Mat Bagenski and Michelle Todd outline the benefits of encoders
Encoders are often needed for speed or position feedback in oil and gas applications, and must be designed and certified to the appropriate hazardous area rating.
The conditions under which exposure to the hazardous agent is expected significantly affect the encoder rating requirement.
The most stringent rating requirements are where an ignitable agent will be present continuously or intermittently under normal operating conditions – classified as Division 1 (UL), Zone 0, or Zone 1(EU and IEC). If an ignitable agent exists rarely or only under abnormal operating conditions, it is classified as Division 2 or Zone 2.
One protection method which can be used for this latter classification is referred to as non-incendive (Division 2) or non-sparking (Zone 2); slightly different terminology but in essence it encompasses the same methodology.
A certified encoder with this rating is evaluated to assure that no sparking or hot surfaces will occur when it is properly installed and operated within the manufacturer’s specified limits.
No additional equipment is required. Nonincendive products used in the US must be installed using wiring methods specified per NFPA 70, 501.10(B) (National Electric Code) with similar requirements in Canada. Non-sparking devices must be installed as specified in IEC 60079-15, Chapter 7.
Using a more stringent area rating is allowed and in the past encoders for Division 2 or Zone 2 typically involved installing encoders certified for the more rigorous Division 1 or Zone 0, or Zone 1 environments.
Even though they were installed in a less hazardous area, these encoders must follow the installation requirements for a Division 1, Zone 0 or Zone 1 environment. This includes special enclosures, more complicated installation techniques and, sometimes, additional associated apparatuses. For example, an intrinsically safe protection method requires an encoder with special electronics and the use of a barrier to limit the power supplied to it, which can affect the overall performance of an application.
Today, engineers have a larger selection of encoders available specifically designed and certified to operate safely in Division 2 or Zone 2 environments.
These encoders offer several benefits including simpler installation, no need for an associated apparatus (such as a barrier) and no restriction of energy to the hazardous location.
These encoders also take up less space in the application and are often less costly than encoders designed for more hazardous environments. This can all add up to operational savings from less costly equipment and less time spent on installation and system maintenance.
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Mat Bagenski and Michelle Todd are with BEI Sensors is based in Goleta, CA, USA. www.beisensors.com