Sierra Monitor Corporation Gas Sensor - Manual (Page 2)

© 1998 by Sierra Monitor Corporation
Sierra Monitor Corporation 1991 Tarob Court Milpitas, CA 95035 USA (408) 262-6611 (800) 727-4377 Fax: (408) 262-9042
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Smart Sensors
Smart or intelligent sensors improve the
communication from the sensor to
controller and improve the reliability of
sensor data by better signal processing.
Smart sensors use digital signals rather
than analog signals to transmit to the
controller. Digital signals provide the
opportunity for greater diagnostics and
data checking.
Smart sensor diagnostics involve
continuous checks to identify out-of-
bounds system operating criteria. The
sensor accesses operating
characteristics, checks the operating
voltage, and continuously verifies that the
dynamic range of the sensor provides
adequate resolution. Warning messages
from the sensor identify items such as
low sensor sensitivity and low battery.
In addition, some smart sensors can deal
with detection of intangible properties
such as softness, freshness, sweetness, or aroma. New
smart sensors in the biological, medical and
pharmaceutical world can detect cholesterol and lipids.
In the industrial sector, smart sensors have enabled the
plant operator to obtain more reliable data.
Sensor Systems
But, more reliable data is still just waiting to be converted
into information. Sensor systems have significantly
improved operator efficiency by effectively and quickly
converting large volumes of data into useful information.
The operator needs input from a variety of sensors and
locations to make knowledgeable decisions. Today’s
more powerful sensor systems have the following
characteristics:
• Accepts input form various sensors (and various
manufactures);
• Provides local display of sensor readings;
• Allows for non-intrusive sensor calibration;
• Provides relays for local alarm action;
• Follows user-defined alarm strategy;
• Accepts feedback signals from final control
elements;
• Has independent battery backup;
• Is a low-cost link to the control room;
• Provides centralized monitoring.
Distributed intelligence is central to proper sensor system
design philosophy. Since the field controllers are
intelligent with the capability to implement alarm logic
and operate independently of the host computer,
interrupted communication with host computer does not
hamper field operation. In addition, sensor systems
provide the user with clear, understandable data that
enables the operator to analyze the situation quickly
and take the required action.
A sensor system not only provides the best features of
local control and centralized monitoring, but also
systemizes the entire monitoring process. The system
provides plant personnel with sufficient, reliable
information to ensure that decisions are made with
maximum knowledge of the current situation. Sensor
systems accept a wide range of sensor inputs, including
those with non-linear signals. The remote controller
conditions to signals, compares with data from various
inputs, and transmits the data to the control room.
Within the I/O controller, the input values are used for
equation processing, alarming, control, event sequencing,
and more. Complex control and logic algorithms and
parameters for each channel can be constructed and
modified by the operator.
Generally, all data from the system is accessible from
the control room via simple twisted pair cabling, telephone
lines, or radio signals. In the control room, the operator
can access data from a variety of sensors. Using PC-
based software package combined with an intelligent
remote controller provides the user with the flexibility to
configure sensor system inputs, outputs, and data
acquisition to meet the plant’s specific needs. The result
is greater visibility of plant operations, allowing better
decision to be made.
Figure 2. Typical sensor system at a wellhead accepts input from a variety of
sensors concerning safety, environment, process and security; performs
automatic control and alarm functions; and communciations to a central control
facility.