OP113/OP213/OP413
Rev. F | Page 15 of 24
6
5
4
7
A2
R5
4.02k
R7
100
8
+15V
–15V
1/2
OP213
R2
8.25k
R1
8.25k
R3
50
A1
3
2
1
6
4
13
11
12
7
9
8
10
16
2
14
15
1
3
+15V
–15V
AD588BQ
1/2
OP213
+
–
+
–
RG FULL SCALE ADJUST
+
RW1
RW2
RW3
VOUT (10mV/°C)
–1.5V = –150°C
+5V = +500°C
R9
5k
LINEARITY
ADJUST
@1/2 FS
R8
49.9k
10F
100
RTD
R4
100
00286
-0
42
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.
1
3
2
8
4
12V
+
REF02EZ
12V
2
6
4
D1
1N4148
5V
+
0.1F
+
–
K-TYPE
THERMOCOUPLE
40.7V/°C
R4
5.62k
R3
53.6
R6
200
R2
2.74k
+
–
1/2
OP213
0V TO 10V
(0°C TO 1000°C)
10F
0.1F
R9
124k
R5
40.2k
R1
10.7k
R8
453
00286-
043
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.
*ALL RESISTORS ±0.1%, ±25ppm/°C.
+
–
1/2
OP213
1/2
OP213
5V TO 36V
GAIN =
+ 6
+
–
+
–
VOUT
*R4
10k
20k
RG
VIN
*R1
10k
*R2
10k
*R3
10k
*RG
(200 + 12.7)
00
28
6-
0
44
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.