Prox switches and HSC

[Guest Mike Batty]

Hi, I wonder if any of you could help me I recently did a refurbishment of a machine. The machine had an old and dead PLC and I replaced it with a Mitsubishi FX1N 60 MR. The machine has 2 drums that spin at high speed. Fastened on the shafts is a peice of metal that a proxy looks at each revolution. In the old system - the signals from the proxys went to 2 special cards (neither have worked for a long while) which changed a relay state and told the old plc that the drums were spinning. I wired these proxys straight to X0 & X1 and used high speed counters C235 & C236 to monitor them. (I was using DMOV and DCMP every second to prove the drums were spinning) However, I keep getting a fault that the drums (one of them) is not spinning. I programmed the machine to lock out and brake the machine if this happened. When I monitor the program, I see just sometimes that one of the proxys fails to register any counts when it gets to a certain speed. (about 26 pulses per second) the 26 pulses per seconds is full speed and it holds this speed for about 10 mins. For now I have proved rotation by allowing the counts to be measured until full speed is acheived, then not allowing the 'missing counts' signal to lock out the machine. It seems safe enough???? as the machine slows down, the counts are refound and it is monitored to a standstill again. But I would like to keep check on the counts all through the cycle. I did think that mitsu could handle more than 26 cps (or 52 really with both HS counters) or is it that I cant use proxys for this kind of measurment

[Sergei Troizky 26]

First, swap the inputs for the sensors and test. Probably, the problem is the sensor itself. By the way, for rotation confirmation only you do not need a HSC. Just read the pulse catch bit and reset it right there. No signal for certain time= no rotation.