Page 383 - Programmable Logic Controllers, Fifth Edition - Mobile version

Retentive Timer On (RTO) An example application of a limit switch 2 minute
(120000 ms) RTO timer program is shown in Figure 15-62.
A retentive on-delay timer (RTO) operates the same The different tags created to fit the program are shown in
as a TON timer, except that the retentive timer retains Figure 15-63. The operation of the program can be sum-
( remembers) its ACC value even if: marized as follows:

• The rung goes false. • The status and value of all instructions, with the
• The processor is placed in the program mode. timer initially reset, are as shown in the monitor
• The processor faults. tags window.
• Power to the processor is temporarily interrupted • When the Limit_Switch has been closed for 1 min-
and the processor battery is functioning properly. ute, the status and value of the instructions would be:
The ControlLogix RTO retentive on-delay timer in- - PRE – 120000
struction is shown in Figure 15-61. The description of the - ACC – 60000
function block fields and tag references are the same as - LS_Timer.EN – 1
for that of a TON timer; however, a RES reset instruction - LS_Timer.TT – 1
must be used to reset the accumulated value of a retentive - LS_Timer.DN – 0
timer. The RES instruction must have the same tag name - LS_EN_PL – 1
as the timer you want to reset. - LS_TT_PL – 1
- LS_Alarm – 0
• When the Limit_Switch is opened after 1.5 minutes,
RTO
RETENTIVE TIMER ON EN the status and value of the instructions would be:
Timer SOL_On_Timer - PRE – 120000
Preset 10000 DN - ACC – 90000
Accum 0
Input side of rung - LS_Timer.EN – 0
- LS_Timer.TT – 0
SOL_On_Timer - LS_Timer.DN – 0
RES - LS_EN_PL – 0
- LS_TT_PL – 0
Figure 15-61 RTO retentive on-delay timer instruction. - LS_Alarm – 0

Input Ladder logic program Outputs
L1 Limit_Switch L2
<Local:1:I.Data.7>
RTO
Limit_Switch RETENTIVE TIMER ON EN LS_EN_PL
Timer LS_Timer
Preset 120000 DN
Accum 0
LS_EN_PL LS_TT_PL
LS_Timer.EN <Local:2:O.Data.0>

Reset_LS_Timer
LS_TT_PL LS_Alarm Alarm
LS_Timer.TT <Local:2:O.Data.1>

LS_Alarm
LS_Timer.DN <Local:2:O.Data.2>

Reset_LS_Timer
<Local:1:I.Data.2> LS_Timer
RES

Figure 15-62 Limit switch RTO timer program.

364 Part 3 Programming Timers

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