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rta53

Need Help With Rslogix Program

6 posts in this topic

I have a control panel that has 20 solenoid valves wired to digital outputs of a Micrologix 1200. What I have to do is open each solenoid valve in sequence for 5 mins. In other words, open Solenoid 1 for 5 mins. then close, open Solenoid 2 for 5 mins then close, etc. This is considered auto mode. This is easy to do. However, I also have to be able to do the following: 1. Be able to go to a manual mode that allows the operator to selectively open any solenoid. This also is not that difficult. I am using a MCR to enable or disable the auto sequence. The outputs to the solenoids are outside the MCR so the operator can turn them on by enabling a bit for each solenoid. (via an HMI button) 2. Be able to disable any solenoid from the auto sequence. For example, if solenoid 4 is disabled then the logic will move from solenoid 3 to solenoid 5. I have tried to do this using the JMP and LBL instructions and it seems like this could work. The problem is that I am using the DN bit of the timer for the previous solenoid to activate the next timer and solenoid. So timer T4:3/DN activates timer T4:4. Then timer T4:5 is looking for the DN bit of timer T4:4. However if I have skipped over the logic for solenoid 4 then timer T4:4 will not time out and therefore T4:5 will not start. What is the simplest solution to this? I have never used sequencers.

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Quick and dirty solution: Use the 'enable' bit as a permissive in the rung that turns on the solenoid to prevent energizing the output. If the solenoid x is disabled, move 1 second into T4:x.PRE If the solenoid x is enabled, move 300 seconds into T4:x.PRE The downside might be that you have a period of 1 second during which no solenoid is energized.

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Sounds like a good solution. The 1 sec delay is not a problem. Thanks!

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....like Steve said but it is legitimate to set a timer preset to zero, in which case the DN bit comes on at the same time as the EN bit of the timer.

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Depending on how the ladder is written, add a branch around the timer done bit that drives the next timer. On it you should have the previous timer done bit and the solenoid disabled bit. When you get the time, try programming it with the sequencer. This seems like a perfect application for it. BTW I hated the first sequencer I programmed and still have to review my notes each time to make a new program. Sid

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Why not simply use a sequencer output instruction. Your first requirement (manual mode) should be easy to handle. #2 should be done by moving a zero into the register that represents the solenoid you want to skip.

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