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The AD594/AD595 is a complete instrumentaTIon amplifier andthermocouple cold juncTIon compensator on a monolithic chip.It combines an ice point reference with a precalibrated amplifierto produce a high level (10 mV/°C) output directly from a thermocouplesignal. Pin-strapping opTIons allow it to be used as alinear amplifier-compensator or as a switched output setpointcontroller using either fixed or remote setpoint control. It canbe used to amplify its compensaTIon voltage directly, therebyconverting it to a stand-alone Celsius transducer with a lowimpedance voltage output.The AD594/AD595 includes a thermocouple failure alarm thatindicates if one or both thermocouple leads become open. Thealarm output has a flexible format which includes TTL drivecapability.The AD594/AD595 can be powered from a single ended supply(including +5 V) and by including a negative supply, temperaturesbelow 0°C can be measured. To minimize self-heating, anunloaded AD594/AD595 will typically operate with a total supplycurrent 160 mA, but is also capable of delivering in excess of±5 mA to a load.The AD594 is precalibrated by laser wafer trimming to matchthe characteristic of type J (iron-constantan) thermocouples andthe AD595 is laser trimmed for type K (chromel-alumel) inputs.The temperature transducer voltages and gain control resistorsare available at the package pins so that the circuit can berecalibrated for the thermocouple types by the addition of twoor three resistors. These terminals also allow more precise calibrationfor both thermocouple and thermometer applications.The AD594/AD595 is available in two performance grades. TheC and the A versions have calibration accuracies of ±1°C and±3°C, respectively. Both are designed to be used from 0°C to+50°C, and are available in 14-pin, hermetically sealed, sidebrazedceramic DIPs as well as low cost cerdip packages.
