High_temperature_thermometer_with_analog_and_digital_outputs

Published:2009/7/24 3:01:00 Author:Jessie | From:SeekIC

Fig. 13-36 In this circuit, an LF347 is used to signal condition a platinum RTD and provide simultaneous analog and frequency outputs. These outputs are accurate to ±1℃ over a range of300 to 600℃ (572 to 1112°F). Although the circuit maintains linearity over a much wider range, the nonlinear response of the RTD mover wide range is the limiting factor, as shown in the graph of Fig. 13-36B. To calibrate the thermometer, substitute a high-quality decade box (General Radio 1432-KL) for the sensor. Alternately adjust the zero (300℃) and full-scale (600℃) potentiometers for the resistance values noted in Fig. 13-36B until the A2 output is calibrated (3 to 6 V). Then, adjust the 200-kΩ frequency trim so that the output frequency corresponds to the value at the A2 output (300 Hz at the frequency output for 3 V at the analog output). National Semiconductor, Linear Applications Handbook 1991,p. 729.730.



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