VEGA Z728 Zener barriers - Manual (Page 14)

14
Zener barriers - operating instructions
Application examples
Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany
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Da
te of issu
e
05/2
3
/03
Temperature measurement
The circuit arrangement shows the connection of a Pt100 in 3-
wire technology, using the 3-channel Zener barrier Z954. The
whole system is quasi ground-free. All 3 barriers have identical end-to-end resistances, so that the resulting error is restricted
to a minimum. The system is approved for [EEx ia] IIC.
The circuit consists of a system of a maximum of seven
Pt100s. The Pt100s are connected in series to a constant
current source. Each voltage signal is transferred to a receiver
via a Z954. The Z954s have been selected due to their high end-to-end
resistance. Due to the high input resistance of the receiver, the
high end-to-end resistance has practically no effect on the
accuracy of measurement.
Hazardous area Safe area
Test circuit
1
3
2
4
Z954
x3
x3
x3
x3
x3
x3
8
6
7
5
Hazardous area Safe area
Receiver with
galvanically
isolated inputs
Z961
x3
x3
x3
x3
1
2
3
4
8
7
6
5
Z954
x3
x3
x3
x3
x3
x3
1
3
2
4
8
6
7
5
1
3
2
4
8
6
7
Z954
x3
x3
x3
x3
x3
x3 5