Sierra Monitor Corporation 1991 Tarob Court Milpitas, CA 95035 USA (408) 262-6611 (800) 727-4377 Fax: (408) 262-9042
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S
ensors are in our home,
transportation, and workplace
affect our safety, environment, and
productivity. You awoke this
morning in a warm room because a
sensor monitored the room
temperature. The car you drove to
work has sensors for temperature,
oxygen emissions, and more. Its
control panels are covered with
lights, gauges, and switches. Yet, conflicting data,
possible burned-out lights, and trying to read too many
gauges, lights and indicators repidly can make your job
difficult and prone to problems.
Sensors are the primary building blocks that provide the
vital function of acquiring data and transmitting it to
human operators. Just as sensors have permitted a
simplified way of flying commercial airlines, sensors
provide the necessary information for efficient and
effective operation of every process and facility.
Sensors must operate under diverse conditions, 24 hours
a day, 365 days a year. Some sensors are designed to
operate in extreme temperatures, pressures, flow, and
corrosive or hazardous conditions. Sensors development
incorporates specific industry needs, including hardened
sensors that are resistant to specific environmental
conditions, miniaturized sensors, disposable sensors,
and sensor systems. Purchasers of sensors must
consider the variables of their specific application. As
an example, purchasers of gas detection sensors must
consider the following when selecting a sensor for their
application: speed of response, measurement range,
accuracy, resolution, interfering gases, operating range
(temperature, humidity, pressure), temperature and
humidity effects, sensor life, ease of calibration,
calibration frequency, and replacement cost.
Simple Sensors
Historically, sensors have been simple devices capable
of monitoring a specific variable. The human operator
reviews the data generated by these simple sensors and
determines what action needs to be taken. Limitations
include:
• All intelligence resides in the sensor controller;
• Communication from sensor to controller is
analog;
• Controllers typically are dedicated to specific
sensor types;
• Multiple sensors require multiple controllers;
• Calibration requires intrusive manual
adjustments of transmitters and a corresponding
adjustment of controllers.
Often, because of these limitations, operating decisions
are based on the input from only a few devices,
concerning a few parameters. Simple sensors generate
data but not information. The operator might be
concerned about data reliability if the sensor was overdue
for calibration, or if the data from a sensor was outside
the norm. The process can end in disaster due to
inaccurate data because of a burned-out bulb or a stuck
needle on a gauge.
Technical Reprint TR-004
SENSORS: SIMPLE TO SMART TO SYSTEMS
PC-based software plus an
intelligent remote controller
provide the flexibility to
configure sensor system
inputs, outputs, and data
acquisition to a plant’s
specific needs. The result
is greater visibility of plant
operations, allowing better
decisions to be made.
Figure 1. Typical field-mounted intelligent controller connected to
PC-based DCS.
(2 pages)
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