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What are Barriers and Isolators and why are they used in industry?

In Instrumentation, safety plays a very important role while supplying power to the field devices in hazardous areas. Protecting the system against any fault which has occurred in the field is also very important. If the fault is not handled properly, then it can damage the system which costs million of dollars in many cases. 
For the protection of the system as well as maintaining the proper level of power to the field Instruments, barriers and isolators In this article we will see the difference between a barrier and an isolator.

1. Barrier 

The barrier is used to limit the energy going to the field. In the case of the Intrinsic Safe system, limiting energy to the field is very important. Barriers play a very important role in Intrinsic Safe circuits.

The barrier has a fuse, current limiting resistor as well as a Zener diode to limit the voltage. 

The fuse burns out in case of high current flow, the resistor maintains the amount of the current going to the field, and the Zener diode restricts the fault voltage. 

Barriers are used for areas with potential hazards of blast or explosion due to sparks. Hence, limiting the energy to the field will help to avoid any such conditions occurring due to spark.

The barrier will limit energy which will not create a spark in any case. The barrier should only be used when the earthing system is perfect.

As seen in the figure, an MTL7728P+ Shunt-diode safety barrier is shown. Also, the figure on it depicts the use of a resistor, a fuse, and a Zener diode.

Good earthing is a must requirement for using a barrier. Also, when the voltage level increases, the fuse will blow out and the Zener diode barrier will need replacement. There is a certain amount of voltage drop because of the circuit too.

2. Isolators 

The Isolators are used to isolate the field Instruments from the system. And Isolators are used to remove the ground loops forming in analog circuits.

Ground loops form when there is more than 1 ground connection in a loop. Due to this the ground current starts flowing in the loop and disrupts the main signal. 

The construction of an isolator consists of one main component which is an Opto Isolator or a transformer in rare cases. This physically isolates the loops of the field as well as the system. 

Isolators are also used to isolate the Instrumentation system which is working on 24 VDC or even less from the electrical system or from any unwanted spike in electrical voltage in the circuit. The unwanted spike can be due to lightning or high loads.

Magnetic isolation, optical isolation as well as capacitive isolation methods are used to isolate the field signal from the system. The figure shows an isolator of MTL make and model number 5532.

• The cost of a normal Zener barrier is much less compared to the isolators. This is because the isolators have additional circuit components also.

• Nowadays isolated barriers are available in the market which does the purpose of both isolators as well as barriers.
• The isolated barriers are widely used in Emergency Shutdown Systems because this system is one of the most critical and important systems of the plant.

EndNote

I hope now you have an idea about What are Barriers and Isolators and why are they used in the industry?