Siemens SIMATIC ET 200AL, System Manual

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What you should know about analog technology
2.17 Cycle time of an analog module
Analog value processing
Function Manual, 06/2014, A5E03461439-AC
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2.17 Cycle time of an analog module
Definition
The cycle time of an analog module represents the time that the module needs to process all
channels used. The cycle time depends on the form of measured value acquisition used, e.g.
multiplex or parallel measured value acquisition.
Sequential measured value processing
This procedure processes the analog channels in the module one after another
(sequentially). For analog inputs, the values are connected to a converter, for example using
a multiplexer, and sequentially converted.
The cycle time of the analog module is derived from the total conversion time of all activated
analog channels of the module. STEP 7 provides the option of deactivating unused analog
channels. to reduce the cycle time.
The figure below gives an overview of the factors that determine the cycle time of an n-
channel analog module.
Figure 2-21 Cycle time of an analog module with multiplex conversion
Parallel measured value acquisition
This procedure processes the analog channels of a module at the same time (in parallel)
rather than one after another. In parallel measured value processing, the cycle time of the
module is usually constant and does not depend on the number of channels used. The goal
of parallel measured value acquisition as it is applied by high-speed analog modules, for
example, is a shorter cycle time. You can find more information on HS modules in the
section High-Speed analog modules (Page 113).