Accidental start of motors when downloading rslogix 5000 project

[davidvu]

Is there something that I can programmatically do to prevent motors from starting when downloading?

 

[James Mcquade]

We try to ensure that the machinery is stopped when uploading programs to the pc.When that doesn't work, we have maintenance walk the line to make sure its clear and safe to download.

I'm not sure about logix 5000, but in the slc 500 software, there is a first scan bit that we use to set the machinery to a just powered up state which turns off all the outputs and sets the machine to a neutral state. we then must select manual or automatic controls on our mmi screens or hmi control screens.

Maybe logix has a first scan bit.

regards,
james

 

[JeremyM]

XIC S:FS

lol

 

[davidvu]

Is there a scenario/setting that would cause the download process itself to energize the digital outputs and start a motor?

 

[Firejo]

Without knowing how the motors are being controlled (VFD, motor starters, etc…) it’s hard to say exactly how to deal with that however I think regardless of the reason to do so I would always ensure that when the PAC is in program mode that nothing can happen (including starting the motor). For example, if you’re controlling a VFD by messaging to it I would also connect the E-stop on the VFD to an output on the PAC and ensure that when in programming mode the output is off. This should disable the drive so anytime you download and the PAC goes into programming mode the drive can’t start and/or will stop if it’s running already

 

[JeremyM]

Is there a scenario/setting that would cause the download process itself to energize the digital outputs and start a motor?

The download alone energizes nothing.

 

[FactoryTalktotheHand]

When you download a program to a processor, you also download the tag data stored in your offline project. If for instance, your motor is started by a boolean tag called MOTOR_START, and your offline project has a 1 in MOTOR_START's value, and there is nothing in your logic to write a zero to it on startup, then scenarios like this will happen.

When you're programming it's best practice to use the first scan bit to initialize your program, shut off any outputs, reset counters and timers, etc. I'm guess what happened is that you uploaded the program while it was running, so when you download, all the tag values will be at the same state the machine was when you last uploaded.

 

[ASF]

You can set the state of each output in the case of a PLC fault or download from the configuration screen for that card - see below. So if your motor is driven directly by an output (e.g. contactor, relay...) you can ensure the output will turn off during a download. If your motor is driven by a VSD over comms then it's slightly less clear. To use the example of a powerflex 525, if I send it a start command, it'll run until it gets a stop command (or faults). If the PLC goes into program mode, it won't send it a stop command, so in theory it could keep running. That's why, by default, there's a setting to stop the drive if it loses comms to it's control source (whether that be ethernet, or the control panel on the drive). So generally, yes, the PF525 would stop as well, but that's contingent on the drive parameters being set the correct way - so you can't truly say that you can do something "programatically" to prevent that.

It goes without saying that before you do a download, you should shut down the whole machine anyway - if nothing is running when you start your download, as long as you haven't set one of your outputs to be on during program mode then I can't see any way that anything could start.

 

[microdesigns2000]

I have seen a couple of [incorrect] installations that use motors controlled by KB controllers which have an "inhibit" input instead of a "run" input. If the designer didn't control the drive with the normally closed contact of a relay, then the drive would run whenever the PLC output is off (including during a PLC download and after a power cycle until the PLC gets into run mode).

Maybe you have a situation like this?

Also, if there is remote I/O involved, or the drive is being controlled like ASF described, some of them can be configured to maintain or change their output states during a communications loss. And if the motor is a servo and under load at the time, there are other things to look at.

davidvu, you didn't mention what kind of motors or the hardware configuration.

 

[PLC GURU]

estop?

 

[rdrast]

estop?

Agree 100%.

First, your program has serious problems, if you are not initializing it to a known (safe) state on transition to run.

Even so, I program all of my PLC's with a dedicated output that sits in the master safety loop (ESTOP). Whenever it is not healthy and in run, the ESTOP loop is opened.

My ESTOP response code in the PLC makes sure to de-energize any sealed in outputs that can cause motion, so that nothing restarts when ESTOP is reset.

You MUST keep safety in mind with every line/rung of code you write.

 

[harryting]

Wow, as others said, you need to fix your program and maybe alter the control panel as well.

RESET to SAFE / DE-ENERGIZED STATE is the first thing you do in a program. Also, electrical design! The master relay should always be opened during a download by DESIGN.

 

[Bit_Bucket_07]

The only time I've witnessed something like that happening, it involved AB soft start and variable frequency drives that were networked on RIO on a PLC5. It was another programmer who downloaded the program, and we never discovered exactly how or why it happened. It wasn't an error in the program logic that caused it. According to the logic, no motors were allowed to start unless the E-Stop circuit had been energized for at least 5 seconds after the first scan bit had transitioned off.