MPXM2102AS datasheet(561/670 Pages) MOTOROLA

561 / 670 page

AN4007

3–415

Motorola Sensor Device Data

www.motorola.com/semiconductors

Motorola’s New MPXV6115VC6U

Vacuum Sensor

PIEZORESISTIVE/AMPLIFIED SENSORS

Motorola’s pressure sensors are based on a piezoresistive

technology that consists of a silicon micromachined

diaphragm and a diffused piezoresistive strain gauge. When

vacuum or pressure is applied on the die, the diaphragm is

deformed and stressed. The resulting constraints create a

variation of resistance in the piezoresistive strain gauge. In

order to read this variation, an excitation current passes

through the gauge, and a voltage proportional to the applied

pressure and excitation current appears between the voltage

taps. To get an accurate pressure reading, such a sensing

element needs usually to be calibrated, temperature

compensated and amplified.

In order to solve the inherent limitation of the basic sensing

element, Motorola produces an entire family of calibrated,

thermally compensated and amplified pressure sensors

(Figure 4) called Integrated Pressure Sensors (IPS).

The IPS is a state of the art, monolithic, amplified and

signal–conditioned silicon pressure sensor.

The sensor

combines advanced micromachining techniques, thin film

memorization and bipolar semiconductor processing

provide an accurate, high–level analog output that is

proportional to the applied pressure. IPS sensors can be

directly connected to an A/D converter.

Figure 4. Integrated Pressure Sensor Block Diagram

SENSING

ELEMENT

THERMAL

COMPENSATION

AMPLIFIER

PRESSURE MEASUREMENT CONVENTION

Pressure measurements can be divided into three different

categories: absolute, gage and differential pressure.

Absolute pressure refers to the absolute value of the force

per unit area exerted on a surface by a fluid. Therefore, the

absolute pressure is the difference between the pressure at a

given point in a fluid and the absolute zero of pressure or a

perfect vacuum.

Gage pressure is the measurement of the difference

between the absolute pressure and the local atmospheric

pressure. Local atmospheric pressure can vary depending on

ambient temperature, altitude and local weather conditions.

The standard atmospheric pressure at sea level and 20

_C is

101.325 kPa absolute.

When referring to pressure

measurement, it is critical to specify what reference the

pressure is related to: gage or absolute. A gage pressure by

convention is always positive. A ‘negative’ gage pressure is

defined as vacuum. Figure 5 shows the relationship between

absolute, gage pressure and vacuum.

Differential pressure is simply the measurement of one

unknown pressure with reference to another unknown

pressure. The pressure measured is the difference between

the two unknown pressures. Since a differential pressure is

a measure of one pressure referenced to another, it is not

necessary to specify a pressure reference.

Figure 5. Pressure Convention

ABSOLUTE

GAGE (+)

LOCAL ATMOSPHERIC PRESSURE

VACUUM (–)

ATMOSPHERIC

ABSOLUTE

Freescale Semiconductor, Inc.

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Go to: www.freescale.com

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