OP113_15 Datasheet, PDF (15/24 Pages) Analog Devices – Low Noise, Low Drift Single-Supply Operational Amplifiers

–15V +15V
16
2
11
14
12
13 AD588BQ ¹⁵
4
1
6
3
7 9 8 10
+
10µF
R3
50Ω
R1
8.25kΩ
R_G FULL SCALE ADJUST
R2
8.25kΩ
R5 R7
4.02kΩ 100Ω
+15V
100Ω
RTD
R_W1
R_W2
R4
100Ω
6– ⁸
A2
7
5 + _{4 1/2}
OP213
V_OUT (10mV/°C)
–1.5V = –150°C
+5V = +500°C
R_W3
2–
–15V
R8
49.9kΩ
R9
5kΩ
LINEARITY
ADJUST
@1/2 FS
A1
1
3+
1/2
OP213
Figure 43. Ultraprecision RTD Amplifier
To calibrate the circuit, first immerse the RTD in a 0°C ice bath
or substitute an exact 100 Ω resistor in place of the RTD. Adjust
the zero adjust potentiometer for a 0 V output, and then set R9,
linearity adjust potentiometer, to the middle of its adjustment
range. Substitute a 280.9 Ω resistor (equivalent to 500°C) in
place of the RTD, and adjust the full-scale adjust potentiometer
for a full-scale voltage of 5 V.
To calibrate out the nonlinearity, substitute a 194.07 Ω resistor
(equivalent to 250°C) in place of the RTD, and then adjust the
linearity adjust potentiometer for a 2.5 V output. Check and
readjust the full-scale and half-scale as needed.
Once calibrated, the amplifier outputs a 10 mV/°C temperature
coefficient with an accuracy better than ±0.5°C over an RTD
measurement range of −150°C to +500°C. Indeed the amplifier
can be calibrated to a higher temperature range, up to 850°C.
A HIGH ACCURACY THERMOCOUPLE AMPLIFIER
Figure 44 shows a popular K-type thermocouple amplifier with
cold-junction compensation. Operating from a single 12 V
supply, the OPx13 family’s low noise allows temperature
measurement to better than 0.02°C resolution over a 0°C to
1000°C range. The cold-junction error is corrected by using an
inexpensive silicon diode as a temperature measuring device.
It should be placed as close to the two terminating junctions as
physically possible. An aluminum block might serve well as an
isothermal system.
OP113/OP213/OP413
12V
2 REF02EZ 6
+
0.1µF
4
1N4148
D1
K-TYPE
THERMOCOUPLE
40.7µV/°C
––
++
R4
5.62kΩ
5V
R1
10.7kΩ
R5
40.2kΩ
R9
124kΩ
12V
10µF
+
R2
R8
2.74kΩ 453Ω
R6
200Ω
R3
53.6Ω
0.1µF
+
2– ⁸
1/2
OP213
3+ ₄
1
0V TO 10V
(0°C TO 1000°C)
Figure 44. Accurate K-Type Thermocouple Amplifier
R6 should be adjusted for a 0 V output with the thermocouple
measuring tip immersed in a 0°C ice bath. When calibrating, be
sure to adjust R6 initially to cause the output to swing in the
positive direction first. Then back off in the negative direction
until the output just stops changing.
AN ULTRALOW NOISE, SINGLE SUPPLY
INSTRUMENTATION AMPLIFIER
Extremely low noise instrumentation amplifiers can be built
using the OPx13 family. Such an amplifier that operates from a
single supply is shown in Figure 45. Resistors R1 to R5 should
be of high precision and low drift type to maximize CMRR
performance. Although the two inputs are capable of operating
to 0 V, the gain of −100 configuration limits the amplifier input
common-mode voltage to 0.33 V.
5V TO 36V
+
V_IN
–
*R1
10kΩ
+
1/2
OP213
– _*R2
10kΩ
*R3
10kΩ
+
1/2
OP213
–
*R4
10kΩ
V_OUT
*R_G
(200Ω + 12.7Ω)
GAIN
=
20kΩ
R_G
+
6
*ALL RESISTORS ±0.1%, ±25ppm/°C.
Figure 45. Ultralow Noise, Single Supply Instrumentation Amplifier
SUPPLY SPLITTER CIRCUIT
The OPx13 family has excellent frequency response
characteristics that make it an ideal pseudoground reference
generator, as shown in Figure 46. The OPx13 family serves as a
voltage follower buffer. In addition, it drives a large capacitor
that serves as a charge reservoir to minimize transient load
changes, as well as a low impedance output device at high
frequencies. The circuit easily supplies 25 mA load current with
good settling characteristics.
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