4. Intrinsic Safety Explosion Protection Instrumentation
4-8
TI 33Q01J30-01E
4.2
Intrinsic Safety Explosion Protection
Instrumentation Using Barriers
Category of Barriers
Classified roughly, barriers includes Zener barriers and insulating barriers (intrinsic safety
barriers). Select the best one as your system, with the knowledge of their future.
(1) Feature of Zener barriers
Zener barrier has a simple construction which consists of just Zener Diode and resistance.
As the circuit of hazardous area and non-hazardous area are not insulated, they request
the single point ground by the bus bar of Zener barriers, so as not to be created the
functionally unfavorable ground loop by double point ground. Moreover, in most countries, it
is impossible to ground circuits in hazardous area.
A power supply for barrier is not required, because Zener barriers carry out the function for
security just with Zener Diode and resistance.
(2) Feature of insulating barriers
On the other hand, insulating barriers does not request intrinsic safety ground because
the place between input and output of them is insulated. It is possible to ground circuits in
hazardous area and use them (single point ground). However, a power supply for barrier is
additionally required.
Considerations for Selection of Barrier
Here is a general explanation about the selection of barrier. On the occasion of implementing
intrinsic safety Explosion Protection instrumentation, select a barrier according to the
manufacture’s specifications and estimates with the equipment.
(1) Approved standard
Make sure the barrier has the approved standard which is required for the installation site.
(2) Cost
Compared Zener barriers to insulating barriers about the general cost of the main unit only
per a channel, the approximate proportion are 1 to 2. Also, insulating barriers request a
power supply.
(3) Volume (dimensions)
Dimensions may influence the number of cabinet in which the barrier is set. Compared
Zener barriers to insulating barriers about the size per a general channel, the approximate
proportion are 1 to 2.
(4) Difficulty of wiring, necessity of insulating hazardous area circuit
Zener barriers always need intrinsic safety ground, and most model of them have the
construction grounded through the bus bar. All the circuit on the same bus bar in hazardous
area and non-hazardous area are grounded to the same electric potential. Moreover, in
most countries, circuits in hazardous area need withstand voltage of 500 Vrms. Therefore, it
is impossible to ground circuits in hazardous area and use them. Insulating barriers impose
no restrictions like this, so it is possible to ground circuits in hazardous area and use them
(single point ground). However, a power supply for barrier is additionally required.
Apr. 25, 2022-00
