EB 6111 EN
5
Description
2
Description
2.1
Application
The device is used to convert a direct current
input signal into a pneumatic output signal
for measuring and control tasks.
It is particularly suitable as an intermediate
element between electric measuring devices
and pneumatic controllers or between elec-
tric control devices and pneumatic control
valves.
The input is a load-independent direct cur-
rent of 4 to 20 mA or 0 or 20 mA.
The output is a pneumatic signal of 0.2 to
1 bar or other signal ranges up to max.
8 bar.
2.2
Principle of operation
See Fig. 1 on page 7.
The devices consist of an i/p converter mod-
ule and a downstream volume booster.
When operated, the supplied direct current i
flows through the plunger coil (2) located in
the field of a permanent magnet (3). At the
balance beam (1), the force of the plunger
coil, which is in proportion to the current, is
balanced against the force of the dynamic
backpressure p
K
, which is produced on the
flapper (6) by the air jet leaving the nozzle
(7). The supply air (9) flows to the bottom
chamber of the volume booster (8) and a
certain amount of air determined by the dia-
phragm position flows past the sleeve (8.5)
and leaves through the output (OUTPUT 36).
The output signal p
A
is used also to supply
the nozzle (7). The offset spring (8.2) ensures
that the output signal is at least 100 mbar
even at an input signal of 0 mA. As the input
current and the forces acting on the plunger
coil increase, the flapper (6) moves closer to
the nozzle (7).
This causes the backpressure p
K
upstream of
the restriction (8.4) increase until it corre-
sponds with the input current.
The increasing backpressure pushes the dia-
phragm (8.3) and the plug sleeve (8.5)
downwards. As a result, the supply air caus-
es the output pressure p
A
to increase until a
new state of equilibrium is reached in the di-
aphragm chambers.
When the backpressure p
K
drops, the dia-
phragm moves upwards, releasing the plug
sleeve. The output pressure p
A
can escape
through the sleeve until the forces are equal
again.
Volume booster
See Fig. 1 on page 7.
Booster
I
(top
diagram)
II
(bottom
diagram)
Output signal
0.1 bar or
higher
0.0 bar or
higher
i/p converter
module
Type 6109
or
Type 6112
Type 6112
only
Note:
A relatively stable supply air network
is required for the version with volume
booster II.
