Need assistance with RS Logix Traffic Light program

[parky]

QUOTE: I need to use the same flasher for the red lights when there is a power outage. Then when power restores the program needs to begin at Stage 1 again.
I take this as you want to flash the red lights when power has been lost (how?) if there is no power then how can you flash the lights?.
As for the second part of the question there is usually a first scan bit you can use to reset or force logic to start at stage 1. this is simple if you used a sequence word i.e. first_scan_Bit move 0 to sequence_Word.

 

[drbitboy]

I take this as you want to flash the red lights when power has been lost (how?) if there is no power then how can you flash the lights?.

I was wondering the same thing. However, this is a problem from a college evening course, so that kind of inconsistency is not exactly unexpected.

Maybe there is a battery that comes in when power is lost, and flashing is a safe and low-power option to extend on-battery operation as long as possible. That said, hard-wiring some flashing logic that activates when on battery, instead of using the PLC to do the flashing, would keep the PLC from contributing to the battery drain.

 

[mikeexplorer]

Signal systems going all the way back to early railroad signals had a battery backup in the event of a power failure. The battery backup was not capable of running the entire signal system but would display a "safe" condition on the indicator lights. Depending on the railroad owner, the block occupancy signals would all trip to red (occupied) forcing the train to stop and call in for instructions.



Typically today with 4 way traffic light systems if the power goes out you typically see flashing red light on north/south and flashing yellow on east/west or vice-versa depending on which roadway would be considered more "main rode" (like a state route verses a township road)



For your PLC program you would need an input to detect of line power is on. Input would be set on if normal power is present and would open if power is lost. Then the PLC would know its running on battery backup power and react accordingly.



Mike

 

[Aardwizz]

Only HALF of your job is to make the machine work the way that it is intended. The other half is to handle the cases where it doesn't work as intended.

What actions should be taken if the motor fails to start / valve fails to open?

- How does the PLC know? (Add I/O if needed. Go back to step 5)
- How does the Operator know? Don't assume that he's on the right screen.​

Does the Operator need to respond to some sort of prompt?

- How does the Operator know? Don't assume that he's on the right screen. But be careful you don't flood him with too much "important" info. Data overload is as bad as no data.
- Can he still effectively use the HMI without answering the prompt? Will he ever be getting two prompts at once, and how does that affect your HMI design?
- Are there consequences if he doesn't answer in a timely manner? What should the control system do in that event?​

Presentation is as important as control. If the machine works great, but the operator can't understand what's happening, he'll never fully trust it.

 

[Yin]

James personally we never have time to do debug it just take to long!