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Hazardous Location Encoder Overview

Encoders are used in hazardous areas where flammable liquids, vapors, gases or combustible dusts may exist. There are several methods of designing encoders for hazardous environments and all have varying degrees of Zone and Class & Division ratings. Below are the major categories.

Intrinsically Safe Encoders

Intrinsically Safe BarrierA common protection method is intrinsic safety (Ex ia). Intrinsically Safe rated encoders can be approved for use in either IEC Zone 0 or NEC500 Class 1 Division 1. Intrinsically safe encoders are used in conjunction with an energy limiting electronic device commonly known as an IS Barrier. This device, in Zener, opto-isolated or galvanic, limits the energy allowed in the circuit such that any arcs or sparks in this encoder has insufficient energy to ignite a vapor.

Flame Proof Encoders

AX65 ThumbnailA Flame proof (Ex D) design can withstand an internal explosion and provide relief of the external pressure via flame gap(s) such as the labyrinth created by threaded fittings or machined flanges. The escaping (hot) gases must sufficiently cool down along the escape path that by the time they reach the outside of the encoder enclosure not to be a source of ignition of the outside, potentially ignitable surroundings. Both optical and magnetic encoders are available in one piece designs. Flame proof encoders are approved for use in either IEC Zone 1 or NEC505 Class 1 Zone 1.

Encapsulated Encoders

EN44 Explosion Proof Encoder with Encapsulated ElectronicsDevices utilizing encapsulation have the electronics encased in a resin type material to isolate them from the surrounding atmosphere. Encapsulted encoders are approved for use in either IEC Zone 1 or NEC505 Class 1 Zone 1. 
 

Non Incendiary Encoders

Equipment is non-incendiary or non-sparking and approved for IEC Zone 2 and NEC500 Class 1 Division 2.

Hazardous Area Classifications

A multitude of options exist for applying explosion proof encoders successfully in hazardous locations. Each has its own pros and cons, and ultimately the end user or design engineer must factor several things into account such as level requirement, electrical requirements, IP ratings and physical size and total cost of ownership.

 

European and IEC Classification

North American Classification

Definition of Zone

Zone 0 (Gases / Vapors) Class l Division 1 (Gases) An area in which an explosive mixture is continuously present or present for long periods
Zone 1 (Gases / Vapors) Class l Division 1 (Gases) An area in which an explosive mixture is likely to occur in normal operation
Zone 2 (Gases / Vapors) Class l Division 2 (Gases) An area in which an explosive mixture is not likely to occur in normal operation and if it occurs will exist only for a short time
Zone 20 (Dusts) Class II Division 1 (Dusts) An area in which an explosive mixture is continuously present or present for long periods
Zone 21 (Dusts) Class II Division 1 (Dusts) An area in which an explosive mixture is likely to occur in normal operation
Zone 22 (Dusts) Class II Division 2 (Dusts) An area in which an explosive mixture is not likely to occur in normal operation and if it occurs will exist only for a short time

Popular Hazardous Area and Explosion Proof Encoders

ISD37 Intrinsically Safe EncoderEN44 Zone 1 Incremental EncoderAX65 Explosion Proof Encoder Absolute