Sensor Technologies - Temperature Sensor

Temperature sensors are used for two purposes: The first is as a warning system, typically on obsolete oxidation-only catalytic converters. The function of the sensor is to warn of temperature excursions above the safe operating temperature of the catalytic converter. However, modern catalytic converters are not as susceptible to temperature damage. Many modern three-way Platinum-based converters are able to handle temperatures of 900 degrees C sustained, while many modern three-way Palladium-based converters are able to handle temperatures of 925 degrees C sustained. Temperature sensors are also used to monitor the temperature rise over the catalytic converter core.

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Sensor Technologies - Oxygen Sensor

Oxygen sensors are part of the closed loop fuel feedback control system, associated with modern three-way catalyst emission control systems on gasoline engines. The closed loop fuel feedback control system is responsible for controlling the air/fuel ratio of the catalytic converter feed gas. During the closed loop operation, the electronic control module (ECM) keeps the air/fuel ratio adjusted to around the ideal 14.7 to 1 ratio. Signal from the oxygen sensor is used to determine the exact concentration of oxygen in the exhaust stream. From this signal, the ECM determines whether the mixture is richer or leaner than the ideal 14.7 to 1 air/fuel ratio. If the air/fuel ratio deviates from its preprogrammed swings, catalyst efficiency decreases dramatically, especially for NOx reduction. The oxygen sensor informs the ECM of needed adjustments to injector duration based on exhaust conditions. After adjustments are made, the oxygen sensor monitors the correction accuracy and informs the ECM of additional adjustments. The oxygen sensor is also an integral part of the onboard diagnostic (OBD) system which monitors the proper functioning of the emission control system of the vehicle. If the sensor detects oxygen content of the exhaust that is outside the specified range of the engine calibration, it will trigger the engine light to come on in the instrument cluster.

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Sensor Technologies - NOx Sensor

NOx sensors represent state of the art technology that can be applied to gasoline lean burn engines as part of a broader engine control or diagnostic system used to insure proper operation of the NOx emission control system. These sensors can be incorporated independent of the NOx emission control technology used on the vehicle and their function is primarily to monitor the NOx conversion efficiency of the catalyst. The sensors can work as part of a feedback loop to the control unit on the emissions system to make real time adjustments and optimize NOx conversion. The principle of operation of one type of NOx sensor is based on proven solid electrolyte technology developed for oxygen sensors. The dual chamber zirconia sensing element and electro-chemical pumps work in conjunction with precious metal catalyst electrodes to control the oxygen concentration within the sensor and convert the NOx to nitrogen. The sensor sends output signals in volts that are directly proportional to ppm NOx concentration. The sensors can be incorporated upstream and downstream of the catalyst, for example, to provide a feedback control loop to the ECU of the emissions system. The ECU can than make adjustments to optimize NOx conversion performance. In the case of SCR technology, feedback can also be provided to the urea dosing system whereas in the case of lean NOx trap catalysts, a feedback loop could signal the regeneration of the trap.

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