Siemens Simatic SM331 Getting Started page 38

Configuration of the SIMATIC Manager
6.2 Hardware configuration
Explanation of the individual settings
Measuring type:
2DMU and 4DMU stand for 2-wire and 4-wire current transducers
--- means that the channels are deactivated. If you deactivate channels, the remaining
channels are processed faster.
Measuring range modules
The required setting of the measuring range module is displayed.
Interference frequency (Interference frequency suppression)
The frequency of your AC power system can interfere with the measured value, particularly
when measuring in low voltage ranges and using thermocouple elements. With this
parameter you specify the frequency of your power supply on site.
This parameter also influences the granularity, integration time and the basic execution
period of the channel group.
● Resolution (accuracy)
● Integration time
● Basic processing time
Resolution
9 bits
12 bits
12 bits
14 bits
Hardware interrupt:
Only the channels 0 and 2 have hardware interrupt capabilities. You can use hardware
interrupts to trigger an alarm when the analog signal exceeds its high or low limit.
Finish the hardware configuration:
Close the window with the configuration.
Compile and save the project with the command Station > Save and Compile (Ctrl+S)
This completes your hardware configuration for the project.
6-12
The analog value is stored in a 16-bit word.
The module requires a certain amount of time to measure the analog signal. This time is
called integration time. The higher the required accuracy is, the longer the module needs
for measuring the voltage.
Besides the integration time, the module also needs a certain amount of time to provide
the binary value.
Relationship between accuracy, interference frequency and integration period
Interference
frequency
400 Hz
60 Hz
20 Hz
10 Hz
Integration time
2.5 ms
16.6 ms
20 ms
100 ms
SM331; AI 8x12 Bit Getting Started part 1: 4 -20mA
Getting Started, 11/2006, A5E00253410-02
Basic processing time
24 ms
136 ms
176 ms
816 ms