Analog Input Scaling¶
The analog input value is converted into digital tics from 0 (representing U_min of the selected input, e.g. -5V) to 4095 (representing U_min of the selected input, e.g. +5V). It is often not practical to have a digital value for an analog sensor since these values must be computed by a separate unit.
This feature allows to do a nonlinear conversion of an analog voltage using a 5th order polynomial function and read the value directly without any other processing unit.
It’s also possible to describe a voltage divider connected to the analog input for sensors that output a resistance as measurement value.
Please follow this wiring scheme when attaching a voltage divider on SOMANET Node.
Some servo drives like the SOMANET Circulo family feature such a voltage divider internally.
Applications include converting the output of a temperature sensor directly into degrees celsius, fahrenheit or any other unit desired by the user.
The converted value will be reflected in Subitem 0x2038:1
The hardware must support at least one analog input
A 5th order polynomial function with or without voltage-divider is supported.
If R:=0 (no internal voltage divider)
If R>0 (user specified pull-up resistor for voltage divider)
The values are specified in object 0x2038, subitems 2-9
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)
Resistance R (0x2038:3): Select the pull-up resistor connected to the selected analog input. Value is given in Ohm.
Constant a0 (0x2038:4): Constant a0 of the polynomial (Offset).
Constant a1 (0x2038:5): Constant a1 of the polynomial (1st order coefficient)
Constant a2 (0x2038:6): Constant a2 of the polynomial (2nd order coefficient)
Constant a3 (0x2038:7): Constant a3 of the polynomial (3rd order coefficient)
Constant a4 (0x2038:8): Constant a4 of the polynomial (4th order coefficient)
Constant a5 (0x2038:9): Constant a5 of the polynomial (5th order coefficient)