External scaled measurement

The analog input value is converted into digital ticks from 0 (representing U min of the selected input, e.g. -5V) to 4095 (representing U max of the selected input, e.g. +5V) which must be computed externally for further use.

This feature allows a nonlinear conversion of one of the available analog inputs using a polynomial function up to 5th order and to read the value directly.

It’s also possible to describe a voltage divider connected to the analog input for sensors that output a resistance as measurement value.

Use case: Temperature sensor

Applications include converting the output of a temperature sensor directly into degrees Celsius, Fahrenheit or any other unit desired by the user.

For details about using temperature sensors please check our System integration guide.

Use case: Torque sensor

Applications include converting the output of a torque sensor directly into mNm, Nm or any other unit desired by the user.


  • The hardware must support at least one analog input



For SOMANET Node, please follow this wiring scheme when attaching an external voltage divider.

Drives of the SOMANET Circulo family has a voltage divider internally.

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.


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 cc).

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 p of this voltage divider.

  • V cc represents the value of voltage at which the ADC is connected to, causing the ADC to count an output of 4095.

  • R p represents the pull-up resistor.

  • R th is a resistive sensor, e.g. a thermistor or strain gauge.

  • V in is the voltage that is connected to the selected analog input.

The cut-off frequency of the low-pass filter (0x2038:10) for the analog input can also be tweaked to further fine-tune the unscaled analog input before feeding it to the scaling algorithm.


Upper and lower level thresholds can be configured in subitems 0x2038:11 and 0x2038:12. When these thresholds are breached an error is triggered in the Error report object.


When the value approaches 95% of the defined thresholds, a warning is triggered.


If R p := 0 (no voltage divider)

y(u_k) = a_5 \cdot u_k^5 + a_4 \cdot u_k^4 + a_3 \cdot u_k^3 + a_2 \cdot u_k^2 + a_1 \cdot u_k + a_0

If R p > 0 (user specified pull-up resistor for voltage divider)

y(u_k) = a_5 \cdot R_{th}^5 + a_4 \cdot R_{th}^4 + a_3 \cdot R_{th}^3 + a_2 \cdot R_{th}^2 + a_1 \cdot R_{th} + a_0


R_{th} = \frac {u_k} {4096} \cdot \frac {R_p} {1- \frac {u_k} {4096}}

The coefficients and the pull-up resistor values are specified in object 0x2038, subitems 2-9

  • 0x2038:3 (Resistance R): Select the pull-up resistor connected to the selected analog input. Value is given in Ohm.

  • 0x2038:4 (Constant a0): Constant a0 of the polynomial (Offset).

  • 0x2038:5 (Constant a1): Constant a1 of the polynomial (1st order coefficient)

  • 0x2038:6 (Constant a2): Constant a2 of the polynomial (2nd order coefficient)

  • 0x2038:7 (Constant a3): Constant a3 of the polynomial (3rd order coefficient)

  • 0x2038:8 (Constant a4): Constant a4 of the polynomial (4th order coefficient)

  • 0x2038:9 (Constant a5): Constant a5 of the polynomial (5th order coefficient)