Retentive Timer On (RTO) A retentive on-delay timer (RTO) operates the same as a TON timer, except that the retentive timer retains (remembers) its ACC value even if: • The rung goes false. • The processor is placed in the program mode. • The processor faults. • Power to the processor is temporarily interrupted and the processor battery is functioning properly. The ControlLogix RTO retentive on-delay timer instruction is shown in Figure 15-61. The description of the function block fields and tag references are the same as for that of a TON timer; however, a RES reset instruction must be used to reset the accumulated value of a retentive timer. The RES instruction must have the same tag name as the timer you want to reset. Input side of rung RTO RETENTIVE TIMER ON Timer Preset Accum SOL_On_Timer 10000 Input Outputs Limit_Switch <Local:1:I.Data.7> L1 L2 Limit_Switch LS_EN_PL 364 Part 3 Programming Timers An example application of a limit switch 2 minute (120000 ms) RTO timer program is shown in Figure 15‑62. The different tags created to fit the program are shown in Figure 15-63. The operation of the program can be summarized as follows: • The status and value of all instructions, with the timer initially reset, are as shown in the monitor tags window. • When the Limit_Switch has been closed for 1 minute, the status and value of the instructions would be: -- PRE – 120000 -- ACC – 60000 -- LS_Timer.EN – 1 -- LS_Timer.TT – 1 -- LS_Timer.DN – 0 -- LS_EN_PL – 1 -- LS_TT_PL – 1 -- LS_Alarm – 0 • When the Limit_Switch is opened after 1.5 minutes, the status and value of the instructions would be: -- PRE – 120000 -- ACC – 90000 -- LS_Timer.EN – 0 -- LS_Timer.TT – 0 -- LS_Timer.DN – 0 -- LS_EN_PL – 0 -- LS_TT_PL – 0 EN DN 0 SOL_On_Timer RES Figure 15-61 RTO retentive on-delay timer instruction. -- LS_Alarm – 0 Ladder logic program RTO RETENTIVE TIMER ON Timer Preset Accum Figure 15-62 Limit switch RTO timer program. LS_Timer 120000 0 LS_EN_PL LS_Timer.EN <Local:2:O.Data.0> LS_Timer.TT LS_Timer.DN EN DN LS_TT_PL <Local:2:O.Data.1> LS_Alarm <Local:2:O.Data.2> Reset_LS_Timer <Local:1:I.Data.2> LS_Timer RES Reset_LS_Timer LS_TT_PL LS_Alarm Alarm
Petruzella_ProgrammableLogicControllers__5e
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