AMP04 查看數據表（PDF） - Analog Devices
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AMP04 Datasheet PDF : 17 Pages
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AMP04
APPLICATION CIRCUITS
Low Power Precision Single Supply RTD Amplifier
Figure 11 shows a linearized RTD amplifier that is powered
from a single 5 volt supply. However, the circuit will work up to
36 volts without modification. The RTD is excited by a 100 µA
constant current that is regulated by amplifier A (OP295). The
0.202 volts reference voltage used to generate the constant current
is divided down from the 2.500 volt reference. The AMP04 ampli-
fies the bridge output to a 10 mV/°C output coefficient.
R9
5V
50⍀
R3
BALANCE
C3
0.1F
R8
R10
383⍀ 100⍀
R1 500⍀ R2
26.7k⍀
26.7k⍀
3
RTD
100⍀
2
R4
1
100⍀
1/2
A
OP295
2
3
R7
121k⍀
R5
1.02k⍀
0.202V
R6
11.5k⍀
7
1
8
AMP04 6
5
4
5V
8
6
7 1/2 B
OP295
5
4
RSENSE
1k⍀
2.5V 6
OUT
REF43
IN 2
GND
4
5V
C2
0.1F
FULL-SCALE
ADJ
C1
0.47F
VOUT
0 4.00V
(0؇C TO 400؇C)
50k⍀
LINEARITY
ADJ.
(@1/2 FS)
NOTES: ALL RESISTORS ؎0.5%, ؎25 PPM/؇C
ALL POTENTIOMETERS ؎25 PPM/؇C
Figure 11. Precision Single Supply RTD Thermometer
Amplifier
The RTD is linearized by feeding a portion of the signal back to
the reference circuit, increasing the reference voltage as the
temperature increases. When calibrated properly, the RTD’s
nonlinearity error will be canceled.
To calibrate, either immerse the RTD into a zero-degree ice
bath or substitute an exact 100 Ω resistor in place of the RTD.
Then adjust bridge BALANCE potentiometer R3 for a 0 volt
output. Note that a 0 volt output is also the negative output swing
limit of the AMP04 powered with a single supply. Therefore, be
sure to adjust R3 to first cause the output to swing positive and
then back off until the output just stops swinging negatively.
Next, set the LINEARITY ADJ potentiometer to the midrange.
Substitute an exact 247.04 Ω resistor (equivalent to 400°C
temperature) in place of the RTD. Adjust the FULL-SCALE
potentiometer for a 4.000 volts output.
Finally substitute a 175.84 Ω resistor (equivalent to 200°C
temperature), and adjust the LINEARITY ADJ potentiometer
for a 2.000 volts at the output. Repeat the full-scale and the
half-scale adjustments as needed.
When properly calibrated, the circuit achieves better than
± 0.5°C accuracy within a temperature measurement range
from 0°C to 400°C.
Precision 4-20 mA Loop Transmitter with Noninteractive Trim
Figure 12 shows a full bridge strain gage transducer amplifier
circuit that is powered off the 4-20 mA current loop. The AMP04
amplifies the bridge signal differentially and is converted to a
current by the output amplifier. The total quiescent current
drawn by the circuit, which includes the bridge, the amplifiers,
and the resistor biasing, is only a fraction of the 4 mA null
current that flows through the current-sense resistor RSENSE.
The voltage across RSENSE feeds back to the OP90’s input,
whose common-mode is fixed at the current summing reference
voltage, thus regulating the output current.
With no bridge signal, the 4 mA null is simply set up by the
50 kΩ NULL potentiometer plus the 976 kΩ resistors that
inject an offset that forces an 80 mV drop across RSENSE. At a
50 mV full-scale bridge voltage, the AMP04 amplifies the
voltage-to-current converter for a full-scale of 20 mA at the
output. Since the OP90’s input operates at a constant 0 volt
common-mode voltage, the null and the span adjustments do
not interact with one another. Calibration is simple and easy
with the NULL adjusted first, followed by SPAN adjust. The
entire circuit can be remotely placed, and powered from the
4-20 mA 2-wire loop.
3500⍀ STRAIN
GAGE BRIDGE
50mV
FS
U3
5.00V
4mA NULL
6 REF02 2
OUT
N
2.49k⍀
0.22F
3
7
1
5k⍀
U1 8
10-TURN 97.6k⍀
AMP04 6
2
5
4
20mA
SPAN
HP
5082-2810
50k⍀
GND
4
976k⍀
3
7
B
U2 6
OP90
2
4 220pF
2k⍀
5%
T1P29A
0.1F
1N4002
13.3k⍀
100k⍀
5%
+VS
12V TO 36V
UNLESS OTHERWISE SPECIFIED, ALL RESISTORS ؎1%
OR BETTER POTENTIOMETER < 50 PPM/؇C
15.8k⍀
RSENSE
20⍀
4-20mA
RLOAD
100⍀
INULL + ISPAN
Figure 12. Precision 4-20 mA Loop Transmitter Features Noninteractive Trims
–10–
REV. C
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