Cycle and Response Times of the S7-400
9.7 Examples of Calculating the Cycle Time and Reaction Time
S7-400 Automation System, CPU Specifications
Manual, 10/2006, 6ES7498-8AA04-8BA0
9-21
Calculation of the Longest Response Time
● Longest response time
18.23 ms * 2 = 36.5 ms.
● Delays in the inputs and outputs
– The digital input module SM 421; DI 32xDC 24 V has an input delay of not more than
4.8 ms per channel
– The digital output module SM 422; DO 16xDC 24 V/2A has a negligible output delay.
– The analog input module SM 431; AI 8x13Bit was assigned parameters for 50 Hz
interference frequency suppression. This results in a conversion time of 25 ms per
channel. Since 8 channels are active, a cycle time of 200 ms results for the analog
input module.
– The analog output module SM 432; AO 8x13-bit was programmed for the measuring
range of 0 to 10V. This results in a conversion time of 0.3 ms per channel. Since 8
channels are active, a cycle time of 2.4 ms results. The settling time for the resistive
load of 0.1 ms must still be added. The result is a response time of 2.5 ms for an
analog output.
● All the components are plugged into the central rack; DP cycle times do not therefore
have to be taken into account.
● Case 1: When a digital signal is read in, an output channel of the digital output module is
set. This produces a response time of:
Response time = 36.5 ms + 4.8 ms = 41.3 ms.
● Case 2: An analog value is read in and an analog value output. This produces a response
time of:
Response time = 36.5 ms + 200 ms + 2.5 ms = 239.0 ms.
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