Control Electronics - Burkert 8626 Instructions De Service

Control electronics

Processing of the setpoint and actual flow signals, and drive of the actuator are
carried out by a microprocessor.
The sensor signal is filtered by the control electronics and with the aid of the
calibration curve stored in the device, converted to a value corresponding to
actual flow rate.
In order that critical process, in which a too great flow change is not permitted, can
also be controlled, a ramp function can be activated via the software
"MassFlowCommunicator" (see Appendix C). Here the parameters for rising and
sinking setpoinds can be set separately. Further details on the ramp function can
be taken from the software documentation.
Actuating signal:
actuating signal
xd
The actuating signal is processed according to a PI algorithm.
The control parameters are set in the factory according to type. In order to take
into account the characteristics of the controlled member, the controller works with
member-dependent amplification factors. During the running of the Autotune
routine, these are determined automatically.
In the device a parameter is stored with which the control dynamics can be altered
with the software "MassFlowCommunicator". Its extreme values correspond on
the one hand to very rapid correction, whereby overswing is possibly accepted,
and on the other hand to a slow asymptotic correction to the desired flow rate. The
first can lead to immediate reaction of the controller to very small actuating signals,
whereby the control can become very unsteady. With less dynamic processes,
the controller behaviour can be damped, so that small variations in the process
value or setpoint are corrected only slowly.
As the correcting variable, a pulse-width modulated (PWM) signal is sent to the
proportional valve. The frequency of this signal is adapted to the respective valve.
To assure the tight-closing function of the valve, zero-point switch-off is built in.
This becomes active if the following conditions simultaneously occur:
setpoint
and process value
With the zero-point switch-off activated, the PWM signal is set to 0 %, so that the
valve closes completely.
1 ) With types 8711 / 8712 / 8713 higher control ranges on request.
= setpoint
= w
< 2 % of nominal flow
< 2 % of nominal flow
- process value
- x
1)
MFC/MFM - 13