BD Sensors AX18-DPT200 Betriebsanleitung Seite 45

6.3 Schematic circuit design
The operation of an intrinsically safe device in an explosion hazard area demands that
special care be taken when selecting the necessary Zener barrier or supply isolating de-
vices if the device's properties are to be utilised to their full extent.
The following diagram shows a typical arrangement of power supply, Zener barrier and
pressure transmitter.
Pressure transmitter
+U
U
B
Ex area
Pressure transmitter
Fig. 3 Wiring diagram
Also take note of Point (17) of the type examination certificate, which stipulates
special conditions for intrinsically safe operation.
6.4 Description of example circuit
The supply voltage provided by the power supply of, for example, 24 V
the Zener barrier. In the Zener barrier are series resistors and Zener diodes that act as
protective components. The operating voltage is then passed on to the device, and a
signal current flows that depends on the pressure.
Danger of death from explosion
The use of intrinsically safe devices as
-
Zone 0 equipment is permitted only when
they are powered using a floating galvanic
DANGER
isolator.
6.5 Functional selection criteria for Zener barriers and supply isolators
The supply voltage must not fall below the minimum supply voltage U
otherwise its correct functioning cannot be guaranteed. The minimum supply voltage is
given in the corresponding product specification data sheet under "Output signal / auxiliary
power".
When using a galvanic isolator with a linear limiter, it is important to note that the linear
limiter lowers the clamping voltage of the device, as is also the case for a Zener barrier.
Furthermore, it must be noted that a certain voltage drop also arises across an optionally
used isolating signal amplifier, which then causes an additional drop in the operating volt-
age of the pressure transmitter.
Zener barrier
+U
B B
-U
B
Safe area
Shielded cable
Power feed
Isolating
amplifier
Power
passes across
DC
for the device,
Bmin
45
EN