Sierra Monitor Corporation TR-001 - Manual (Page 2)

Technical Reprint TR-001
Sierra Monitor Corp. 1991 Tarob Ct., Milpitas, California 95035 USA 408-262-6611, 800-727-4377 FAX: 408-262-9042
Visit our Web Site at: http://www.sierramonitor.com E-Mail:
[email protected]
GAS MONITORING OPTIONS
Gases are monitored with permanently installed (fixed) systems or portable instruments, or by taking samples for
evaluation in a laboratory. Portables and sampling are by their very nature only spot checks and are appropriate
only when the risk is extremely low or fixed instruments are not practical. As a general principle, areas where the
risk is sufficient to justify periodic monitoring with a portable instrument, warrant a fixed system.
Conventional Technology. Fixed gas monitoring systems historically have been reactive systems consisting of a
sensor and a controller. The sensor, which can be mounted remote to the controller, usually transmits an analog
signal proportional to the gas concentration. Principles of detection include catalytic bead, solid-
state/semiconductor, electrochemical and infrared.
Performance variables that should be considered for sensor performance include:
• Response speed
• Measurement range
• Resolution
• Interfering gases
• Operating range
• Temperature and humidity effects
• Sensor life span
• Ease and frequency of calibration
• Replacement cost
The gas monitoring system required depends upon the scope of the hazardous gas risk. For applications where the
risk is minor, a simple gas monitor that sounds an alarm when the concentration reaches the setpoint may meet the
need. Applications involving a higher risk generally require continuous output of gas concentration to a display,
printer or other indicating or control device. Sierra Monitor's analog gas sensor modules offer a continuous 4-20 mA
DC output and are available for a wide range of hazardous gases.
In applications with the highest level of risk or where the hazard is present throughout the facility, a smart gas
sensor module such as the IT Series and/or the Sentry Gas Risk Management System will meet the need. With
extensive diagnostic capability, flexible configuration, expandability, microprocessor controls, and the ability to
interface with plant-wide control systems, Sierra Monitor IT Series and Sentry Systems are the choice for plant-
wide monitoring systems.
System self-diagnostics on both the IT Series sensors and the Sentry controller and sensors help the user know that
the data they are receiving in reliable and accurate.
Gas exposure data analysis needs to be available to prove due diligence in hazardous gas risk management. This
data can be available either via preformatted reports available with the optional printer for Sentry or via a third party
HMI package resident on a computer. Serial communication and the MODBUS interface enable Sentry and IT
Series sensors to interface with the Human-Machine-Interface (HMI) package that can provide complete data
analysis and information on the operator's computer. Such information would include alarm status, gas
concentrations, alarm setpoints, fault alarms, and more. Hundreds of data points are available from Sentry via the
serial communications port.
Sentry’s ability to accept input from a wide variety of devices such as flame detectors, or other unique gas detectors
provides a complete hazard monitoring system to improve the safety management of the facility.