3
Motorola Sensor Device Data
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 2) 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 pres-
sure.
Figure 2. Linearity Specification Comparison
LEAST
SQUARE
DEVIATION
R
PRESSURE (% FULLSCALE)
0
50
100
END POINT
STRAIGHT LINE FIT
EXAGGERATED
PERFORMANCE
CURVE
LEAST SQUARES FIT
STRAIGHT LINE
DEVIATION
OFFSET
ON–CHIP TEMPERATURE COMPENSATION and CALIBRATION
Figure 3 shows the output characteristics of the MPX7100
series at 25
°
C. The output is directly proportional to the dif-
ferential pressure and is essentially a straight line.
The effects of temperature on Full Scale Span and Offset
are very small and are shown under Operating Characteris-
tics.
Figure 3. Output versus Pressure Differential
Figure 4. Cross–Sectional Diagrams (Not to Scale)
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DIFFERENTIAL/GAUGE ELEMENT
P2
SILICONE GEL
DIE COAT
WIRE BOND
LEAD FRAME
DIFFERENTIAL/GAUGE
DIE
STAINLESS STEEL
METAL COVER
EPOXY
CASE
DIE
BOND
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ABSOLUTE ELEMENT
P2
SILICONE GEL
DIE COAT
WIRE BOND
LEAD FRAME
ABSOLUTE
DIE
STAINLESS STEEL
METAL COVER
EPOXY
CASE
DIE
BOND
O
kPa
PSI
40
35
30
25
20
15
10
5
0
–50
25
3.62
50
7.25
75
10.87
100
14.5
SPAN
RANGE
(TYP)
OFFSET
(TYP)
VS = 10 Vdc
TA = 25
°
C
P1 > P2
MAX
TYP
MIN
Figure 4 illustrates the absolute sensing configuration (right)
and the differential or gauge configuration in the basic chip
carrier (Case 344–15). A silicone gel isolates the die surface
and wire bonds from the environment, while allowing the pres-
sure signal to be transmitted to the silicon diaphragm.
The MPX7100 series pressure sensor operating charac-
teristics and internal reliability and qualification tests are
based on use of dry air as the pressure media. Media other
than dry air may have adverse effects on sensor perfor-
mance and long term reliability. Contact the factory for in-
formation regarding media compatibility in your application.