Tech Briefs Magazine - May 2023 - Sensor-11

TECHNOLOGY LEADERS Sensors
How to Engineer Intrinsically Safe
Hazardous Duty Wireless Sensors
A
n apparatus such as a wireless
sensor used in a hazardous location
must be designed and certified
to meet the required safety
standards. Those standards are amplified
when the environment and work already
deemed inherently hazardous duty is
done in areas where explosive (Ex) atmospheres
are anywhere from always to only
rarely present.
Risks from Explosive Atmospheres are in
Many Industries
It's easy to consider explosive atmospheres
in the oil and gas industry
as hazardous locations for electrical
equipment - at petrochemical and
refining facilities, field and offshore
drilling operations, and gas stations.
But explosive atmospheres with flammable
and combustible gases, vapors,
dust, powders, and fibers can be present
in other industrial applications -
such as chemical production, pharmaceutical
and cosmetics manufacturing,
food processing, power generation,
mining, construction, and architectural
woodworking.
By law and good sense, everything and
everyone must be safeguarded and certified
according to the safety standards for
these hazardous locations. What's the
risk? One tiny spark or overheated device
could ignite an explosion, causing
damage, injury, or even loss of life.
Engineers Make Critical Design Decisions
For operations in explosive or potentially
explosive atmospheres, engineers
must ensure each process, system, and
apparatus meets or exceeds safety regulations
from design to production to installation
and operation. Engineers can
use several protection methods against
explosive atmospheres to create safe hazardous
duty sensors.
* Some methods involve electronics segregation
like encapsulating electronics
in epoxy, covering electronics in
non-flammable oil or powder, or sealing
electronics in a vacuum chamber.
* Another method is to use an explosion-proof
enclosure to confine any
explosion inside its robust, rugged
housing.
* The intrinsic safety method limits an
apparatus's electrical and thermal energy
by the laws of physics from creating
a spark or hot spot sufficient to
ignite an explosion during normal operation
and fault conditions anywhere
within the circuitry.
These methods aren't mutually exclusive,
but in our view, intrinsic safety is the
gold standard.
Whatever
the protection
method,
an engineer's job is to plan and design
products using safety standards like
those of the International Electrotechnical
Commission (IEC). The IEC System
for Certification to Standards Relating
to Equipment for Use in Explosive Atmospheres
(IECEx) ensures engineers,
manufacturers, and equipment meet
strict safety requirements. We chose
IECEx as the standard system and epoxy
encapsulation to design our intrinsically
safe ALTA-ISX® Sensors.
IECEx Certification for Intrinsically Safe
Sensors
To be IECEx-certified, sensors must
meet multiple design standards and a
production standard. The design standards
include the general IEC 60079-0
standard and at least one protection
method-dependent standard such as
IEC 60079-11 for intrinsic safety. The
production standard is the International
Organization for Standardization
(ISO)/IEC 80079-34, similar to ISO
9001 with quality management system
additions for hazardous locations.
Engineers can purchase the IECEx
standards to guide design and conformity.
Then, they can hire a third-party
IECEx Certification Body (ExCB) to test
and verify the design against the standards.
The ExCB requires you to submit
design information, such as schematics,
Gerber files, and a bill of materials
(BOM); and production information,
such as quality management system documents
for manufacturers.
Figure 1. Petrochemical and refining facilities are a typical use-case for intrinsically safe sensors.
(Image: Monnit)
Sensor Technology, May 2023
www.techbriefs.com
The designer should know that an
IECEx production certificate locks the
design documents down to the make and
model of each surface mount resistor
identified in the BOM. The ExCB will also
need to review and approve a safety manual
outlining the sensor's safe installation,
use, and maintenance requirements.
Being IECEx-certified allows you to sell
sensors internationally without re-testing
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Tech Briefs Magazine - May 2023

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