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Motorola Sensor Device Data
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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 to
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
P
THERMAL
COMPENSATION
AMPLIFIER
V
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
F
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