Siemens SIMATIC S7-300 Series Reference Manual page 137

S 1. Intermediate calculation: Timebase for the calculation of S7 timer
processing time is the sum of all times mentioned above:
2 0.36 ms
+ 2 0.23 ms
+ 2 1 ms
+ 2 2.3 ms
S Processing time of S7 timers
Time required for a single update of 56 S7 timers: 56 8 ms = 448 ms [ 0.45
ms.
Since the S7 timers are called every 10 ms, a maximum of one call can be
made in the cycle time, i.e. the cycle time can be increased through the S7
timers by a maximum of 0.45 ms.
S 2. Intermediate calculation:The response time without I/O delay is formed by
the sum of
8.0 ms
+ 0.45 ms
=8.45 ms.
S Delay times of the inputs and outputs
– The SM 321 The maximum delay time of the DI 32DC 24 V digital input
module is 4.8ms per channel.
– Output delay of the digital output module SM 322; DO 16 DC 24 V/0.5A
can be ignored.
– The SM 331; AI 8 12bit analog input module was configured for an
interference frequency suppression of 50 Hz. This yields a conversion time
of 22 ms per channel. Since 8 channels are active, the cycle time for the
analog input module is 176 ms.
– Analog output module SM 332 AO 4 12–bit was configured for a
measurement range of 0 ...10V. The conversion time is 0.8 ms per channel.
Thus, 4 active channels result in a cycle time of 3.2 ms. To be added is the
settling time of 0.1 ms for ohmic loads. Thus, the response time at the
analog output is 3.3 ms.
S Response times with delay times for inputs and outputs:
S Case 1: A digital output module channel is set after a digital input signal is
received. This results in a response time of:
Response time = 4.8 ms + 8.45 ms = 13.25 ms.
S Case 2: An analog value is fetched and an analog value is output. This results
in a response time of:
Response time = 176 ms + 8.45 ms + 3.3 ms = 187.75 ms.
PLC S7-300, CPU Specifications CPU 312 IFM to CPU 318-2 DP
A5E00111190-01
Cycle and Reaction times
(Input process image transfer time)
(Output process image transfer time)
(Operating system cycle time)
User program cycle time) [7.8 ms.
(result of the first intermediate calculation)
(S7 timer processing time)
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