VEGA Z728 Zener barriers - Manual (Page 15)

15
Zener barriers - operating instructions
Application examples
Subject to reasonable modifications due to technical advances. Copyright Pepperl+Fuchs, Printed in Germany
Pepperl+Fuchs Group • Tel.: Germany +49 621 776-0 • USA +1 330 4253555 • Singapore +65 67799091 • Internet http://www.pepperl-fuchs.com
Da
te of issu
e
05/2
3
/03
0 mA … 20 mA/4 mA … 20 mA transmitter
If a ground-free power supply is available, the use of a single-
channel Zener barrier, grounded in the safe area, represents
the simplest and most economical solution. The ammeter can
be used in combination with a recording instrument, a trip
amplifier, or a 250 Ohm resistance, or replaced by these
devices. In so doing, the overall resistance of the arrangement
must be taken into account. The working range of the barrier caters for an input voltage of up to 27 V. For each built-in
250 Ohm resistance the output voltage of the power supply
can be increased by 1 V. By using a 250 Ohm resistance and a
supply voltage of 28 V, a source of 16.5 V at 20 mA is available
to the transmitter in the hazardous area. The internal voltage
drop across the barrier is then 6.5 V. The system is approved
for [EEx ia] IIC.
With this 2-channel Zener barrier, it is possible to supply a
number of circuits with one source. All the wiring is quasi
ground-free. The maximum voltage supply is 27 V. The internal
voltage drop across the barrier is 7.8 V at 20 mA, so that
19.2 V are available for the field device and ammeter. If the ammeter for converting the current signal into a 1 V … 5 V
voltage signal is replaced by a 250 Ohm resistance, then
14.2 V are available at the field device. The system is
approved for [EEx ia] IIC.
Hazardous area Safe area
A
Z728
x3
CL
1
2
8
7
Hazardous area Safe area
Z788
x3
x3
1
2
3
4
8
7
6
5
A