3–388
Motorola Sensor Device Data
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Table 1. Actual versus Modeled R(Temp)
Temp
Measured
R(Temp)
406
Compound
Model
406
Linear
Model
372
40
25
418
418
395
0
445
445
434
25
474
474
474
50
509
508
513
75
545
545
552
100
585
584
592
125
627
626
632
150
671
671
671
In Table 1, 25 and 150 degree Celsius data points were used
to determine both linear and compound temperature coeffi-
cients. Therefore, measured values, linear model values and
compound model values all match at these two temperatures.
At other temperatures, the linear model exhibits errors that are
significant when modeling piezoresistive pressure sensors.
The compound model, however, tracks with measured values
to within 1 Ohm out of 500 Ohms.
EXAMPLES
Two examples of what the model outputs look like are
shown in Figures 4 and 5. Figure 4 shows a sweep of pressure
versus output voltage (VOUT) at 0, 25, and 85 degrees Celsius,
for an MPX2010 sensor. It has the expected 0 to 25 mV output
voltage, given a 0 to 10 kPa pressure input. At these three
temperatures, compensation is sufficiently good that all three
plots look like the same straight line.
Figure 4. MPX2010 VOUT versus Pressure and Temperature
To produce the plot in Figure 4, the stimulus section is set
up as follows, and V(2,4) is probed.
***************************STIMULUS****************************
VCC 6 0 DC=10;
DC BIAS FROM PIN 3 TO PIN 1
.PARAM PRESSURE=0;
INPUT PRESSURE (kPa)
.DC PARAM PRESSURE 0_Kpa 10_Kpa .5_Kpa TEMP
LIST 0 25 85
*.DC PARAM TEMP –40 125 5
*
This is the default configuration with which the model is
shipped. To change to a sweep of zero pressure voltage ver-
sus temperature, an asterisk is placed on line 3 and removed
from line 4. The stimulus section then looks as follows:
****************************STIMULUS***************************
VCC 6 0 DC=10;
DC BIAS FROM PIN 3 TO PIN 1
.PARAM PRESSURE=0;
INPUT PRESSURE (kPa)
*.DC PARAM PRESSURE 0_Kpa 10_Kpa .5_Kpa TEMP
LIST 0 25 85
.DC PARAM TEMP –40 125 5
*
Again, V(2,4) is probed. The resulting output appears in
Figure 5.
This plot shows offset versus temperature performance that
is typical of MPX2000 series sensors. From
degrees Celsius, offset compensation is quite good. Above 85
degrees there is a hook in this curve, that is an important attrib-
ute of the sensor’s performance.
40 to
85
F
Freescale Semiconductor, Inc.
n
.