3. Intrinsic Safety Explosion Protection Instrumentation
3-9
TI 32S01J30-01E
(5) Failure rate
The construction of Zener barriers is simple, because they carry out the function for security
just with Zener Diode and resistance. On the other hand, insulating barriers consist of
various parts, because they have the function of insulation and energy restriction. Therefore,
the failure rate of insulating barriers is generally higher than that of Zener barriers. In
Zener barriers, problems are usually solved by replacement and, in insulating barriers by
modification.
(6) Accuracy, response
In general, Zener barriers have advantages about accuracy and response, because
insulating barriers usually have more complex signal path than Zener barriers.
(7) Withstand voltage
Withstand voltage is a rating which only insulating barriers have. Most of the models have
250 V or more AC/DC, so there’s almost no problem at the time of instrumentation.
(8) Security rating
Security rating indicates the scale of energy that can be occurred in hazardous area of
barrier in the case of the accident. It is usually described by the signage, such as Uo=n V,
Io=n mA, Po=n W, Co=n µF, Lo=n mH (Um=n Vrms or DC: only insulating barriers).
(In FM standard, it is called entity parameter, including the parameter of (10), and is
described such as Voc=n V, Isc=n mA, Ca=n µF, La=n mH).
(9) Permissible cable parameter
Permissible cable parameter indicates the scale (capacity, inductance) of hazardous area
circuit (including cables) which can be connected to barriers. It is regulated by a barrier
and a kind of gases. It is usually described by group (ex. IIC etc.=a kind of gases), n µF
(capacity), n mH or n µH/Ω (inductance or L/R ratio).
(10) Voltage in non-hazardous area
In regards to Zener barriers, Vwkg (maximum working voltage) and Vmax (maximum
permissible voltage) are regulated. In regards to insulating barriers, regulation of voltage
is for power supply rating only, but the use conditions of circuit in non-hazardous area are
different by models.
(11) Influence by resistance value between input and output
This is a matter of only Zener barriers. As resistance and fuse exist between terminals of
input and output in a barrier, in regards to an application that pass an electric current, it is
necessary to take account of voltage drop inside the barrier. Moreover, in some application,
it is necessary to take account of Diode current leakage (usually several µA).
Apr. 25, 2022-00
