Demonstrate Function Check of Zener Barrier

A

Thread Starter

Akdas

Hi
can you help how to function check of Zener Barrier??
i belive if its in the system we can inject mA but can we do the same if its out of the sys.?
thanks
Akdas,
 
1. removal and testing
The Crouse-Hinds/MTL app note AN9003 - A Users Guide to Intrinsic Safety discusses removal and testing.
http://tinyurl.com/nkd4fwq

That section is quoted below:

3.4 Testing of apparatus
Sometimes it is suggested that apparatus should be removed for periodic testing. In practice, if an intrinsically safe loop is functional then it is very unlikely to have failed in a dangerous mode. Components critical to safety are derated, so the probability of external circumstances causing them to fail without causing a malfunction is small.

There is a bigger risk that a mistake could be made during the removal and replacement of the apparatus being tested. The argument for not interfering with a system, which has survived the
initial inspection and is still functional, is very powerful.

A particular case sometimes cited is regarding shunt-diode safety barriers. Failure rate statistics can always be questioned, but the undetected failure rate to danger of a barrier (i.e. the shunt diodes not failing to an open circuit condition), can be readily demonstrated to be in better than 10^-10/annum. With this probability of failure they should remain untouched forever. If they are removed for any other reason a simple continuity check has some merit.

2. Inspection test

The ANIS/ISA RP 12.06.01-2003 standard offers the following points for inspection of an I/S system:

6.3.1 The location classification and the suitability of the intrinsically safe system for that classification should be verified. This includes verifying that the class, group, and temperature ratings of both the intrinsically safe apparatus and the associated apparatus agree with the actual classification of the location.

6.3.2 Prior to energizing an intrinsically safe system should be inspected to ensure that the

a) installation is in compliance with the documentation;

b) intrinsically safe circuits are properly separated from nonintrinsically safe circuits;

c) cable shields are grounded in accordance with the installation documentation;

d) modifications have been authorized;

e) cables and wiring are not damaged;

f) bonding and grounding connections are tight;

g) bonding and grounding hardware is not corroded;

h) resistance of any grounding conductor, including termination resistance from shunt-type-associated apparatus to the grounding electrode does not exceed one ohm;

i) protection has not been defeated by bypassing; and

j) check for signs of corrosion on the equipment and connections.

3. performance
Given

- the high probability that an I/S barrier will fail safe and the inverse; the low probability that an I/S barrier will fail unsafe

- a barrier with a blown fuse is dysfunctional
does not performance in an analog loop confirm a barrier's functionality?
 
Top