Electric pressure sensors use the same phenomena as the mechanical stress sensors - a change in longitudinal extension is processed into a change in resistance or electric capacity of the sensor. Sensors with membrane construction are usually used to pressure measurements. The electric signal
of the sensor is a selected electric parameter of the membrane itself, or of the strain gauge attached to the membrane. Semiconductor pres- sure sensors are generally used, in the form of integrated devices. The voltage at the output of the integrated pressure sensor is proportional to the measured value p. The material used for semiconductor sensors is p-type silicon, and sometimes germanium. The pressure sensors are designed to measure absolute pressure or differential pressure. In the case of absolute pressure measurement, one side of the sensor membrane is subjected to a strong sub pressure, and in the ideal case, to vacuum pressure. Pressure sensors may be otherwise divided up according to the criterion of measuring range.
There are sub pressure sensors (p < 1 bar), standard pressure sensors (p close to 1 bar), and high-pressure sensors (p > 2 bar). Semiconductor pressure sensors, like semiconductor strain gauges, demonstrate a strong dependence of their processing characteristic on temperature. For silicon pressure sensors, the change in strain gauge factor kt is estimated to be 10% for ∆T = 1°C. In a measuring circuit with semiconductor pressure sensors, the compensation of temperature influence should always be taken into consideration.
Some types of integrated semiconductor strain gauges, designed to measure stress or pressure, contain a strain gauge and a thermosensitive device in one structure. The purpose of the thermosensitive device is internal compensation of temperature effect in the integrated pressure sensor. The second variant for a temperature compensation is to establish pins on the pressure sensor package in order to connect the thermosensitive device. The latter solution allows construction of a measuring circuit with additional compensation of temperature influence. A pressure sensor with internal thermal compensation indicates the dependence of output voltage on temperature, determined by a coefficient value of approximately 0.2% per degree Celsius. A considerable number of semiconductor pressure sensors are calibrated by the manufacturer and sold together with a certificate of parameters, or even with an individual sensor characteristic. Certainly, this makes the price of the sensor higher.
For example, the catalog of a series of pressure sensors manufactured by NeXt Sensors-Data Instruments numbers 127 types of semiconductor integrated sensors. Some manufacturers of semiconductor pressure sensors (e.g., Data Instruments, Honeywell) plan to introduce digital sensors to the market. The output voltage of integrated pressure sensors is usually on the order of millivolts, and it is symmetric to the ground. The recommended measuring circuit for such sensors is the differential amplifier. Integrated converters indicate a high offset voltage, comparable to the utilization signal. The voltage must be compensated in the measurement circuit. Semiconductor sensors are characterized by a great value of the overload factor. For the XCX01DNC sensor, the nondestructive test overload factor ptest/prange equals 5, and the destructive load factor equals 20.
