General Function - Burkert 8626 Instructions De Service

General function

The MFCs of Types 8626 / 8716 / 8713 / 8712 / 8711 / 8710 are compact devices
with which the mass flow of gases is controlled. They control to a preset setpoint
value, independent of disturbances such as pressure variations or flow
resistances that vary with time, e.g. as a result of filter contamination.
The MFCs contain the components flow rate sensor (Q sensor), electronics (with
the functions signal processing, control and valve drive), and a proportional
solenoid valve as the servo component.
w x =w-x
d
x
p
Q sensor
Fig.: Components of a Mass Flow Controller
The setpoint value (w) is set electrically via a standard signal or a field bus. The
process value (x) measured by the sensor is compared in the controller with the
setpoint value. The correcting variable is sent as a plus-width modulated voltage
signal to the servo component. The pulse-duty factor of the voltage signal is varied
according to the control deviation determined.
The process value, in addition, is sent out via an analog electrical interface or a
field bus and is available to the user for monitoring purposes or further evaluation
(e.g. calculation of consumption by integration).
The thermal measurement principle guarantees that the MFCs control to the
required mass flow to a large extent independently of pressure and temperature
variations in the respective application.
The MFMs, in contrast to the corresponding MFCs, do not have a proportional
valve, so that these devices can only be used to measure the mass flow and not
to control it. The characteristics of the other components, described in the
following, in particular the sensors, are identical with those of the MFCs.
8 - MFC/MFM
y
controller
servo
component
x
out