Ladder Hierarchy

Get help and insight.
Post Reply
Lees End
Posts: 2
Joined: Wed Mar 16, 2016 1:39 am
Bot?: No

Ladder Hierarchy

Post by Lees End » Wed Jun 13, 2018 8:36 am

I'm having a problem with the ladder logic since the new firmware update, I'm running firmware 4.1.2 build edf0fe2c
The issue I have is as follows
I have float switches which used to protect my elements using ladder logic i.e. if a process / state was asking the element to come on, and the float switch was not made the heat output would wait for the float switch to be made.
The output now comes on regardless if the float switch is made or not....
I have checked the ladder logic, and all is OK, it seems the hierarchy has changed and the ladder does not take priority anymore?

logic is as follows (simplified) |DIN1 | - |PROC0 | - |OUT0| - (OUT0)
|DIN1| = float s/w. normally open
|PROC0| = Fill and heat, state 2 calls for the output to come on. normally open
|OUT0| = Element output
(OUT0) = Element output

Has anyone else noticed this, or has a work around?



User avatar
Posts: 829
Joined: Thu Jan 05, 2012 2:28 pm
Bot?: No
Location: Texas

Re: Ladder Hierarchy

Post by oakbarn » Wed Jun 13, 2018 6:36 pm

This will work:
issue.png (2.7 KiB) Viewed 199 times
You would not need to be calling for Out 0 to be On in Proc 0. It will come on only if Proc 0 is ASSERTED and DIN 0 is Made. By putting Out 0 in a coil slot, you have lost manual control.

It has not changed. For an Out, Ladder Logic is 2nd to Process State.

From my own notes:

GENERAL WARNING: For Processes and there is a hierarchy for precedence.
1. Ladder Logic takes precedence for a Process. If a Process in the last box in Ladder Logic, it may not be controlled outside of the Ladder Logic manually or be started (spawned) upon a State Exit. Only the Ladder Logic may control it on or off. (Running, Active or Inactive, Killed). You have no control even if the Rung is not filled in.
2. State takes precedence for an Out. An OUT is controlled by a State within a RUNNING Process, you may not manually Kill or Activate it. There is also a hierarchy of Processes. A higher numbered RUNNING Process will control the Out if is called for in the current State if there is a conflict with an earlier RUNNING Process.
Ladder Logic takes 2nd precedence for an Out. If the OUT is the last Coil in a Rung Ladder Logic will control the OUT and Manual Control is not available, even if the conditions are not TRUE.
3. Manual Control is only available if RUNNING Process or Ladder Logic is not controlling.

Post Reply

Who is online

Users browsing this forum: No registered users and 3 guests