Siemens SIMATIC S7-200 System Manual page 213

Tip
To guarantee that the output of a self-resetting timer is turned on for one scan each time the
timer reaches the preset value, use a normally closed contact instead of the timer bit as the
enabling input to the timer.
Example: SIMATIC Self-Resetting On-Delay Timer
Timing Diagram
current = 100
current = 40
T33 (current)
T33 (bit)
Example: SIMATIC Off-Delay Timer
Timing Diagram
I0.0
current = 100
T33 (current)
T33 (bit) Q0.0
Network 1
LDN M0.0
TON T33, +100
Network 2
LDW>= T33, +40
= Q0.0
Network 3
LD T33
= M0.0
0.4s 0.6s
M0.0
Q0.0
Network 1
LD I0.0
TOF T33, +100
Network 2
LD T33
= Q0.0
1 s
S7-200 Instruction Set
//10 ms timer T33 times out after
//(100 x 10 ms = 1s)
//M0.0 pulse is too fast to monitor
//with Status view
//Comparison becomes true at a
//rate that is visible with Status view.
//Turn on Q0.0 after (40 x 10 ms)
//for a 40% OFF/60% ON waveform
//T33 (bit) pulse too fast to monitor
//with Status view
//Reset the timer through M0.0 after
//the (100 x 10 ms) period
//10-ms timer T33 times out after (100 x 10 ms = 1s)
//I0.0 ON- -to- -OFF=T33 enabled
//I0.0 OFF- -to- -ON=disable and reset T33
//Timer T33 controls Q0.0 through timer contact T33
0.8 s
Chapter 6
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