Pressure
Temperature Compensation
Figure 2
shows the typical output characteristics of the
MPX53 series over temperature.
The piezoresistive pressure sensor element is a
semiconductor device which gives an electrical output signal
proportional to the pressure applied to the device. This device
uses a unique transverse voltage diffused semiconductor
strain gauge which is sensitive to stresses produced in a thin
silicon diaphragm by the applied pressure.
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 MPX2053 series sensors.
Several approaches to external temperature
compensation over –40 to +125°C and 0 to +80°C are
presented in Freescale Application 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 (see
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.
illustrates the differential or gauge configuration in
the unibody chip carrier (Case 344). 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 MPX53 series pressure sensor operating
characteristics 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
performance and long term reliability. Refer to application
note AN3728, for more information regarding media
compatibility.
+25°C
–40°C
Span
Range
(Typ)
100
90
80
70
Output (mVdc)
60
50
40
MPX53
V
S
= 3 Vdc
P1 > P2
30
20
10
0
PSI 0
kPa 0
+125ºC
Offset
(Typ)
1
10
2
3
4
5
6
20
30
40
Pressure Differential
7
50
8
Figure 2. Output vs. Pressure Differential
90
80
70
60
50
Output (mVdc)
40
30
20
10
0
0
Pressure (kPA)
Offset
(V
OFF
)
MAX
P
OP
Theoretical
Lead Frame
P2
RTV Die
Bond
Actual
Span
(V
FSS
)
Wire Bond
Linearity
Stainless Steel
Metal Cover
P1
Epoxy
Case
Silicone
Die Coat
Die
Figure 3. Linearity Specification Comparison
Figure 4. Unibody Package — Cross-Sectional Diagram
(Not to Scale)
MPX53
4
Sensors
Freescale Semiconductor
FREESCALE [ FREESCALE SEMICONDUCTOR, INC ]
