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Motorola Sensor Device Data
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When designing a system based on the MPX2010, it is
important to take into account errors due to parametric varia-
tion of the sensor (i.e. offset calibration, span calibration, TcS,
TcO), power supply and the inherent errors of the amplification
circuit. The offset and span errors greatly determines the reso-
lution of the system (which adds to the system error). Even
though the system offset error can be nulled out by auto–zero-
ing, these errors must be accounted for when setting the sys-
tem gain (see AN1556 for more details). This forces the total
span of the system to be smaller, because we must reserve an
extra headroom from the total span to account for amplifier
and A/D variations (i.e. amp. sat. voltage, power supply varia-
tion, A/D quantization error, and gain errors ). If these errors
are not accounted for, it could, for example, result in non–
linearity errors if the sensor span or offset error causes the
amplified output of the sensor to reach the saturation voltage
of the amplifier.
As an example, a MPX2010 sensor system is designed
which has a range of 600 mmH2O FS range with a +/– 5 % FS
RMS error. The system uses a +5 V +/– 5% linear regulated
power supply, a MC33272 dual op–amp and a 1% resistors.
Table 3 shows the resulting specification and component
values for the system based on MPX2010 sensor.
Table 3. MPX2010 Sensor System Values
MPX2010 Sensor Design
Parameter
Description
Reg Power Supply
Value
5
Units
V
Vcc
Differential Gain
Gain
433
V/V
Vout_FS
Full Scale Span
3.02
V
Vref
Offset Reference
0.66
V
Parts List
U1A,U1B
MC33272 Op–amp
R1
Gain Resistor
39.2K
Ohms
R2
Gain Resistor
90.9
Ohms
R3
Gain Resistor
909
Ohms
R4
Gain Resistor
392K
Ohms
R + S1
Level Shift Resistor
1K
Ohms
R + S2
Level Shift Resistor
150
Ohms
X1
MPX2010
Table 4. Performance Comparison between MPX2010 and MPXV4006G Solution
MPX2010 Solution Error
(FS = 600 mmH2O)
+/– % FS
7.19
MPXV4006G Solution Error
(FS = 612 mmH2O)
+/– % FS
3.00
Error Contribution
+/– mmH2O
43
+/– mmH2O
18
Max Sensor Error
System Resolution (A/D + Amplification)
1.30
8
0.80
5
System Error (Sensor + A/D + Amplification)
7.3
44
3.10
19
System Error with Auto–Zero
4.6
28
3
19
Note that the error due to system resolution is higher for the
MPX2010 solution (+/– 2 bit A/D accuracy). This is because
the MPX2010 span is limited as discussed above. Also, this
accuracy assumes that the amplifier does not induce signifi-
cant errors. As noted MPXV4006G sensor has better overall
accuracy. The system resolution is very good because of its
large span (4.6 V versus 3.0 V typical).
F
Freescale Semiconductor, Inc.
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