I spin the encoder 'quickly' for slightly further than one revolution the counter value does not reset to zero when exactly 1024 pulses have been counted, it can count as high as 1200 or more before the count is reset to zero if the encoder is spun really quickly. It's probably because I'm not using the card interface properly. Reading the FM350 PDF leaves me a bit flummoxed. Any ideas about what I'm doing wrong? Any advice greatly appreciated and thanks in advance for it.
Posted
The FM350 count without missing any pulse. Your plc read request the count to the FM350 card and then the card return the count, like a snapshot. The plc scan time can affect the response time, i.e. if you turn the saft at 10 turn per second, you got 10240 pulse per second. If the plc scan is 5msec you can lose 51 pulse between each count reading (0.005sec * 10240). This is why the error is greather when you increase the speed. For get a quick response, you may use the output on the FM350 itself, these output are not affected by the scan time of your plc.

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