Japagaijin
Member
I am stuck on where to put the 5th timer to put a 3 second delay on the red light in the traffic light program. I have a pic of my plc rungs here
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Red light delay PLC Help
- Thread starter Japagaijin
- Start date
the_msp
Lifetime Supporting Member
Welcome!
Post your pic and we can help.
Post your pic and we can help.
Japagaijin
Member
OP
Photo add
Trying to add pic, having trouble
Trying to add pic, having trouble
Japagaijin
Member
OP
drbitboy
Lifetime Supporting Member
add delay to red N/S or to red E/W? add delay to transition to on or to off?
if to both red N/S and to red E/W, then with your current design, I think you need a fifth and a sixth timer (maybe TOFs)
With a re-design, I think you can get away with one timer total.
if to both red N/S and to red E/W, then with your current design, I think you need a fifth and a sixth timer (maybe TOFs)
With a re-design, I think you can get away with one timer total.
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Japagaijin
Member
OP
Help!!
I need both sides to be on the same delay. Both red lights need to be on for 3 seconds together before the next green cycle starts
I need both sides to be on the same delay. Both red lights need to be on for 3 seconds together before the next green cycle starts
drbitboy
Lifetime Supporting Member
No new timers required. Changes to [Red N/S] and [Green N/S] shown below; similar code for [Red E/W] and [Green E/W] is left for OP as an exercise.
drbitboy
Lifetime Supporting Member
Single-timer approach using .ACC: assumes symmetrical operation across directions; includes 3s delay/overlap with both directions red (shown).
Roughly the same number of instructions as OP (2-3doz), but provides separation of concerns:
.
Caveats
Roughly the same number of instructions as OP (2-3doz), but provides separation of concerns:
- Timing-related logic on rungs 0-2
- Single timer with breakpoints, plus [N/S half-cycle] bit, means all timing requirements need be written once only (rung 2)
- Light logic on rungs 3-6
- Probably busier than it needs to be e.g. take my "Green or Yellow" bit. Please.
- Intrinsically safe logic(?)
- Opposite directions' Greens/Yellows dependent on [N/S half-cycle] bit
- Red lights dependent on same-direction green and yellow only, not timing
.Caveats
- It is unlikely that this is the the first instance of this approach
- I thought this would be cleaner than the cascading timers of OP, and the separation of concerns does help, but in the end it's clarity is less than expected.
- SQO-driven or similar would be much cleaner and is probably the best way.
- This approach will probably not scale to more complex intersections e.g. turn arrows, sensors.
- GRTs should compare against 299 and 2499, not 300 and 2500
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