Principle - HBM SD01A Bedienungsanleitung

SD01A

2.5 Principle

Safety barriers form the interface between intrinsically safe and
non-intrinsically safe circuits. It is their task to limit the energy transmitted from
the non-Ex area to the Ex area, both in normal operation and in the event of a
fault.
The barrier limits the current and voltage in the intrinsically safe circuit if the
voltage on the non-intrinsically safe side reaches excessively high values or if
a short circuit occurs on the intrinsically safe side.
In normal operation the voltage between terminals 7 and 8 or 5 and 6 is less
than the breakdown voltage Uz of the Zener diodes, and therefore there is
only a small leakage current through the diodes.
Ex area
Sensor
Fig. 2.1: Schematic diagram of the internal structure of a Zener barrier
If the voltage between terminals 7 and 8 or 5 and 6 increases beyond the
breakdown voltage of the diodes, the Zener diodes become conducting. If the
current is too high, the fuse trips and protects the Zener diodes from
overloading.
If the fuse is destroyed the damage is irreparable, and the whole barrier has
to be swapped out.
In the event of a short circuit on the intrinsically safe side, the resistance R1
limits the current on terminals 1 and 4 to Ik = Uz / R1.
The data for voltage, resistance and short-circuit current is specified on the
Zener barriers.
A1045−2.4 en/de/fr
Non-Ex area
1
R1
3x
2
3
4
3x
R1
8
7
Amplifier
6
5
HBM
9