Automationdirect.com D4-454 PLC User Manual page 393

Using a Timer Inside a Stage
The finished modified program is shown to the right. The
shaded areas indicate the program additions.
In the Push-UP stage S1, we add the Set Stage Bit S6
instruction. When contact X0 closes, we transition from
S1 and go to two new active states: S2 and S6. In the
Push-DOWN state S4, we make the same additions. So,
any time someone presses the door control pushbutton,
the light turns on.
Most new stage programmers would be concerned about
where to place the Light Stage in the ladder, and how to
number it. The good news is that it doesn't matter!
• Just choose an unused Stage number, and use
it for the new stage and as the reference from
other stages.
• Placement in the program is not critical, so we
place it at the end.
You might think that each stage has to be directly under
the stage that transitions to it. While it is good practice,
it is not required (that's good, because our two locations
for the Set S6 instruction make that impossible). Stage
numbers and how they are used determines the transition
paths.
In stage S6, we turn on the safety light by energizing Y3.
Special relay contact SP1 is always on. Timer T0 times at
0.1 second per count. To achieve 3 minutes time period,
we calculate:
K = 3 min. x 60 sec/min
K = 1800 counts
The timer has power flow whenever stage S6 is active.
The corresponding timer bit T0 is set when the timer
expires. So three minutes later, T0=1 and the instruction
Reset S6 causes the stage to be inactive.
While Stage S6 is active and the light is on, stage
transitions in the primary path continue normally and
independently of Stage 6. That is, the door can go up,
down, or whatever, but the light will be on for precisely
3 minutes.
Chapter 7: RLLPLUS Stage Programming
0.1 sec/count
D4-454 PLC User Manual, 1st Edition, Rev. D
ISG
DOWN State
S0
X0
SG
Push–UP State
S1
X0
SG
RAISE State
S2
SP1
X1
SG
UP State
S3
X0
SG
Push–DOWN State
S4
X0
SG
S5 LOWER State
SP1
X2
SG
LIGHT State
S6
SP1
TMR
K1800
T0
7-13
S1
JMP
S2
JMP
S6
SET
Y1
OUT
S3
JMP
S4
JMP
S5
JMP
S6
SET
Y2
OUT
S0
JMP
Y3
OUT
T0
S6
RST