Control Logix "Go to Run" Conditions

dbh6 · Feb 28, 2013

Hey guys,

So im currently programming a sequences for my pump logic for a project. I have tested the program and so far its "full proof"

. However i am aware of the infamous "Go to Run" Conditions (courtesy to Ron Beaufort) such that if the PLC's losses its power, if some operator, switch the mode of the plc from run to remote, or from run to program then run, etc.

So i currently have a 1756-L62 5562 control logix plc which iam testing this on, and im trying all possible scenario's. so let me know what you guys think of other ways to test the "Go To Run" conditions.

dmargineau · Feb 28, 2013

There are only two ways to command the CPU to "Go To Run".
One is via controller Mode Key switch (turn to Run or Remote Run positions).
The second is via Online RSL5K software, presuming that the CPU Mode Key switch is in the Remote Run position and the software commanded the last switch from Run mode.
There isn't much testing to be done unless trying to Emulate the application prior to "turning it loose" on the controller.
You will eventually have to run your "fool proof" application on a CPU...What could possibly go wrong?!...

Try isolating the output's power supply and monitor the "running" logic without "making decisions" in the field.

dbh6 · Feb 28, 2013

@ dmargineau, will try out what you insisted.

jkerekes · Feb 28, 2013

The RSLogix 5000 also has a "Test Mode". This will run the logic, but the actual outputs are disabled.

dmargineau · Feb 28, 2013

It was only a suggestion after all...

Complex applications might need to be "emulated" prior to CPU deployment.
For a simple application (I presume it's the Cooling Tower), once the I/O has been thoroughly identified and verified against the programming logic and if the developer is acutely aware of the consequences of any "malfunction" just a "Test Mode/outputs off" monitoring might be sufficient.

dbh6 · Feb 28, 2013

@ Jkerekes the test mode is pretty useful when testing prior to using your actual outputs, my plc that i'm currently using has a bad battery so if i remove power to the plc while the plc is running and then put power back on it loses its program. The reason why im mentioning this is because i'm trying to simulate what would happen if a power loss occured while the plc was running and what would result if power resumed, im assuming that would be treated as a Go to Run condition, but i could be wrong, let me know what you guys think.

dmargineau · Feb 28, 2013

If you have concerns about the way the CPU "wakes up" after a power failure you might want to consider the RSL5K Power-Up Handler feature.
This capability allows the user to logic program define the way the system returns to functionality after losing control power while in Run/Remote Run Mode.

dbh6 · Feb 28, 2013

@dmargineau, ok but without using the Power-Up handler, i just want to know what happens when power to the plc is lost will it was running then all of the sudden the power is resumed, depending on that answer i may or may not need to have a power-up handler.

dmargineau · Feb 28, 2013

Depending of the hardware used, most of the available output modules' "actions" are configurable within a Safe State mode; this could also be used in case of control power or "master" communications loss.

JHarbin · Feb 28, 2013

dbh6 said:
Hey guys,

So im currently programming a sequences for my pump logic for a project. I have tested the program and so far its "full proof".

I think you mean "fool proof" but there really isn't such a thing...

dbh6 · Feb 28, 2013

@ demargineau ok thanks, @ JHarbin lol, of course their is no such thing as full proof i totally agree with that, you would be surprised by how many "gotcha's" i found in the program

OkiePC · Feb 28, 2013

There's no such thing as idiot proof either, I have been idiot proofing for 20 years and they just keep making better and better idiots.

dbh6 · Feb 28, 2013

@ OkiePC i just had this talk with my colleague today, he was describing pretty what you said an operator will find a way to lock up your system no matter how well you program lol, i was on a service call yesterday and to start a system all you need to do is meet you permissives and hit the start PB "once", however this operator almost always hot it more than 3 times, i asked him why and his reply was "i just want to make sure it comes on" meanwhile in the logic all hell is breaking loose operator's i tell ya

Control Logix "Go to Run" Conditions

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