Page 382 - Programmable Logic Controllers, Fifth Edition

L1 Inputs Ladder logic program Outputs L2
Oven_On_Button Oven_O _Button Oven_On_PL
<Local:1:I.Data.1> <Local:1:I.Data.2> <Local:2:O.Data.2>
Oven_On_Button
Oven_On_PL
Oven_On_PL
Oven_O _Button <Local:2:O.Data.2>
Warning_Horn
ON
Oven_On_PL
OFF <Local:2:O.Data.2> TON Heater_Contactor
TIMER ON DELAY EN
Timer Timer_Heat
Preset 10000
Accum 0 DN
Fan_Motor
TOF
TIMER OFF DELAY EN
Timer Timer_Cooling
Preset 300000 DN
Accum 0

Warning_Horn
Timer_Heat.TT <Local:2:O.data.3>

Heater_Contactor
Timer_Heat.DN <Local:2:O.data.4>

Fan_Motor
Timer_Cooling.DN <Local:2:O.data.5>

Figure 15-59 Timer control of a heating oven process.

Tag Name Alias For Base Tag Data Type Style • The Timer_Cooling.DN bit of the TOF timer
Warning_Horn Local:2:O.Data.3 Local:2:O.Data.3 BOOL Decimal becomes true which energizes the Fan_Motor.
Heater_Contactor Local:2:O.Data.4 Local:2:O.Data.4 BOOL Decimal • After 10 s (10000 ms) have elapsed the Timer_Heat.
Fan_Motor Local:2:O.Data.5 Local:2:O.Data.5 BOOL Decimal
Oven_On_PL Local:2:O.Data.2 Local:2:O.Data.2 BOOL Decimal TT bit becomes false to turn off the Warning_Horn
Oven_On_Button Local:1:I.Data.1 Local:1:I.Data.1 BOOL Decimal and the Timer_Heat.DN bit becomes true to
Oven_O _Button Local:1:I.Data.2 Local:1:I.Data.2 BOOL Decimal energize the Heater_Contactor and turn on the
-Timer_Heat TIMER heating coils.
-Timer_Cooling TIMER
• When the Oven_Off_Button is momentarily actu-
Figure 15-60 Tags created for heating oven process. ated the Oven_On_PL output goes false which turns

the pilot light off and opens the continuity of its
seal-in logic path.
in Figure 15-60. Operation of the program can be sum- • The Timer_Heat timer instruction and its DN
marized as follows: bit instruction become false which de-energizes

• Pressing the Oven_On_Button energizes the Oven_ the Heater_Contactor and turns off the heating
On_PL output which seals itself in and enables the coils.
TON and TOF timer instructions. • The Timer_Cooling timer begins accumulating time
• The Timer_Heat.TT bit of the TON timer becomes and the fan continues to operate for the 5 minute
true which sounds the Warning_Horn to warn that (300000 ms) delay period after which the Timer_
the oven is about to come on. Cooling.DN bit becomes false to turn the fan off.

Programming Timers Part 3 363

pet73842_ch15_333-394.indd 363 03/11/15 7:33 PM