AB MicroLogix 1500 PLS function

Shawn Cassidy

Member
Join Date
Mar 2004
Location
Montreal
Posts
98
I'm programming a ML1500 LRP to run a neck banding machine and I've run into a few problems using the PLS function. I'll briefly explain the function of the machine. I have five outputs that come on and off during a cycle of the machine. I'm using an internal pulse output PTO set at 360 pulses per cycle from the plc O:0/2. I then go back into input I:0/0 of the plc to count the pulses with HSC 0. My first output needs to come on when I have 20 pulses and stays on until I have 200 it then goes off for the rest of the cycle. The second comes on at 80 and stays on until 300.... and so on. More than one output can be on at any given time. I can do this using the LIM function (test HSC.ACC) to turn on and off the outputs but I would like to use the PLS function to reduce errors due to scan time. My problem is the set-up of the function. I've followed the explaination from the Knowledgebase notes but I still can't get results. I set-up the HSC0 as instructed but I'm confused about how the mask is working for the outputs. I've added a new data file for the PLS9 with 5 elements.
The outputs I want to activate are O:0/3 to /7.
I set-up the HSC to activate at start and begin counting. Which it's doing. What seems to happening is the HSC counts the amount of pulses for my first output (to 200) then it resets and starts to count the amount of pulses for my next output. It should be turning the outputs on and off while looking at the total count 360 rather than for each individual high count.
I set the OMB in the HSC0 to 248 DEC to mask the outputs but they are also not coming on. Is this function capable of what I need it to do? What interger file is related to HSC0? In the tech notes they show N7:48 as the OMB (output mask bits). Can't I write it directly to the HSC function file?
I just need it to function like a cam switch with 5 outputs. I think I'm just missing a small detail that isn't popping out at me. If anyone has any ideas it would be much appreciated. :rolleyes:
 
Hi Shawn, the problem with Micrologix PLS is that you have to translate your intervals into Output Mask, which makes PLS hard to use even for simple application like this. I had the same problem, and I solved it writing some code which does this translation. In your case, you have Output 1 which is on from 20 to 200 and Output 2 from 80 to 300.
Then this will be the PLS configuration:
Limit Out_1 Out_2
20 1 0
80 1 1
200 0 1
300 0 0
Of course this code must be run everytime you change the cams.
I hope it was useful !

Bye
 

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