4-20 mA through EExi-barriers

K

Thread Starter

kishore

Vendor asked us to provide these barriers for 24VDC (2-wire) supply pressure transmitters for new project. Please clarify. Thanks in advance.
 
We are going to erect a new plant called Polyaluminium chloride. In this plant consultant asked us to provide 4-20 mA through EExi-barriers for 24VDC 2-wire pressure transmitters. What is these barriers?

Please clarify. Thanks in advance.
 
@Kishore,

Ex i barriers are used for intrinsically safe purpose.

these barriers limit the power/energy going to field such that no explosion occurs at specified conditions.

sun
 
B

Bruce Durdle

Ex i is used to prevent a low-power electrical circuit from igniting a flammable atmosphere. It relies on limiting the voltage and current levels applied to a circuit, and the energy that can be stored in it. The barrier is a component that contains (in its simplest form) zener diodes to limit voltage, and resistors and fuses to limit the current.

There are a LOT of implications of using Ex i systems, and simply adding barriers to a transmitter circuit will not be adequate - the transmitters and other components on the transmitter side of the barriers also need to be designed and certifies to meet specific requirements. There are also issues relating to site management.

I strongly suggest you check what credentials your consultants have for this sort of work, and talk to site management about all the related issues.

Cheers,
Bruce.
 
Hi,

I imagine that you specified "i" protection for your pressure transmitters which are in hazardous area. So, you need to connect the 4/20mA to a barrier (intrinsically safe interface) in a non hazardous area. The purpose of this barrier is restriction of electrical energy to the transmitter to prevent a potentially explosive atmosphere.

You have 3 levels of protection: "ia", "ib" and "ic".

In case of intrinsically safe installation, it will be additionally demonstrated that the entire loop satisfies the requirements of the intrinsically safe standard. For that, a calculation note will be provided for each loop type.

Bruno
 
Top