How Limit Switches Can Stop Machines from
Going Boom
By Tom Werner
Senior Product Marketing Manager,
Honeywell Sensing and Productivity Solutions
Safety is one of the top criteria when selecting a limit switch for
hazardous location environments. In many cases, these switches
have to operate in the presence of explosive fumes or gases, in
dirty or dust-��lled environments, in remote parts of the world and
around extremely harsh chemicals that breakdown electronics
very quickly. These applications, including oil & gas drilling rigs,
agricultural environments filled with pesticides and chemicals
and outdoor locations with extreme weather conditions, all pose
dangers to personnel, materials and equipment.
As an example, a hazardous area may have an atmosphere that
could potentially ignite, burn or explode due to a spark caused
by electrical equipment. This means the components selected for
these applications need to be extremely safe as well as reliable,
durable and long lasting.
To withstand these harsh environments, the limit switches must
comply with explosion-proof switching requirements to ensure
the safety of personnel, equipment and the environment. For
example, Honeywell Sensing and Productivity Solution’s MICRO
SWITCH™ hazardous location switches can reduce the risk
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of explosion by containing sparks and other electrical events
inside the sealed switch body. Under normal conditions, these
sparks or electrical events typically do not pose a lot of danger;
however, in environments where there are substances that can
potentially ignite or explode, sparking and arcing from electrical
components is potentially dangerous. The MICRO SWITCH™
switches provide protection through a sealed switch cavity, which
incorporates mechanical threads that contain or cool flames,
minimizing the risk to the surrounding environment.
Hazardous location limit switches are used in a variety of
industrial applications, ranging from mud pumps, valve
positioning and pig position detectors to gate/door monitoring
in grain conveyors and grain gates. Here are several examples
of how these switches are used in hazardous or explosive
environments.
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Oil & Gas Drilling: Mud Pumps, Blow-out
Preventers (BOP), Drilling Rigs, Pipeline Pigs
Mud pumps are used in oil and gas
drilling applications to circulate the
fluid that provides lubrication for the
drill while pressurizing the bore hole
to prevent well cavitations. These
pumps use switches as pump
stroke counters. These switches
can be used to send a signal to
cancel out the noise generated
from the pump in order to gather
sonic data to model the geographic
formation of the oil well and to
monitor the fluid, ensuring the
safety of personnel and equipment.
Blow-out preventers (BOP) and
BOP control units are used to
seal, control and monitor erratic
pressures and uncontrolled flow that can occur during oil and
gas drilling. These critical pieces of equipment are vital for
the safety of the crew, rig and environment and to maintain
the integrity of the well. If there is any kind of disruption, an
emergency system can disconnect the rig from the well, which
automatically triggers a switch to close the BOP and choke
valves.
Position switches are also implemented in heavy-duty drilling rigs
where they are used to detect vertical or rotary position when a
new drill tube is moved into place. If the position measurement
is inaccurate it could damage the drill, drilling equipment and/
or well, resulting in tens to hundreds of thousands of dollars in
damage. These switches need to be extremely robust, offering
environmental sealing, high operating temperatures and high
accuracy.
Similarly, switches used in pipeline pigs, which are used to clean
and inspect the integrity of a pipeline without stopping the flow
of the fluid, need to be highly reliable and accurate. To detect
when a pig has passed through a particular section of the pipe,
these switches are used to trigger an electrical signal along the
pipeline based on the indicators. These pipelines can be found
in remote locations on land and under water.
Grain Conveyor/Grain Gates
Conveyors are often used
in enclosed spaces in grain
processing and handling facilities.
These conveyors, which require
complex systems for control
and safety, use limit switches for
position detection of equipment and
materials.
Limit switches also can be used in
grain gates that operate as valves
in the grain storage and handling
industry. These doors open or close
and control the flow of grain. In this
application, the switch detects the
gate position, which is relayed to
the central control unit, whereby the
signal is used as process control
or secondary indication. For these agricultural applications, the
switches need to be sealed and be weather tight to keep out the
grain particulates.
Painting Booths
In painting booths, which are used to control the environment
for paint applications, including machinery and component
manufacturing, these environments must be dust and debris free
to reduce downtime and waste. A limit switch is used to indicate
the position of the door in the painting booth. The painting
process cannot start until the door is fully shut. These switches
require sealed, weather tight enclosures to keep paint and/or
debris particulates from interfering with their operation.