Control Electronics - Burkert 8626 Instructions De Service

2.5.2. Control electronics

Processing of the current set and instantaneous flow signals and the drive of the
actuator are carried out in the microprocessor electronics.
The analog voltage signal from the sensor is filtered by the control electronics,
digitized and converted with the aid of a calibration curve stored in the EEPROM into
a digital value proportional to the instantaneous flow rate. Its deviation from the set
value, which has also been digitized, is processed according to a PI control
algorithm. The final output is the pulse-duty factor of a PWM signal as an analog
correcting variable (Fig.1). If the flow rate is too low, the pulse-duty factor and hence
the valve opening are increased and vice versa.
The current flow rate is transmitted to the outside as a standard signal, referred to
the nominal flow rate in each case, via an analog interface.
The control parameters, the PWM frequency and the cycle time, adjusted to the
actuator valve in each case, are laid down by the manufacturer during calibration.
The control parameters are set such that after a change in set value, the MFC
reaches the new set value in as short a time as possible without overshoot. The 5%
band about the new set value, for example, is reached for a jump from 0 to 90% after
max. 500 ms and not left again thereafter.
Operating Instructions-No. 801 147 35