LINEARITY
Linearity refers to how well a transducer’s output follows
LEAST SQUARES FIT
EXAGGERATED
PERFORMANCE
CURVE
the equation: V
= V + sensitivity x P over the operating
out
off
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.
STRAIGHT LINE
DEVIATION
LEAST
SQUARE
DEVIATION
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.
END POINT
STRAIGHT LINE FIT
OFFSET
50
PRESSURE (% FULLSCALE)
100
0
Figure 2. Linearity Specification Comparison
ON–CHIP TEMPERATURE COMPENSATION and CALIBRATION
Figure 3 shows the output characteristics of the MPX2100
series at 25°C. The output is directly proportional to the
differential 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.
40
V
T
= 10 Vdc
= 25°C
S
A
35
30
25
20
15
10
5
P1 > P2
TYP
SPAN
RANGE
(TYP)
MAX
MIN
0
OFFSET
(TYP)
–5
0
25
3.62
50
7.25
75
10.87
100
14.5
kPa
PSI
Figure 3. Output versus Pressure Differential
SILICONE GEL DIFFERENTIAL/GAUGE
DIE COAT DIE
SILICONE GEL
DIE COAT
ABSOLUTE
DIE
STAINLESS STEEL
METAL COVER
STAINLESS STEEL
METAL COVER
P1
P1
EPOXY
CASE
EPOXY
CASE
WIRE BOND
WIRE BOND
DIE
BOND
LEAD FRAME
LEAD FRAME
DIE
BOND
DIFFERENTIAL/GAUGE ELEMENT
P2
ABSOLUTE ELEMENT
P2
Figure 4. Cross–Sectional Diagrams (Not to Scale)
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 pressure signal to be transmitted to the silicon
diaphragm.
The MPX2100 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.
Motorola Sensor Device Data
3