ADC121S021

IN

V

+

LM4140A

6

2

1,4,7,8

3

V

+

1 PF

+

-

0.1 PF

10 PF

V

+

+

-

+

-

-

+

12 k:

10 k:

40 k:

½

LMP2232

R+'R

R+'R

R

R

V

+

V

+

V

+

12 k:

10 k:

40 k:

1 k:

LMP2231

½

LMP2232

LMP2231

GND

EXCITATION

SOURCE

(a)

1 +

¨

¨

©

§

1 +

¨

¨

©

§

-

=

EXCITATION

SOURCE

R + 'R

R - 'R

R - 'R

R + 'R

(b)

'R

R

LMP2231

www.ti.com

SNOSB01E – JANUARY 2008 – REVISED MARCH 2013

Figure 51 (a) shows a typical bridge sensor and Figure 51(b) shows the bridge with four sensors. R in

Figure 51(b) is the nominal value of the sense resistor and the deviations from R are proportional to the quantity

being measured.

Figure 51. Bridge Sensor

Instrumentation amplifiers are great for interfacing with bridge sensors. Bridge sensors often sense a very small

differential signal in the presence of a larger common mode voltage. Instrumentation amplifiers reject this

common mode signal.

Figure 52 shows a strain gauge bridge amplifier. In this application the LMP2231 is used to buffer the LM4140's

precision output voltage. The LM4140A is a precision voltage reference. The other three LMP2231s are used to

amplified signal is then fed into the ADC121S021 which is a 12-bit analog to digital converter. This circuit works

on a single supply voltage of 5V.

Figure 52. Strain Gauge Bridge Amplifier

Copyright © 2008–2013, Texas Instruments Incorporated

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