The ADT70 provides excitation and signal conditioning for resistance-temperature devices (RTDs). It is ideally suited for 1 kW Platinum RTDs (PRTDs), allowing a very wide range of temperature measurement. It can also easily interface to 100 W PRTDs. Using a remote, low cost thin-film PRTD, the ADT70 can measure temperature in the range of 50°C to +500°C. With high performance platinum elements, the temperature change can be extended to 1000°C. Accuracy of the ADT70 and PRTD system over a 200°C to +1000°C temperature range heavily depends on the quality of the PRTD. Typically the ADT70 will introduce an error of only ±1°C over the transducer's temperature range, and the error may be trimmed to zero at a single calibration point.
The ADT70 consists of two matched 1 mA (nominal) current sources for transducer and reference resistor excitation, a precision rail-to-rail output instrumentation amplifier, a 2.5 V reference\ and an uncommitted rail-to-rail output op amp. The ADT70 includes a shutdown function for battery powered equipment, which reduces the quiescent current from 4 mA to less than 10ÊmA. The ADT70 operates from either single +5 V or ±5 V supplies. Gain or full-scale range for the PRTD and ADT70 system is set by a precision external resistor connected to the instrumentation amplifier. The uncommitted op amp may be used for scaling the internal voltage reference, providing a "PRTD open" signal or "over-temperature" warning, a heater switching signal, or other external conditioning determined by the user.
The ADT70 is specified for operation from 240°C to 1125°C and is available in 20-lead DIP and SO packages.
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