OP113_07 Datasheet, PDF (14/24 Pages) Analog Devices – Low Noise, Low Drift Single-Supply Operational Amplifiers

OP113/OP213/OP413
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.
+15V
R5
1kΩ
8 ₊₃
+10V
1
2N2219A
1
A2
3
–2
1/2
OP213
9
2
16
AD588BQ
–15V
14
15
8
10
350Ω
LOAD
CELL
+10V
100mV
F.S.
4 6 11 12 13 7
R3
17.2kΩ R4
0.1% 500Ω
6–
+ _10µF
CMRR TRIM
10-TURN
T.C. LESS THAN 50ppm/°C
A1
7
5 + _{4 1/2}
OP213
OUTPUT
0 10V
FS
–15V
R1
R2
17.2kΩ 301Ω
0.1% 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.
350Ω
35mV
FS
5V
2N2222A
8
1/2 ^{+ 3}
1 _OP295
4 ^–2
2.5V
2
IN
6 OUT REF43
GND
4
4V
R8
12kΩ
R7
20kΩ
3+
1/2
OP213
2–
1
R2
20kΩ
R3
20kΩ
5V
8
5 + _1/2
OP295 ⁷
6–
4
OUTPUT
0V 3.5V
R4
100kΩ
R1
100kΩ
R5
R6
2.1kΩ 27.4Ω
R_G = 2127.4Ω
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.
Rev. F | Page 14 of 24