A novel electronic PS pressure sensor

Overview

PS pressure sensor is a semiconductor membrane structure made of electronic pressure sensor, which will air pressure the physical quantity shift into electrical signals, and capable of high precision, linear to detect pressure changes.

It was launched in recent years the company Matsushita Electric works of new products.

As early as 1954 United States c.s.smith first confirmed the semiconductor piezoelectric resistance effect, 1955 C.Herring pointed out: this piezo resistance effect is due to stress the role of the lead conductor and Valence electron variation with energy status, and number of carriers and the migration rate of change of a phenomenon.

Japan, 1970 began research and development, the first application in sphygmomanometer, then in the process control field and car engine control components for a wide range of applications. In recent years in household appliances, Assembly robot applications commonly used electronic pressure sensors for pressure control, pressure control and determine the vacuum absorption effect.

Figure 1

Working principle

Figure 1 to PS pressure sensor section chart, diagram 2 for its sensor parts of the structure.

As shown, the pressure sensor wafer with a layer of diffusion resistance of the body, if the resistance in the pressure as piezoelectric resistance effect, its resistance value changes. Be part of the strain that the diaphragm as easy to sense pressure and thinning, in order to alleviate the stress from the sensor, the cradle will pressure sensor chip is installed in the glass base.

Figure 2

Figure 2 (b) below, when the cavity section plus a certain amount of pressure, the diaphragm is a degree of stretching or shrinking the resulting deformation.

Piezo resistive arrangement method as shown in Figure 3, subject to tensile resistance R2 and increase of the resistance of the R4; subject to compression resistance reduces the resistance of the R1 and R3.

Figure 3

Because of the piezo resistance as in Figure 4, if the bridge structure comprising connecting them to the constant current source, due to the decrease of pressure will be output to the output voltage, Δ Δ V V's size from next-decision:

-In (1), when the pressure to zero of Δ V equal to the offset voltage Voffset, ideally we want Voffset = 0V, actually generate diffusion resistance of the body, due to the formation of diffusion resistance body size of different and there are small differences in the concentration of impurities and, therefore, always have a voltage values exist.

Pressure to zero, R1 = R3 = R2 = R4 = R, we put together with a certain amount of pressure is R1, R2 resistors changes some credited to Δ R; the R3, R4 resistance changes some credited-Δ R, then (1)-simplified to:

ΔV=ΔRI (2)

The Δ V relative pressure rendered almost entirely linear features, just as the temperature changes.

Peripheral circuit design

Figure 4 is a PS pressure sensor of the external circuit design examples, diagrams with constant current source to drive the pressure sensor.

Figure 4

Because the bridge when the output voltage unbalance of relatively small, so you must use the amplifier IC1b and IC1C to zoom in.

Figure adjusted for bias VR1 and VR2-pressure sensitivity adjustment, when no pressure VR3 output voltage adjustment, C1, C2 is used to remove noise. In addition, if the power voltage fluctuations, will cause the output voltage change, so must give circuits provide a stable power supply.

Application examples

Figure 6 is a PS pressure sensor for automatic washing machine in the application instance.

As shown, the use of gas chambers, the water level in the different circumstances changes of water pressure, as the air pressure changes detected, which can be set to automatically stop the water washing.

Figure 5