Monolithic Thermocouple Amplifiers a with Cold Junction Compensation AD594/AD595 FEATURES FUNCTIONAL BLOCK DIAGRAM Pretrimmed for Type J (AD594) or Type K (AD595) Thermocouples IN ALM +ALM V+ COMP VO FB 14 13 12 11 10 9 8 Can Be Used with Type T Thermocouple Inputs Low Impedance Voltage Output: 10 mV/8C OVERLOAD DETECT Built-In Ice Point Compensation Wide Power Supply Range: +5 V to 615 V AD594/AD595 +A Low Power: <1 mW typical Thermocouple Failure Alarm Laser Wafer Trimmed to 18C Calibration Accuracy ICE G G POINT Setpoint Mode Operation TC COMP. +TC Self-Contained Celsius Thermometer Operation High Impedance Differential Input 1 2 345 6 7 Side-Brazed DIP or Low Cost Cerdip +IN +C +T COM T C V PRODUCT DESCRIPTION are available at the package pins so that the circuit can be The AD594/AD595 is a complete instrumentation amplifier and recalibrated for the thermocouple types by the addition of two thermocouple cold junction compensator on a monolithic chip. or three resistors. These terminals also allow more precise cali- It combines an ice point reference with a precalibrated amplifier bration for both thermocouple and thermometer applications. to produce a high level (10 mV/ C) output directly from a ther- The AD594/AD595 is available in two performance grades. The mocouple signal. Pin-strapping options allow it to be used as a C and the A versions have calibration accuracies of 1 C and linear amplifier-compensator or as a switched output setpoint 3 C, respectively. Both are designed to be used from 0 C to controller using either fixed or remote setpoint control. It can +50 C, and are available in 14-pin, hermetically sealed, side- be used to amplify its compensation voltage directly, thereby brazed ceramic DIPs as well as low cost cerdip packages. converting it to a stand-alone Celsius transducer with a low impedance voltage output. PRODUCT HIGHLIGHTS The AD594/AD595 includes a thermocouple failure alarm that 1. The AD594/AD595 provides cold junction compensation, indicates if one or both thermocouple leads become open. The amplification, and an output buffer in a single IC package. alarm output has a flexible format which includes TTL drive 2. Compensation, zero, and scale factor are all precalibrated by capability. laser wafer trimming (LWT) of each IC chip. The AD594/AD595 can be powered from a single ended supply 3. Flexible pinout provides for operation as a setpoint control- (including +5 V) and by including a negative supply, tempera- ler or a stand-alone temperature transducer calibrated in tures below 0 C can be measured. To minimize self-heating, an degrees Celsius. unloaded AD594/AD595 will typically operate with a total sup- 4. Operation at remote application sites is facilitated by low ply current 160 m A, but is also capable of delivering in excess of quiescent current and a wide supply voltage range +5 V to 5 mA to a load. dual supplies spanning 30 V. The AD594 is precalibrated by laser wafer trimming to match 5. Differential input rejects common-mode noise voltage on the the characteristic of type J (iron-constantan) thermocouples and thermocouple leads. the AD595 is laser trimmed for type K (chromel-alumel) inputs. The temperature transducer voltages and gain control resistors REV. C Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. use, nor for any infringements of patents or other rights of third parties Tel: 781/329-4700 World Wide Web Site: ( +258C and V = 5 V, Type J (AD594), Type K (AD595) Thermocouple, S unless otherwise noted) AD594/AD595SPECIFICATIONS Model AD594A AD594C AD595A AD595C Min Typ Max Min Typ Max Min Typ Max Min Typ Max Units ABSOLUTE MAXIMUM RATING +V to V 36 36 36 36 Volts S S Common-Mode Input Voltage V 0.15 +V V 0.15 +V V 0.15 +V V 0.15 +V Volts S S S S S S S S Differential Input Voltage V +V V +V V +V V +V Volts S S S S S S S S Alarm Voltages +ALM V V + 36 V V + 36 V V + 36 V V + 36 Volts S S S S S S S S ALM V +V V +V V +V V +V Volts S S S S S S S S Operating Temperature Range 55 +125 55 +125 55 +125 55 +125 C Output Short Circuit to Common Indefinite Indefinite Indefinite Indefinite TEMPERATURE MEASUREMENT (Specified Temperature Range 0 C to +50 C) 1 Calibration Error at +25 C 63 61 63 