HBM SB01A Montageanleitung Seite 9

SB01A
Hazardous area
Load cell
Fig. 3.1: 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 R
limits the current on terminals 1 and 4 to I
The data for voltage, resistance and short‐circuit current is specified on the
Zener barriers.
The Zener barrier can only limit the voltage and current in the intrinsically safe
circuit effectively if the energy stored in the intrinsically safe circuit is also
limited. Therefore the capacitance and inductance in this circuit, also taking
account of the cable properties, must not exceed defined values.
The SB01A Zener barrier set is intended for operating strain gage full‐bridge
transducers on measuring amplifiers that have a DC bridge excitation.
Grounding Zener barriers
The purpose of the dual‐channel structure of the Zener barrier is not only to
limit the voltage and current between the two channels with terminals 5 and 8,
but also to make sure they are limited relative to the ground potential.
NOTE
In order to operate the barrier safely it must always be grounded
through a potential equalization line.
A1020-4.0 en/de/fr
Safe area
R
1 1
2
x3
3
x3
4
R
1
= U R .
K Z/ 1
Amplifier
8
7
6
5
9
1
HBM