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AMP04FS-REEL Datasheet(PDF) 10 Page - AVAGO TECHNOLOGIES LIMITED |
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AMP04FS-REEL Datasheet(HTML) 10 Page - AVAGO TECHNOLOGIES LIMITED |
10 / 16 page AMP04 REV. B –10– 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. R10 100 R2 26.7k RSENSE 1k VOUT FULL-SCALE ADJ 0 4.00V (0 C TO 400 C) LINEARITY ADJ. (@1/2 FS) NOTES: ALL RESISTORS 0.5%, 25 PPM/ C ALL POTENTIOMETERS 25 PPM/ C AMP04 R8 383 R9 50 C1 0.47 F 1 7 3 2 4 5 8 6 1/2 OP295 1/2 OP295 R1 26.7k 500 R4 100 R6 11.5k R5 1.02k OUT REF43 IN GND 2.5V R7 121k 50k 4 5 6 8 7 5V 2 5V C2 0.1 F C3 0.1 F RTD 100 0.202V 6 4 1 2 3 R3 BALANCE 5V A B 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 k Ω 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. RSENSE 20 U1 AMP04 5k 10-TURN 2.49k 1 7 3 2 4 5 8 6 U2 OP90 50mV FS 0.22 F 97.6k 3 2 B 976k 50k HP 5082-2810 220pF 4 6 100k 5% 2k 5% T1P29A 0.1 F 5.00V OUT REF02 N GND U3 1N4002 4mA NULL 13.3k 15.8k 3500 STRAIN GAGE BRIDGE 7 20mA SPAN 6 2 4 +VS 12V TO 36V RLOAD 100 4-20mA INULL + ISPAN UNLESS OTHERWISE SPECIFIED, ALL RESISTORS 1% OR BETTER POTENTIOMETER < 50 PPM/ C Figure 12. Precision 4-20 mA Loop Transmitter Features Noninteractive Trims |
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