Engineering Documentation

Table Of Contents
Glossary
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Class 2 Power Source, Inherently Limited
An inherently limited Class 2 power source has some form of current-limiting
characteristic designed into the product. Sources of this type are often protected by a
current-limiting impedance or embedded fusible link, but other methods are also used.
As long as the current limiting is an integral part of the power supply, it will fall into this
category. Because of this built-in current-limiting characteristic, a circuit powered by
this type of source needs no further protection to qualify as a Class 2 circuit.
Class 2 Power Source, Not Inherently Limited
A Class 2 source that is not inherently limited does not have built-in current limiting
protection. At the time of installation, a current-limiting device must be installed
between the source and the loads. The most common current limiting device for this
application is a single fuse or integral transformer circuit breaker, which must be sized
so that the power available to the loads does not exceed 100 VA.
EIA
Electronic Industries Association.
Electromagnetic Interference (EMI)
Electrical noise induced in process wiring by electric or magnetic fields created by
power wiring, other process wiring, or electrical equipment.
Field Level Network (FLN)
Data communications link that passes information between an FLN device or devices
and an Automation Level Network (ALN) device.
IEEE
Institute of Electrical and Electronic Engineers.
IEEE Standard 802.3
Explains the basic functioning of the CSMA/CD (Carrier Sense Multiple Access with
Collision Detection) packet network with an exclusive focus on the ISO/IEC
(International Organization of Standardization and the International Electrotechnical
Commission).
Initiating Device Circuit (IDC)
Used in Protective Signaling Systems (that is, fire alarm and security systems) to
monitor alarm or supervisory sensing devices (manual stations, smoke detectors,
valve tamper switches, etc.).
Interoperability
Process that ensures that multiple nodes (from the same or different manufacturers)
can be integrated into a single network (LonWorks ® FLN) without custom
development.
Lay
Axial distance required for one cabled conductor to complete one revolution about the
axis around which it is cabled (for example, a cable lay of 2 inches (50.8 mm) is
equivalent to six twists per foot).