mitsubishi high speed counter

M Batty

Guest
M
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. Welded on the shafts is a piece 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 kept 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.

To get by, 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 mitsubishi plc's 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
 
It does sound like it's simply a matter of the PLC not seeing the pulses. You might try increasing the size of that 'piece of metal' on the shafts to lengthen the ON pulse, allowing the PLC enough time to see it.

Note: Your problem may lie in the OFF pulse, so you'd need to do the opposite and decrease the size to lengthen the OFF pulse. Ideally, in you application, the flag should be 180° long, providing an equal ON and OFF time. This will allow the best chance of seeing the pulses.

The only problem I see with your 'ignore' solution would be if the prox. switch failed while at full speed. You might want add a timeout fault if the pulses are not 'refound' within a certain time during slowdown.

beerchug

-Eric
 
HI M BATTY !

CAN YOU USE AN OPTICAL SENSOR WITH SLOTTED WHEEL TO MAKE SURE THAT
PROPER RISING & FALLING EDGES ARE ACHIEVED?
WITH MITSUBISHI FX1N & 2N I HAVE USED C235 & C236 TO COUNT PULSES FROM AN ENCODER OF 360 ppr AT 8 TO 9 rpm ( i.e. 48 cps ) & FOUND IT OK.
AS SUGGESTED BY ERIC THE HYSTERYSIS NATURE OF PROXY SENSING MAY BE THE CULPRIT.
I WORK ON FX PLCS FREQUENTLY SO I WOULD BE INTERESTED IN KNOWING THE EXACT CAUSE OF THE PROBLEM.

REGARDS
ASP
 
program

M Batty
would you please give us a more details about your program,do you have an anlouge output in your system.
I face this problem before with mitsu FX2n communicating with HMI E300. while i was using the high speed inputs with an encoder in a cut to legnth aplication with anloge outputs to inverters to control the Tension in the line.
what i face was that i didn't get the same legnth each time and the variation in legnth was extremly obvious .when i monitored my program i found that the HSC is alawys reset at the same value even though the legnth is not equal.this is was terrable because i know that Mitsu PLC treat the HSC as an interput not depend on the scan time.I tried every thing and all the applicable commands such as the REF command and input filter setting command but alawys i get the same result.
I solve this problem in the following way which i don't know if it's suitabl for you or not.
I purchase the samllest FX0s controller it was 6/4 I/O and used it only for legnth measuring and get an output from it as an input for the FX2n which contain the entire program with analoge output ,sequance,scaling parameters.....etc.
after this i didn't get even 1 mm difference in the legnth.
may be it's not economical but i didn't work except this way.
Good LUck
 
I want to know how make configuration for HSC on Mitsubishi FX1n 24MR - smple program or manual PDF
thanks for your concern
 

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