L1 Inputs Oven_On_Button <Local:1:I.Data.1> Oven_On_PL <Local:2:O.Data.2> Oven_On_PL <Local:2:O.Data.2> Oven_On_Button Oven_O_Button Ladder logic program Timer_Heat.TT Timer_Heat.DN Timer_Cooling.DN Oven_O_Button <Local:1:I.Data.2> ON OFF Figure 15-59 Timer control of a heating oven process. Tag Name Warning_Horn Heater_Contactor Fan_Motor Oven_On_PL Oven_On_Button Oven_O_Button Alias For Base Tag Data Type Style Local:2:O.Data.3 Local:2:O.Data.4 Local:2:O.Data.5 Local:2:O.Data.2 Local:1:I.Data.1 Local:1:I.Data.2 Local:2:O.Data.3 Local:2:O.Data.4 Local:2:O.Data.5 Local:2:O.Data.2 Local:1:I.Data.1 Local:1:I.Data.2 BOOL BOOL BOOL BOOL BOOL BOOL Decimal Decimal Decimal Decimal Decimal Decimal TIMER TIMER Timer_ Heat Timer_ Cooling Figure 15-60 Tags created for heating oven process. in Figure 15-60. Operation of the program can be summarized as follows: • Pressing the Oven_On_Button energizes the Oven_ On_PL output which seals itself in and enables the TON and TOF timer instructions. • The Timer_Heat.TT bit of the TON timer becomes true which sounds the Warning_Horn to warn that the oven is about to come on. TON TIMER ON DELAY Timer Preset Accum Oven_On_PL <Local:2:O.Data.2> Timer_Heat 10000 0 TOF TIMER OFF DELAY Timer Preset Accum Timer_Cooling 300000 0 EN DN EN DN Warning_Horn <Local:2:O.data.3> Outputs Oven_On_PL Heater_Contactor <Local:2:O.data.4> Warning_Horn Fan_Motor <Local:2:O.data.5> L2 Heater_Contactor Fan_Motor • The Timer_Cooling.DN bit of the TOF timer becomes true which energizes the Fan_Motor. • After 10 s (10000 ms) have elapsed the Timer_Heat. TT bit becomes false to turn off the Warning_Horn and the Timer_Heat.DN bit becomes true to energize the Heater_Contactor and turn on the heating coils. • When the Oven_Off_Button is momentarily actuated the Oven_On_PL output goes false which turns the pilot light off and opens the continuity of its seal-in logic path. • The Timer_Heat timer instruction and its DN bit instruction become false which de-energizes the Heater_Contactor and turns off the heating coils. • The Timer_Cooling timer begins accumulating time and the fan continues to operate for the 5 minute (300000 ms) delay period after which the Timer_ Cooling.DN bit becomes false to turn the fan off. Programming Timers Part 3 363
Petruzella_ProgrammableLogicControllers__5e
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