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Motorola Sensor Device Data
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TCR — Temperature coefficient of bridge resistance;
shaped by a Table that accounts for cold temperature
non–linearity’s
TCR2 — Temperature coefficient of contact resistance;
shaped by a Table that accounts for cold temperature
non–linearity’s
TCS — Temperature coefficient of Span; shaped by a Table
that accounts for cold temperature non–linearity’s
RPH — Bridge Resistance (RS1 and RS3) modified by
pressure and temperature
ROH — Offset Component of Bridge Resistors RS1 and RS3
RPL — Bridge Resistance (RS2 and RS4) modified by
pressure and temperature
ROL — Offset Component of Bridge Resistors RS2 and RS4
KB — Bias Constant; adjusts KP for bias voltage effects of
span compensation network (MPX2000 and MPX5000
series sensors)
KBT — Bias Constant; adjusts KO for bias voltage effects of
span compensation network (MPX2000 and MPX5000
series sensors)
GAIN — Instrumentation amplifier gain; differential gain
(MPX5000 series)
ROFF — Offset resistance; determines value of RS13
(MPX5000 series)
After these calculations are made, the final bridge resis-
tance calculation is performed in the circuit section. The value
for bridge resistors RS1 and RS3 is RPH + ROH. Bridge resis-
tors RS2 and RS4 are equal to RPL–ROL.
CIRCUIT
Three circuits are used to model the three sensor families,
one each for the Uncompensated series, MPX2000 series,
and MPX5000 series sensors. Schematics that are derived
from the circuit netlists are shown in Figures 1, 2, and 3. They
are discussed beginning with the Uncompensated series,
which is the least complex.
Uncompensated Series:
The Uncompensated Series sensors (MPX10, MPX50, and
MPX100) are modeled as Wheatstone bridges. In the configu-
ration that is shown in Figure 1, resistors RS2 and RS4
decrease in value as pressure is applied. Similarly, RS1 and
RS3 increase in value as pressure is applied. Resistors RS5
and RS7 are contact resistors. They represent real physical
resistors that are used to make contact to the bridge. Resistors
RS6 and RS8 are included to satisfy PSPICE’s requirement
for no floating nodes. That’s it. The netlist in this model is quite
simple. The hard part is calculating the values for RS1, RS2,
RS3, and RS4.
Figure 1. MPX10 and 100 PSPICE Compound Coefficient Model
3
0
2
4
5
1
**
**
**
**
*
*
NOTES:
*TEMPERATURE SENSITIVE
**TEMPERATURE & PRESSURE SENSITIVE
RS4
475
RS1
475
RS2
475
RS3
475
RS8
1000MEG
RS7
675
RS5
750
RS6
1000MEG
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Freescale Semiconductor, Inc.
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