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 or (2) a least
squares best line fit (see Figure 3). 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 MPX2700
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.
50
V
= 10 V
= 25°C
S
40
T
A
TYP
P1 > P2
SILICONE
STAINLESS STEEL
METAL COVER
DIE
DIE COAT
30
20
10
MAX
P1
P2
SPAN
RANGE
(TYP)
WIRE BOND
MIN
RTV DIE
BOND
LEAD
FRAME
0
PSI
kPa
20
140
40
280
60
420
80
560
100
700
–5
OFFSET
EPOXY CASE
Figure 3. Output versus Pressure Differential
Figure 4. Cross–Section of Differential Pressure
Sensor Die in Its Basic Package (Not to Scale)
Figure 4 shows the cross section of the Motorola MPX
pressure sensor die in the chip carrier package. 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. MPX2700 series
pressure sensor operating characteristics and internal reli-
ability 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 performance and long term
reliability. Contact the factory for information regarding media
compatibility in your application.
Motorola Sensor Device Data
3