13
P6A
Measuring cables should not be laid parallel to high-tension and control
circuits (e.g. in common cable shafts). If this cannot be arranged, protect the
measuring cable with steel conduit and keep it at least 50cm away from other
cables. Stray fields from transformers, motors and protective contacts are to
be avoided.
6
Differential pressure measurement circuit
Two transducers with the same final scale value can be connected together
without any problem in order to determine the corresponding differential
pressure signals. For this purpose the excitation voltage contacts are
connected in parallel and the measurement voltage contacts are connected in
crossover. The resulting resistance is then 175
W
.
1
2
3
4
2 (bk)
4 (rd)
3 (bu)
1 (wh)
Transducer 1
Transducer 2
1
2
3
4
2 (bk)
4 (rd)
3 (bu)
1 (wh)
2 (bk)
4 (rd)
3 (bu)
1 (wh)
Terminal box VKK
to amplifier
U
B
U
A
U
A
= Differential
pressure signal
U
B
= Bridge excitation
voltage
Fig. 6.1:
Circuit diagram for differential pressure measurement
Excitation voltage
Measurement voltage
Transducer 1
Transducer 2
2 / wh
with
2 / wh
3 / bu
with
3 / bu
1 / wh
with
4 / rd
4 / rd
with
1 / wh
The differential pressure signal is close to: U
A
= 1/2
.
(U
A1
-- U
A2
)
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