Gas
Sensor Technology
Sierra Monitor integrates extensive gas sensor technology with electronics expertise to offer a broad line of diffusion gas sensor modules for your specific application needs. Sierra Monitor sensor technology includes:
- Catalytic Bead Sensors for Combustible Gas
- Infrared Sensors for Combustibles
- Electrochemical Sensors for Oxygen and Toxic Gas
- Semiconductor Sensors for Combustibles and Ammonia
Catalytic Bead Sensors (5100-02-IT)
Catalytic bead sensors are used to monitor
combustible gases and are found in the Model 5100-02-IT gas detectors. The poison-resistant sensor provides reliable zero stability
and linear response to combustible gas over a wide temperature range.
The sensor consists of two alumina beads, each surrounding a platinum wire operating at approximately 450oC. One bead is passivated so it will not react with combustible gas. The other bead is catalyzed to promote a reaction with combustible gas. Effects of changes in ambient temperature and relative humidity are nullified by placing the two beads in separate legs of a Wheatstone bridge circuit. When the catalyzed bead reacts with combustible gas it heats up, which increases its resistance and, in turn, increases the output of the Wheatstone bridge circuit used as a sensor signal.
Electrochemical Sensors
Electrochemical sensors are fuel cell-like devices consisting of an anode, cathode, and electrolyte. The components of the cell are selected so a subject gas, allowed to diffuse into the cell, will cause a chemical reaction and generate a current. The cells are diffusion limited so the rate the gas enters the cell is solely dependent on the gas concentration. The current generated is proportional to the rate of consumption of the subject gas in the cell.
Sierra Monitor electrochemical sensors
provide improved reliability by allowing the gas to diffuse into the
sensor through a capillary port, rather than diffusing through membranes.
The result is an extremely stable sensor with very low temperature
and pressure coefficients and the capability to monitor gas as a percent
by volume (oxygen) and ppm (toxics)
Semiconductor
Sensors
Semiconductor sensors have a resistance in air that is affected by oxygen adsorbed on the surface of the sensor. Oxygen atoms capture electrons on the semiconductor surface, thereby increasing its resistance.
The sensors can be impregnated with dopants such that the sensor's resistance changes when specific gases displace the adsorbed oxygen.
Semiconductor sensors are simple and robust and widely used in domestic gas detectors but are not very specific to a particular gas as often required for industrial applications.
Infrared Sensors (5100-28-IT Combustible Gas Sensor Module)
Most combustible gases absorb infrared light energy at defined wavelengths, providing an adsorption signature for that gas. The principle of an infrared detector is based upon the adsorption of the infrared light at a specific wavelength as it passes through the gas. The more of the adsorbing gas that is present, the more light is adsorbed. Two light sources emite light of two different wavelengths through a gas sample. The beams are reflected back through the sample where the detector compares the signal strengths of the sample and reference beams and calculates the gas concentration by the light absorbed.