Application Note

Application Note
Tracking down problems within
a process loop can be a difficult
challenge in the best of environ-
ments. Doing so in an area that
has the potential for explosion
takes the degree of difficulty to
another level – one where the
technician needs proper training
and equipment. This article will
demonstrate the practical applica-
tion of loop calibrators designed
to troubleshoot process loops in
intrinsically safe environments.
What is “intrinsically
safe?”
Intrinsic safety is a protection
standard employed in potentially
explosive atmospheres. Devices
certified as “intrinsically safe”
are designed to be unable to
release sufficient energy, by
either thermal or electrical
means, to cause ignition of
flammable material (gas, dust/
particulates).
Intrinsically safe standards
apply to all equipment that can
create one or more of a range
of defined potential explosion
sources:
•
Electrical sparks
•
Electrical arcs
•
Flames
•
Hot surfaces
•
Static electricity
•
Electromagnetic radiation
•
Chemical reactions
•
Mechanical impact
•
Mechanical friction
•
Compression ignition
•
Acoustic energy
•
Ionizing radiation
Intrinsic safety is particularly
important for technicians
working in industries like petro-
chemical and pharmaceutical,
around bulk materials such as
grain, mining, or any environ-
ment where explosive gases are
present.
The importance of safety in
these environments can’t be
stressed enough. It takes a very
small amount of energy to cause
an ignition; e.g., a mixture of
hydrogen in air requires only
2O uJ of energy. The proper
practices and tools will minimize
the inherent risk involved in
working around these hazards.
Intrinsically safe loop
calibration
To conduct loop calibrations in
potentially explosive environ-
ments, you need a loop calibrator
that is certified as intrinsically
safe. Intrinsically safe loop cali-
brators, such as the Fluke 707Ex,
must be certified in accordance
Troubleshooting process
loops in potentially
explosive atmospheres
F r o m t h e F l u k e D i g i t a l L i b r a r y @ w w w . f l u k e . c o m / l i b r a r y
with the European ATEX (“Atmo-
sphères Explosibles,” French for
explosive atmospheres) directive
(Ex II 2 G Ex ia IIC T4) in Zones 1
and 2 for use in Europe and NEC
500; N.I. Class 1, Division 2 areas
Group A-D for use in the U.S.
In addition to an intrinsically
safe loop calibrator, strict adher-
ence to calibration procedures is
recommended, including:
Lock out: Make sure the system
is shut down and other work-
ers are notified that a potentially
dangerous operation will be tak-
ing place.
Tape off area: Tape the work
area off to prevent workers from
entering with potentially dan-
gerous electrical devices (cell
phones, handheld computers,
non-intrinsically safe tools).
Purge or vent the systems:
Safely purge or vent the system
to remove any gases that may
remain.
Use a gas detector: In an envi-
ronment where explosive gas
may be present, the use of a gas
detector is a prudent step before
starting a loop calibration. Gas
“sniffers” are available for a wide
variety of applications and from
handheld to larger, carted models.
Calibrate: Perform your calibra-
tion using an intrinsically safe
loop calibrator.
Clean up and reactivate: At the
conclusion of calibration, reverse
the process and reactivate the
system.
Loop calibration
The 707Ex Loop Calibrator has
the ability to replace the power
source in a current loop so you
can power and read a transmitter
at the same time without carry-
ing a digital multimeter (DMM).