OP113FS datasheet(14/24 Pages) AD

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OP113/OP213/OP413

Rev. F | Page 14 of 24

APPLICATION CIRCUITS

A HIGH PRECISION INDUSTRIAL LOAD-CELL

SCALE AMPLIFIER

The OPx13 family makes an excellent amplifier for

conditioning a load-cell bridge. Its low noise greatly improves

the signal resolution, allowing the load cell to operate with a

smaller output range, thus reducing its nonlinearity. Figure 41

shows one half of the OPx13 family used to generate a very

stable 10 V bridge excitation voltage while the second amplifier

provides a differential gain. R4 should be trimmed for

maximum common-mode rejection.

11 12

AD588BQ

2N2219A

+10V

+15V

–15V

+10V

OUTPUT

010V

–15V

1/2

OP213

–

+ 10µF

–

CMRR TRIM

10-TURN

T.C. LESS THAN 50ppm/°C

350Ω

LOAD

CELL

100mV

F.S.

1kΩ

1/2

OP213

17.2kΩ

0.1%

301Ω

0.1%

500Ω

17.2kΩ

0.1%

Figure 41. Precision Load-Cell Scale Amplifier

A LOW VOLTAGE, SINGLE SUPPLY STRAIN GAGE

AMPLIFIER

The true zero swing capability of the OPx13 family allows the

amplifier in Figure 42 to amplify the strain gage bridge

accurately even with no signal input while being powered by a

single 5 V supply. A stable 4 V bridge voltage is made possible

by the rail-to-rail OP295 amplifier, whose output can swing to

within a millivolt of either rail. This high voltage swing greatly

increases the bridge output signal without a corresponding

increase in bridge input.

2N2222A

2.5V

1/2

OP295

OUT

GND

REF43

1/2

OP213

100kΩ

20kΩ

27.4Ω

2.1kΩ

20kΩ

100kΩ

1/2

OP295

RG = 2127.4Ω

OUTPUT

3.5V

–

350Ω

35mV

12kΩ

20kΩ

–

Figure 42. Single Supply Strain Gage Amplifier

A HIGH ACCURACY LINEARIZED RTD

THERMOMETER AMPLIFIER

Zero suppressing the bridge facilitates simple linearization of

the resistor temperature device (RTD) by feeding back a small

amount of the output signal to the RTD. In Figure 43, the left

leg of the bridge is servoed to a virtual ground voltage by

Amplifier A1, and the right leg of the bridge is servoed to 0 V

by Amplifier A2. This eliminates any error resulting from

common-mode voltage change in the amplifier. A 3-wire RTD

is used to balance the wire resistance on both legs of the bridge,

thereby reducing temperature mismatch errors. The 5 V bridge

excitation is derived from the extremely stable AD588 reference

device with 1.5 ppm/°C drift performance.

Linearization of the RTD is done by feeding a fraction of the

output voltage back to the RTD in the form of a current. With

just the right amount of positive feedback, the amplifier output

will be linearly proportional to the temperature of the RTD.

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