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

Catalytic bead sensors are used to monitor combustible gases and are found in the Model 410X-02 series sensor modules. 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 450^oC. 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.

 

 

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. The sensor compares the energy emitted by the light source to that received by the detector resulting in the amount of light adsorbed by the gas.