Datasheet
8
Signal Chain Design Guide
Weight and pressure measurement have been among
the most popular applications for medical, industrial,
automotive and consumer industries. In recent years,
the MEMS pressure/accelerometer devices have
become widely used in many applications and support
our modern life style. The majority of weight scale and
pressure measurement circuits use bridge type ratiometric
configuration. In this case, the output voltage range
from the sensor circuit is proportional to the excitation
voltage. The following circuit shows an example weight
measurement application. In the figure, the output from
the load cell is amplified by the low noise op amplifier and
fed to the MCP3421 18-bit delta sigma ADC.
Example of Weight Measurement Circuit
Configuration (MCP3421DM-WS)
MCP3421
PIC
®
MCU
–
+
–
+
ADC
½ MCP6V02
½ MCP6V02
V
E
xcitation
Load Cell
Sensor Signal Conditioning
Weight and Pressure Sensing Applications
The following circuit shows an example of pressure
measurement using the MCP3551 22-bit Delta-Sigma
ADC. In this example, the MCP3551 is directly connected
to the NPP-301 sensor output without using the sensor
signal conditioning circuit. Since the MCP3551 uses an
external reference input, the same supply voltage is used
for the ADC reference and Vdd, and the sensor excitation.
Therefore, the variation in the sensor excitation source is
naturally cancelled out.
Example of Pressure Measurement Circuit
Configuration using the MCP3551 Device
R
2
SPI
V
REF
SCK
SDO
CS
MCP3551
5, 6, 7
1
2
3
4
8
V
SS
V
IN+
V
IN-
To V
DD
V
DD
0.1 µF 1.0 µF
NPP-301
R
1
R
4
R
3
MCU
∆V ~ [(∆R
2
+ ∆R
4
) - (∆R
1
+∆R
3
)]/4R * V
DD
With R
1
= R
2
= R
3
= R
4
= R
0.00
PSI