some advise pls:)

do i need a special PLC if my input is switching 20 times per second?

Hmm, i have a design about a cotton bud inspection machine..The machine is expecting to inspect 20 pieces per second..I have choosen to use a keyence laser sensor, LV-H100 to detect both heads of the cotton buds..I have also choosen a FX1N mitsubishi PLC to serve this purpose but taking into consideration the fast input switching i am beginning to doubt..

please help

20 times per sond is nothing special.
That translates to an on-off-on-off cycle time of 50 ms. And that require a PLC scan time of approximately 20 ms to be reliably detected.
However, that assumes the on-off periods are evenly distributed.
Sensors for detecting material passing by some time has a very short on-pulse.

Apart from that, 20 cotton buds per seconds sounds very little.
Is it maybe 20 per milli-second ?
If that is the case you need a counter card.

JesperMP said:

However, that assumes the on-off periods are evenly distributed.
Sensors for detecting material passing by some time has a very short on-pulse.

Click to expand...

Hmm, what do you mean with on-off period evenly distributed? Like on for 25 ms & off for 25 ms & this should be applied to all measured items? Would there be problem if the on-off period will be not evenly distributed?

JesperMP said:

Is it maybe 20 per milli-second ?
If that is the case you need a counter card.

Click to expand...

Hmm, 20 per ms would be very much fast..but i wonder what is the counter card you mean?

Jesper,

so, i could use an ordinary PLC for this..i'l go check the scan time for FX1N..

Pls try C235-C245,they are high speed counters in FX1N plc.
the speed is up to 60Khz.



-

theripley said:

Hmm, what do you mean with on-off period evenly distributed? Like on for 25 ms & off for 25 ms & this should be applied to all measured items? Would there be problem if the on-off period will be not evenly distributed?

Click to expand...

Just make certain that the PLC scan is somewhat shorter than the shortest of the on or off part of the pulses.

If it is possible depends on if the PLC program scan including update of the i/o image is short enough, and if the digital input for the sensor is fast enough.
For 20 parts per second even a regular input on a normal small PLC is typically OK.

tnx a lothuge help..