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An oxygen sensor (or lambda sensor, where lambda refers to air–fuel equivalence ratio, usually denoted by λ) is an electronic device that measures the proportion of oxygen (O2) in the gas or liquid being analysed. It was developed by Robert Bosch GmbH during the late 1960s under the supervision of Dr. Günter Bauman. The original sensing element is made with a thimble-shaped zirconia ceramic coated on both the exhaust and reference sides with a thin layer of platinum and comes in both heated and unheated forms. The planar-style sensor entered the market in 1990 and significantly reduced the mass of the ceramic sensing element, as well as incorporating the heater within the ceramic structure. This resulted in a sensor that started sooner and responded faster. The most common application is to measure the exhaust-gas concentration of oxygen for internal combustion engines in automobiles and other vehicles in order to calculate and, if required, dynamically adjust the air-fuel ratio so that catalytic converters can work optimally, and also determine whether the converter is performing properly or not. An oxygen sensor will typically generate up to about 0.9 volt when the fuel mixture is rich and there is little unburned oxygen in the exhaust. Scientists use oxygen sensors to measure respiration or production of oxygen and use a different approach. Oxygen sensors are used in oxygen analyzers, which find extensive use in medical applications such as anesthesia monitors, respirators and oxygen concentrators.

A pressure sensor is a device for pressure measurement of gases or liquids. Pressure is an expression of the force required to stop a fluid from expanding, and is usually stated in terms of force per unit area. A pressure sensor usually acts as a transducer; it generates a signal as a function of the pressure imposed. For the purposes of this article, such a signal is electrical. Pressure sensors are used for control and monitoring in thousands of everyday applications. Pressure sensors can also be used to indirectly measure other variables such as fluid/gas flow, speed, water level, and altitude. Pressure sensors can alternatively be called pressure transducers, pressure transmitters, pressure senders, pressure indicators, piezometers and manometers, among other names. Pressure sensors can vary drastically in technology, design, performance, application suitability and cost. A conservative estimate would be that there may be over 50 technologies and at least 300 companies making pressure sensors worldwide. There is also a category of pressure sensors that are designed to measure in a dynamic mode for capturing very high speed changes in pressure. Example applications for this type of sensor would be in the measuring of combustion pressure in an engine cylinder or in a gas turbine. These sensors are commonly manufactured out of piezoelectric materials such as quartz.

The intake air pressure sensor is connected to the intake manifold by a vacuum tube. With the different speed loads of the engine, it senses the vacuum change in the intake manifold, and then converts the change of the internal resistance of the sensor is converted into a voltage signal for the ECU to correct the fuel injection amount and ignition timing angle. In the EFI engine, the intake pressure sensor is used to detect the intake air amount, which is called D-type injection system (speed density type). The intake air pressure sensor detects the intake air volume not directly like the intake air flow sensor, but indirectly. At the same time, it is also affected by many factors. Therefore, in the inspection and maintenance, there are many places that are different from the intake air flow of the quantity sensor, and the resulting faults also have its particularity. The intake pressure sensor detects the absolute pressure of the intake manifold behind the throttle valve. It detects the change of the absolute pressure in the manifold according to the engine speed and load, and then converts it into a signal voltage and sends it to the engine control unit. The ECU controls the basic fuel injection amount according to the magnitude of this signal voltage. There are many types of intake pressure sensors, such as varistor type and capacitive type. Because the varistor type has the advantages of fast response time, high detection accuracy, small size and flexible installation, it is widely used in D-type injection systems.