MPX12
Sensors
Freescale Semiconductor 5
Pressure
Temperature Compensation
Figure 2 shows the typical output characteristics of the
MPX12 series over temperature.
Because this strain gauge is an integral part of the silicon
diaphragm, there are no temperature effects due to
differences in the thermal expansion of the strain gauge and
the diaphragm, as are often encountered in bonded strain
gauge pressure sensors. However, the properties of the
strain gauge itself are temperature dependent, requiring that
the device be temperature compensated if it is to be used
over an extensive temperature range.
Temperature compensation and offset calibration can be
achieved rather simply with additional resistive components, or
by designing your system using the MPX2010D series sensor.
Several approaches to external temperature
compensation over both –40 to +125°C and 0 to +80°C
ranges are presented in Applications Note AN840.
LINEARITY
Linearity refers to how well a transducer's output follows
the equation: V
OUT
= V
OFF
+ sensitivity x P over the operating
pressure range (Figure 3). There are two basic methods for
calculating nonlinearity: (1) end point straight line fit 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.
Freescale’s specified pressure sensor linearities are based
on the end point straight line method measured at the
midrange pressure.
Figure 2. Output vs. Pressure Differential
Figure 3. Linearity Specification Comparison
Pressure Differential
Output (mVdc)
80
70
60
50
40
30
20
10
0
0
0.3
2.0
0.6
4.0
0.9
6.0
1.2
8.0 10
1.5
PSI
kPa
Span
Range
(Typ)
Offset
(Typ)
V
S
= 3 V
DC
P1 > P2
-40°C
+25°C
+125°C
Linearity
Actual
Theoretical
Offset
(V
OFF
)
Max
P
OP
Output (mVdc)
Pressure (kPa)
70
60
50
40
30
20
10
0
0
Span
(V
FSS
)
80
