Ex-Hazardous Areas - Fluke 725Ex Calibration Manual

725Ex
Calibration Manual

Ex-Hazardous Areas

An Ex-hazardous area as used in this manual refers to an area made hazardous by the
potential presence of flammable or explosive vapors. These areas are also referred to as
hazardous locations, see NFPA 70 Article 500 or CSA C22.1 Section 18.
The Model 725Ex Multifunction Calibrator has been designed for use in Ex-hazardous
areas. These are areas where potentially flammable or explosive vapors may occur.
These areas are referred to as hazardous (classified) locations in the United States, as
Hazardous Locations in Canada, as Potentially Explosive Atmospheres in Europe and as
Explosive Gas Atmospheres by most of the rest of the world. The Calibrator is designed
as intrinsically safe. This means that connecting the Calibrator to equipment that is used
within intrinsically safe circuits will not cause an ignition-capable arc as long as the
entity parameters are suitably matched.
The Calibrator has two sets of parameters. The Vmax and Imax parameters show the
maximum voltage and maximum current that may be connected to the Calibrator
terminals without compromising the intrinsic safety. The voltage and current will
generally come from intrinsic safety barriers that provide power to the field equipment
such as transmitters and positioners (I/P devices). These barriers are identified with a
maximum open circuit voltage parameter (Voc) and a maximum short circuit current
parameter (Isc). The matching criterion requires that Voc of the barrier not exceed 30 V
and Isc not exceed 100 mA.
The Calibrator will itself be a source of voltage and current. Each set of terminals has a
Voc and an Isc rating as shown on Fluke 725Ex CCD. When connecting terminals to
other equipment, the Vmax and Imax ratings on the other equipment must exceed the Voc
and Isc ratings for the terminals connected to on the 725Ex Calibrator.
In addition to matching voltage and current entity parameters, it is also necessary to
verify that capacitance and inductance has not been exceeded. Again, Fluke 725Ex CCD
identifies the maximum capacitance (Ca) and maximum inductance (La) that is permitted
based either on the intrinsic safety barrier ratings or on the Calibrator ratings for the
specific terminals used. As an example, Fluke 725Ex CCD explains that the capacitance
of each unit connected in the circuit (Ci) plus the capacitance of the cable in the circuit
must not exceed the maximum allowed capacitance (Ca). Similarly for inductance in the
intrinsically safe circuit.
When connecting the Calibrator into a powered circuit, i.e. when the circuit is powered
by an intrinsic safety barrier, then the maximum circuit voltage used for the entity
parameter evaluation will be the higher of either the Calibrator Voc or of the barrier Voc.
The maximum current will be the sum of the Calibrator Isc and the barrier Isc. In this
case, the maximum allowed inductance (La) will be reduced. This value will have to be
determined using the ignition curves found in standards such as CSA C22.2 No. 157 or
UL 913.
For additional information about Ex-hazardous areas, refer to ANSI/ISA-12.01.01-1999
Definitions and Information Pertaining to Electrical Instruments in Hazardous
(Classified) Locations and to ANSI/ISA-RP12.06.01-2003 Recommended Practice for
Wiring Methods for Hazardous (Classified) Locations Instrumentation Part 1: Intrinsic
Safety.
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