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AD592 数据表(PDF) 7 Page - Analog Devices |
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AD592 数据表(HTML) 7 Page - Analog Devices |
7 / 8 page AD592 REV. A –7– The circuit shown can be optimized for any ambient tempera- ture range or thermocouple type by simply selecting the correct value for the scaling resistor – R. The AD592 output (1 µA/K) times R should approximate the line best fit to the thermocouple curve (slope in V/ °C) over the most likely ambient temperature range. Additionally, the output sensitivity can be chosen by selecting the resistors RG1 and RG2 for the desired noninverting gain. The offset adjustment shown simply references the AD592 to °C. Note that the TC’s of the reference and the resistors are the primary contributors to error. Temperature rejection of 40 to 1 can be easily achieved using the above technique. Although the AD592 offers a noise immune current output, it is not compatible with process control/industrial automation cur- rent loop standards. Figure 12 is an example of a temperature to 4–20 mA transmitter for use with 40 V, 1 k Ω systems. In this circuit the 1 µA/K output of the AD592 is amplified to 1 mA/ °C and offset so that 4 mA is equivalent to 17°C and 20 mA is equivalent to 33 °C. Rt is trimmed for proper reading at an intermediate reference temperature. With a suitable choice of resistors, any temperature range within the operating limits of the AD592 may be chosen. AD592 AD581 35.7k Ω 10mV/oC 10k Ω 12.7k Ω 5k Ω 500 Ω +20V –20V VT 10 Ω C RT 5k Ω 1mA/oC 208 17 °C ≈ 4mA 33 °C ≈ 20µA Figure 12. Temperature to 4–20 mA Current Transmitter Reading temperature with an AD592 in a microprocessor based system can be implemented with the circuit shown in Figure 13. AD1403 950 Ω 9k Ω 1k Ω 100 Ω +5V AD592 SPAN TRIM CENTER POINT TRIM FORMAT BPO/UPO 200 Ω µP CONTROL GND VIN HI VI HI N VI LO N VI LO N 8 BITS OUT AD670 ADCPORT R/W CS CE VCC Figure 13. Temperature to Digital Output By using a differential input A/D converter and choosing the current to voltage conversion resistor correctly, any range of temperatures (up to the 130 °C span the AD592 is rated for) centered at any point can be measured using a minimal number of components. In this configuration the system will resolve up to 1 °C. A variable temperature controlling thermostat can easily be built using the AD592 in the circuit of Figure 14. AD592 10k Ω RHYST RPULL-UP +15V COMPARATOR (OPTIONAL) C RHIGH 62.7k Ω RSET 10k Ω C TEMP > SETPOINT OUTPUT HIGH TEMP < SETPOINT OUTPUT LOW RLOW 27.3k Ω AD581 Figure 14. Variable Temperature Thermostat RHIGH and RLOW determine the limits of temperature controlled by the potentiometer RSET. The circuit shown operates over the full temperature range (–25 °C to +105°C) the AD592 is rated for. The reference maintains a constant set point voltage and insures that approximately 7 V appears across the sensor. If it is necessary to guardband for extraneous noise hysteresis can be added by tying a resistor from the output to the ungrounded end of RLOW. Multiple remote temperatures can be measured using several AD592s with a CMOS multiplexer or a series of 5 V logic gates because of the device’s current-mode output and supply-voltage compliance range. The on-resistance of a FET switch or output impedance of a gate will not affect the accuracy, as long as 4 V is maintained across the transducer. MUXs and logic driving circuits should be chosen to minimize leakage current related errors. Figure 15 illustrates a locally controlled MUX switching the signal current from several remote AD592s. CMOS or TTL gates can also be used to switch the AD592 supply voltages, with the multiplexed signal being transmitted over a single twisted pair to the load. AD7501 D E C O D E R / D R I V E R T8 T2 T1 REMOTE AD592s S1 S2 S8 EN TTL DTL TO CMOS I/O CHANNEL SELECT +15V –15V VOUT 10k Ω Figure 15. Remote Temperature Multiplexing |
类似零件编号 - AD592 |
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类似说明 - AD592 |
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