MPXM2102AS datasheet(155/670 Pages) MOTOROLA

155 / 670 page

Figure 4. Linearity Specification Comparison

LEAST SQUARE

DEVIATION

100

PRESSURE (% FULLSCALE)

STRAIGHT

LINE

DEVIATION

LEAST SQUARES FIT

EXAGGERATED

PERFORMANCE

CURVE

OFFSET

END POINT

STRAIGHT LINE FIT

3–9

Motorola Sensor Device Data

www.motorola.com/semiconductors

LINEARITY

Linearity refers to how well a transducer’s output follows

the equation: Vout = Voff + sensitivity x P over the operating

pressure range. There are two basic methods for calculating

nonlinearity: (1) end point straight line fit (see Figure 4) or

(2) a least squares best line fit. While a least squares fit gives

the “best case” linearity error (lower numerical value), the

calculations required are burdensome.

Conversely, an end point fit will give the “worst case” error

(often more desirable in error budget calculations) and the

calculations are more straightforward for the user. Motorola’s

specified pressure sensor linearities are based on the end

point straight line method measured at the midrange pressure.

OPERATION

Motorola pressure sensors provide three types

of pressure measurement: Absolute Pressure,

Differential Pressure and Gauge Pressure.

Absolute Pressure Sensors measure an

external pressure relative to a zero–pressure

reference (vacuum) sealed inside the reference

chamber of the die during manufacture. This

corresponds to a deflection of the diaphragm

equal to approximately 14.5 psi (one atmo-

sphere), generating a quiescent full–scale output

for the MPXH6101A6T1 (14.5 psi) sensor, and a

half–scale output for the MPX4200A (29 psi)

device. Measurement of external pressure is

accomplished by applying a relative negative

pressure to the “Pressure” side of the sensor.

Differential Pressure Sensors measure the

difference between pressures applied simulta-

neously to opposite sides of the diaphragm. A

positive pressure applied to the “Pressure” side

generates the same (positive) output as an equal

negative pressure applied to the “Vacuum” side.

Figure 5. Pressure Measurements

Gauge Pressure readings are a special case of differential measure-

ments in which the pressure applied to the “Pressure” side is measured

against the ambient atmospheric pressure applied to the “Vacuum” side

through the vent hole in the chip of the differential pressure sensor

elements.

NEGATIVE PRESSURE

VOFF

1 ATM PMAX

INCREASING VACUUM

INCREASING PRESSURE

POSITIVE PRESSURE

NEGATIVE

PRESSURE

VOFF

DIFFERENTIAL PRESSURE

INCREASING

PMAX

Absolute

Sensor

Differential

Sensor

VACUUM

Motorola sensing elements can withstand pressure inputs as high as four times their rated

capacity, although accuracy at pressures exceeding the rated pressure will be reduced.

When excessive pressure is reduced, the previous linearity is immediately restored.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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