Page 380 - Programmable Logic Controllers, Fifth Edition - Mobile version

Ladder logic program
L1 Input Timer_Button Green_PL Output L2
<Local:1:I.Data.0> <Local:2:O.Data.3> TON
Timer_Button L TIMER ON DELAY EN
Timer Pilot_Light_Timer Green_ PL
Pilot_Light_Timer.EN Preset 20000 DN
Accum 0

Green_PL
Pilot_Light_Timer.DN Pilot_Light_Timer <Local:2:O.Data.3>
RES U

Figure 15-54 Pilot light TON timer.

• Momentary detection of the target by the SOL_ • When the button is then opened the timer rung
Deenergize_Sensor causes the opening of its con- remains true through the logic path created by the
tacts and resets the program to its original state. Pilot_Light_Timer.EN bit.
Figure 15-54 shows a program that uses a TON timer to • After 20000 ms (20 s) have elapsed the timer DN
illuminate a green pilot light for 20 seconds each time a mo- bit is set to reset the timer to its original state and
mentary button is pressed. In addition to the TON timer this unlatch the Green_PL and switch it off.
program uses multiple outputs on one rung, output latch and The ControlLogix program of Figure 15-55 shows
unlatch instructions, as well as a timer reset instruction. The three TON timers cascaded (connected together) for traf-
operation of the program can be summarized as follows: fic light control. The ladder logic used is the same as that
• Initially closing the Timer_Button sets (latches) the used to program the traffic lights using the SLC 500 con-
Green_PL on and enables the Pilot_Light_Timer. troller. The different tags created to fit the program are

Ladder logic program Outputs
Amber_Light_Timer.DN
TON
TIMER ON DELAY EN L2
Timer Red_Light_Timer
Preset 30000 DN Red_ Light
Accum 0

Red_Light_Timer.DN Amber_ Light
TON
TIMER ON DELAY EN
Timer Green_Light_Timer Green_ Light
Preset 25000 DN
Accum 0
Green_Light_Timer.DN
TON
TIMER ON DELAY EN
Timer Amber_Light_Timer
Preset 5000 DN
Accum 0
Red_Light
Red_Light_Timer.EN Red_Light_Timer.DN <Local:2:O.Data.0>

Green_Light
Green_Light_Timer.EN Green_Light_Timer.DN <Local:2:O.Data.1>

Amber_Light
Amber_Light_Timer.EN Amber_Light_Timer.DN <Local:2:O.Data.2>

Figure 15-55 ControlLogix traffic control program.

Programming Timers Part 3 361

pet73842_ch15_333-394.indd 361 03/11/15 7:33 PM