3.1.4.1.4.2.2 Software configuration
The object used for this feature is 0x2038 External scaled measurement. The converted value will be reflected in
Subitem 0x2038:1.
The polynomial used for the conversion can be described with the parameters “Constant a0” (0x2038:4) to
“Constant a5” (0x2038:9), which are the coefficients for the polynomial function.
The analog input to be used can be defined using the parameter “Analog input” in subitem 0x2038:2. This
parameter has 5 possible options, which are the 4 standard analog inputs (values: 1-4) and another analog
input called internal (value: 0). The internal analog input is only available in SOMANET Circulo.
Analog input selection k (0x2038:2): Select the scaled measurement source. Values:
1 = Analog Input 1
2 = Analog Input 2
3 = Analog Input 3
4 = Analog Input 4
0 = Internal ADC (if supported, for example SOMANET Circulo 7/9)
The unscaled raw analog input values are filtered through a first order low pass filter before they are scaled.
The cut-off frequency of this low-pass filter can be configured in subitem 0x2038:10.
Note
The external scaled measurement feature is using the filtered analog input value. Therefore all the
analog inputs mentioned in this section are referring to the filtered analog input.
A 5th order polynomial function with or without voltage-divider is supported.
This feature is also designed to have a different behavior depending on the value of the parameter
“Resistance” (0x2038:3). If this value is set to 0, the polynomial will be directly applied to the value of the ADC
count, which has a range of 0-4095 (0 to V ).
If a voltage divider is connected to the analog input, as shown in the figure below, the value of the “Resistance”
parameter (0x2038:3) defines the value of the pull-up resistor R of this voltage divider.
cc
p
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