VEGA Z728 Zener barriers - Manual (Page 21)

21
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
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te of issu
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Pulse transmission and flow measurement
The simplest method of flow measurement, with or without a
pre-amplifier, is illustrated in the circuit above. The flow meter
sensor generates voltage or current pulses, which are
transmitted to the safe area via the Z728. If the sensor generates sinusoidal signals, e. g. an inductive sensor, a Zener
barrier for alternating polarities can be used, for example the
Z928. The Zener barrier is approved for [EEx ia] IIC.
If the power supply to the flow meter is provided via a 28 V,
300 Ohm barrier and ground, the signal can be transferred via
the diode return of the Z787. When selecting the receiver (counter), consideration must be given to the fact that the high
signal is damped by the diode. The system is approved for
[EEx ia] IIC.
LED display
The simplest and most economical solution is the single-
channel Zener barrier shown above. The nominal supply
voltage is sufficiently low that the end-to-end resistance of the barrier limits the flow of current through the LED to an
acceptable value. Otherwise a current-limiting resistor is
required. The system is approved for [EEx ia] IIC.
Hazardous area Safe area
Output
Flow meter with
pulse output
Z728
x3
CL
1
2
8
7
Hazardous area Safe area
Output
Flow meter with
pulse output
1
4
3
2
8
5
6
7
Z787
x3
x3
Hazardous area Safe area
Z728
x3
CL
1
2
8
7