System Description; Working Principle - Burkert 8626 Instructions De Service

2

SYSTEM DESCRIPTION

2.1

Working principle

The Mass Flow Controller (MFC) Type 8626 is a compact unit for controlling the
mass flow of gases. It maintains a preset value independent of disturbing
parameters such as pressure variations or time-variable flow resistances (e.g. as a
result of filter contamination).
The MFC Type 8626 combines in one unit the components sensor, electronics (with
the functions signal processing, control and valve driver), as well as a proportional
valve that functions as an actuator (Fig.1).
w
p
1
Q-Sensor
Fig.1 Components of MFC Type 8626
Set value setting (w) is done electrically via a standard signal (see 2.3). The
instantaneous value (x) measured by the sensor is compared with the set value in
the control electronics. For the actuating signal, the control transmits a pulse-width
modulated voltage signal to the actuator. The pulse-duty factor of the voltage signal
is varied according to the deviation detected by the control.
The instantaneous value, furthermore, is transmitted via an analog electrical
interface to the outside and is available to the user for checking purposes or for
other modes of exploitation (e.g. measurement of consumption by integration).
Owing to the measurement principle used (see 2.5.1), the MFC Type 8626 works
to a large extent independently from the actual pressure and temperature
conditions in the respective application and features a high dynamic ratio and low
sensitivity to contamination.
The MFC Type 8626 is of modular construction, so that by using different proportio-
nal valves and connection plates, a variant may be built up for each application that
is tailored to its specific fluidic requirements.
Operating Instructions-No. 801 147
x = w-x
d
Regler
x
Control
electronics
Q sensor
y
Stellglied
Actuator
x
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