Siemens SIMATIC ET 200AL, System Manual

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What you should know about analog technology
2.16 Conversion time of an analog module
Analog value processing
Function Manual, 06/2014, A5E03461439-AC
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2.16 Conversion time of an analog module
Basic conversion time and conversion time of an analog input channel
The basic conversion time is the minimum time required by one single channel to convert
analog values. The actual conversion time comprises both the basic conversion time and,
depending on the analog input module used:
●
Processing time for measuring resistance
● Processing time for wire break monitoring
● Processing time for overflow/underflow monitoring
● Processing time for checking common mode errors
Example
This example shows channel 6 of an analog input module for resistance measurement in the
range of 6000 Ω, a configured integration time of 20 ms, and activated wire break
monitoring.
The conversion time of the channel is derived from the total of the following measurement
variables:
Measurement variable Time in
ms
Basic conversion time 27
Processing time for RTD/resistance (6000 Ω) 4
Processing time for wire break monitoring in the RTD/resistance and thermocouple areas 9
Conversion time of the channel 40
Conversion time of the analog output channels
The conversion time of an output channel starts with the transfer of the digital value from the
internal memory of the module and ends with the digital-to-analog conversion.
The conversion time does not include the settling time for the analog signal at the module
terminal. Detailed information on the settling time can be found in Settling and response
times of analog output modules (Page 52).
Note
Relationship between diagnostics and conversion time
While some diagnostics run parallel to the conversion and do not extend the conversion
time, other diagnostics types can lead to an extension of the conversion time, as
demonstrated in the example above.