We have a position feedback transducer for a control valve requiring 24VDC for its functioning. This transducer is not categorized for hazardous area application. Can we not connect a barrier in control room to make this transducer functional in hazardous

What is the significance and consequence?

 

No - just connecting a device downstream of an IS barrier or isolator does not make the system intrinsically safe. You can still store enough energy in internal capacitance or inductance in the device to make a bang.

In an IS system, everything connected on the protected or field side of the barrier must either be certified as IS or meet the requirements of "simple apparatus" (no energy storage and power/voltage/current levels below specified values.)

Cheers,
Bruce.

 

Hello Bruce:

From what I've read so far and what you've said seems to confirms this, instruments connected to barriers must be rated for IS service. Instruments rated for IS service ensures they do not store enough energy to be an ignition source. Simply have an IS Barrier does not make the loop IS, so if you have a general purpose instrument and put an IS barrier in the loop, that won't make it an IS loop.

I'm planning on replacing a bunch of old IS barriers with new ones. I'm in the processes of getting the part numbers of the instruments currently in use to confirm they are IS rated. However if the system was designed properly to begin with, all the instruments "should" be IS rated. Does this sound correct or is there more to it?

 

This is a two-part exercise.

You will need to verify that all the field instruments (including any such as series indicators installed in non-zoned areas but on the hazardous side of the barrier) do have relevant IS certification. This should be the case but don't count on it.

You will also need to check that the entity calculations for the new barrier/device installations are still compatible - in other words, the maximum voltage and current the barrier can deliver are less than the minimum safe voltage and current the device can withstand, and the total L and C values (including cable) for the connected circuit are less than the maximum the barrier is certified for.

Cheers,
Bruce.