The AD594/AD595 is a complete instrumentation amplifier and
thermocouple cold junction compensator on a monolithic chip.
It combines an ice point reference with a precalibrated amplifier
to produce a high level (10 mV/°C) output directly from a thermocouple
signal. Pin-strapping options allow it to be used as a
linear amplifier-compensator or as a switched output setpoint
controller using either fixed or remote setpoint control. It can
be used to amplify its compensation voltage directly, thereby
converting it to a stand-alone Celsius transducer with a low
impedance voltage output.
The AD594/AD595 includes a thermocouple failure alarm that
indicates if one or both thermocouple leads become open. The
alarm output has a flexible format which includes TTL drive
capability.
The AD594/AD595 can be powered from a single ended supply
(including +5 V) and by including a negative supply, temperatures
below 0°C can be measured. To minimize self-heating, an
unloaded AD594/AD595 will typically operate with a total supply
current 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 match
the characteristic of type J (iron-constantan) thermocouples and
the AD595 is laser trimmed for type K (chromel-alumel) inputs.
The temperature transducer voltages and gain control resistors
are available at the package pins so that the circuit can be
recalibrated for the thermocouple types by the addition of two
or three resistors. These terminals also allow more precise calibration
for both thermocouple and thermometer applications.
The AD594/AD595 is available in two performance grades. The
C 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, sidebrazed
ceramic DIPs as well as low cost cerdip packages.