MAX1457 Datasheet, PDF (10/12 Pages) Maxim Integrated Products – 0.1%-Accurate Signal Conditioner for Piezoresistive Sensor Compensation

0.1%-Accurate Signal Conditioner
for Piezoresistive Sensor Compensation
DIGITAL
ECS[1:N], MCS[1:N]
MULTIPLEXER
ECS1
MODULE 1
MCS1
MCS
ECS2
MODULE 2
•••
MCS2
MCS
ECS N
MODULE N
MCS N
MCS
+5V
VOUT
DVM
ECLK
EDI
EDO
ECS
EDO
V_DD
ECLK
EDI
V_OUT
V_SS
ECS
ECS
EDO
V_DD
ECLK
EDI
V_OUT
V_SS
EDO
V_DD
•••
•••
ECLK
EDI
V_OUT
V_SS
•••
•••
•••
•••
TEST
OVEN
Figure 7. Automated Test System Concept
7) Perform curve-fitting to test data.
8) Based on a curve-fit algorithm, calculate up to 120
sets of offset and FSO correcting values.
9) Download correction coefficients to transducer
EEPROM.
10) Perform a final test.
The resulting transducer temperature errors are limited by
the following factors:
• Number of selected segments for compensation (up to
120).
• Accuracy of the curve fitting, which depends on the
algorithm used, the number of test temperatures, and
the sensor temperature error’s shape.
• Repeatability of the sensor performance. This will limit
the MAX1457’s accuracy.
Sensor Calibration and
Compensation Example
Calibration and compensation requirements for a sen-
sor involve conversion of the sensor-specific perfor-
mance into a normalized output curve. An example of
the MAX1457’s capabilities is shown in Table 1.
As shown in Table 1, a repeatable piezoresistive sensor
with an initial offset of 16.4mV and FSO of 55.8mV was
converted into a compensated transducer (utilizing the
piezoresistive sensor with the MAX1457) with an offset
of 0.500V and a span of 4.000V. Nonlinear sensor offset
and FSO temperature errors, which were on the order
of 4% to 5% FSO, were reduced to under ±0.1% FSO.
The graphs in Figure 8 show the output of the uncom-
pensated sensor and the output of the compensated
transducer.
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