61 C 2 Stability vs. Temperature 60.05 60.025 60.05 60.025 C/ C Gain Error 61.5 60.75 61.5 60.75 % Nominal Transfer Function 10 10 10 10 mV/ C AMPLIFIER CHARACTERISTICS 3 Closed Loop Gain 193.4 193.4 247.3 247.3 Input Offset Voltage (Temperature in C) (Temperature in C) (Temperature in C) (Temperature in C) 51.70 m V/ C 51.70 m V/ C 40.44 m V/ C 40.44 m V/ C m V Input Bias Current 0.1 0.1 0.1 0.1 m A Differential Input Range 10 +50 10 +50 10 +50 mV Common-Mode Range V 0.15 V 4 V 0.15 V 4 V 0.15 V 4 V 0.15 V 4 Volts S S S S S S S S Common-Mode Sensitivity RTO 10 10 10 10 mV/V Power Supply Sensitivity RTO 10 10 10 10 mV/V Output Voltage Range Dual Supply V + 2.5 +V 2 V + 2.5 +V 2 V + 2.5 +V 2 V + 2.5 +V 2 Volts S S S S S S S S Single Supply 0 +V 2 0 V 2 0 +V + 2 0 +V 2 Volts S S S S 4 Usable Output Current 5 5 5 5mA 3 dB Bandwidth 15 15 15 15 kHz ALARM CHARACTERISTICS V at 2 mA 0.3 0.3 0.3 0.3 Volts CE(SAT) Leakage Current 61 61 61 61 m A max Operating Voltage at ALM +V 4 +V 4 +V 4 +V 4 Volts S S S S Short Circuit Current 20 20 20 20 mA POWER REQUIREMENTS Specified Performance +V = 5, V = 0 +V = 5, V = 0 +V = 5, V = 0 +V = 5, V = 0 Volts S S S S S S S S 5 Operating +V to V 30 +V to V 30 +V to V 30 +V to V 30 Volts S S S S S S S S Quiescent Current (No Load) +V 160 300 160 300 160 300 160 300 m A S V 100 100 100 100 m A S PACKAGE OPTION TO-116 (D-14) AD594AD AD594CD AD595AD AD595CD Cerdip (Q-14) AD594AQ AD594CQ AD595AQ AD595CQ NOTES 1 Calibrated for minimum error at +25 C using a thermocouple sensitivity of 51.7 m V/ C. Since a J type thermocouple deviates from this straight line approximation, the AD594 will normally read 3.1 mV when the measuring junction is at 0 C. The AD595 will similarly read 2.7 mV at 0 C. 2 Defined as the slope of the line connecting the AD594/AD595 errors measured at 0 C and 50 C ambient temperature. 3 Pin 8 shorted to Pin 9. 4 Current Sink Capability in single supply configuration is limited to current drawn to ground through a 50 kW resistor at output voltages below 2.5 V. 5 V must not exceed 16.5 V. S Specifications shown in boldface are tested on all production units at final electrical test. Results from those tests are used to calculate outgoing quality levels. All min and max specifications are guaranteed, although only those shown in boldface are tested on all production units. Specifications subject to change without notice. compensated signal, the following transfer functions should be INTERPRETING AD594/AD595 OUTPUT VOLTAGES used to determine the actual output voltages: To achieve a temperature proportional output of 10 mV/ C and accurately compensate for the reference junction over the rated AD594 output = (Type J Voltage + 16 m V) 193.4 operating range of the circuit, the AD594/AD595 is gain trimmed AD595 output = (Type K Voltage + 11 m V) 247.3 or conversely: to match the transfer characteristic of J and K type thermocouples Type J voltage = (AD594 output/193.4) 16 m V at 25 C. For a type J output in this temperature range the TC is Type K voltage = (AD595 output/247.3) 11 m V 51.70 m V/ C, while for a type K it is 40.44 m V/ C. The resulting Table I lists the ideal AD594/AD595 output voltages as a func- gain for the AD594 is 193.4 (10 mV/ C divided by 51.7 m V/ C) tion of Celsius temperature for type J and K ANSI standard and for the AD595 is 247.3 (10 mV/ C divided by 40.44 m V/ C). thermocouples, with the package and reference junction at In addition, an absolute accuracy trim induces an input offset to 25 C. As is normally the case, these outputs are subject to cali- the output amplifier characteristic of 16 m V for the AD594 and bration, gain and temperature sensitivity errors. Output values 11 m V for the AD595. This offset arises because the AD594/ for intermediate temperatures can be interpolated, or calculated AD595 is trimmed for a 250 mV output while applying a 25 C using the output equations and ANSI thermocouple voltage thermocouple input. tables referred to zero degrees Celsius. Due to a slight variation Because a thermocouple output voltage is nonlinear with respect in alloy content between ANSI type J and DIN FE-CUNI to temperature, and the AD594/AD595 linearly amplifies the 2 REV. C