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8.10.2 Current measurement at the PWMi_H3_X outputs
The current measurement at the PWMi_H3_X outputs is implemented via shunt resistor. The
measuring amplifier has a low-pass filter with R*C = 1 ms. This low-pass filter provides an inte-
gral component.
The arithmetic mean is measured. The CPU measures the current only in the middle of the ON
time of the PWM signal. No ratio of ON time to OFF time is calculated, therefore an integral com-
ponent is necessary for the most correct measurement.
Usually valves already have a good average of the load current due to their self-inductance.
Purely resistive loads can be operated on the controller if the PWM frequency is set to 1 KHz.
The low-pass filter mentioned above is provided for this purpose. For lower frequencies (e.g. 100
Hz) the current measurement at purely resistive loads is too inaccurate.