Analog Devices AD595CQ, AD595CD, AD595AQ, AD595AD, AD595 Datasheet
...
a Monolithic Thermocouple Amplifiers
with Cold Junction Compensation
AD594/AD595
FEATURES
Pretrimmed for Type J (AD594) or Type K (AD595) Thermocouples
Can Be Used with Type T Thermocouple Inputs Low Impedance Voltage Output: 10 mV/8C
Built-In Ice Point Compensation
Wide Power Supply Range: +5 V to 615 V
Low Power: <1 mW typical Thermocouple Failure Alarm
Laser Wafer Trimmed to 18C Calibration Accuracy
Setpoint Mode Operation
Self-Contained Celsius Thermometer Operation High Impedance Differential Input
Side-Brazed DIP or Low Cost Cerdip
FUNCTIONAL BLOCK DIAGRAM
–IN |
–ALM |
+ALM |
V+ |
COMP |
VO |
FB |
14 |
13 |
12 |
11 |
10 |
9 |
8 |
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OVERLOAD |
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DETECT |
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AD594/AD595 |
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+A |
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G |
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ICE |
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POINT |
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+TC |
COMP. –TC |
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1 |
2 |
3 |
4 |
5 |
6 |
7 |
+IN |
+C |
+T |
COM |
–T |
–C |
V– |
PRODUCT DESCRIPTION
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 A, 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
REV. C
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
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.
PRODUCT HIGHLIGHTS
1.The AD594/AD595 provides cold junction compensation, amplification, and an output buffer in a single IC package.
2.Compensation, zero, and scale factor are all precalibrated by laser wafer trimming (LWT) of each IC chip.
3.Flexible pinout provides for operation as a setpoint controller or a stand-alone temperature transducer calibrated in degrees Celsius.
4.Operation at remote application sites is facilitated by low quiescent current and a wide supply voltage range +5 V to dual supplies spanning 30 V.
5.Differential input rejects common-mode noise voltage on the thermocouple leads.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 |
World Wide Web Site: http://www.analog.com |
Fax: 781/326-8703 |
© Analog Devices, Inc., 1999 |
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(@ +258C and VS = 5 V, Type J (AD594), Type K (AD595) Thermocouple, |
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AD594/AD595–SPECIFICATIONS unless otherwise noted) |
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Model |
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AD594A |
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AD594C |
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AD595A |
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AD595C |
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Min |
Typ |
Max |
Min |
Typ |
Max |
Min |
Typ |
Max |
Min |
Typ |
Max |
Units |
ABSOLUTE MAXIMUM RATING |
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+VS to –VS |
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36 |
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36 |
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36 |
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36 |
Volts |
Common-Mode Input Voltage |
–VS – 0.15 |
+VS |
–VS – 0.15 |
+VS |
–VS – 0.15 |
+VS |
–VS – 0.15 |
+VS |
Volts |
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Differential Input Voltage |
–VS |
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+VS |
–VS |
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+VS |
–VS |
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+VS |
–VS |
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+VS |
Volts |
Alarm Voltages |
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+ALM |
–VS |
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–VS + 36 |
–VS |
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–VS + 36 |
–VS |
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–VS + 36 |
–VS |
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–VS + 36 |
Volts |
–ALM |
–VS |
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+VS |
–VS |
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+VS |
–VS |
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+VS |
–VS |
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+VS |
Volts |
Operating Temperature Range |
–55 |
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+125 |
–55 |
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+125 |
–55 |
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+125 |
–55 |
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+125 |
°C |
Output Short Circuit to Common |
Indefinite |
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Indefinite |
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Indefinite |
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Indefinite |
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TEMPERATURE MEASUREMENT |
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(Specified Temperature Range |
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0°C to +50°C) |
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Calibration Error at +25°C1 |
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63 |
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61 |
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63 |
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61 |
°C |
Stability vs. Temperature2 |
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60.05 |
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60.025 |
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60.05 |
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60.025 |
°C/°C |
Gain Error |
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61.5 |
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60.75 |
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61.5 |
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60.75 |
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Nominal Transfer Function |
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10 |
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10 |
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10 |
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10 |
mV/°C |
AMPLIFIER CHARACTERISTICS |
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Closed Loop Gain3 |
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193.4 |
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193.4 |
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247.3 |
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247.3 |
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Input Offset Voltage |
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(Temperature in °C) × |
(Temperature in °C) × |
(Temperature in °C) × |
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(Temperature in °C) × |
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51.70 µV/°C |
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51.70 µV/°C |
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40.44 µV/°C |
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40.44 µV/°C |
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µV |
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Input Bias Current |
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0.1 |
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0.1 |
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0.1 |
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0.1 |
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µA |
Differential Input Range |
–10 |
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+50 |
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–10 |
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+50 |
–10 |
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+50 |
mV |
Common-Mode Range |
–VS – 0.15 |
–VS – 4 |
–VS – 0.15 |
–VS – 4 |
–VS – 0.15 |
–VS – 4 |
–VS – 0.15 |
–VS – 4 |
Volts |
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Common-Mode Sensitivity – RTO |
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10 |
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10 |
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10 |
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10 |
mV/V |
Power Supply Sensitivity – RTO |
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10 |
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10 |
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10 |
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10 |
mV/V |
Output Voltage Range |
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Dual Supply |
–VS + 2.5 |
+VS – 2 |
–VS + 2.5 |
+VS – 2 |
–VS + 2.5 |
+VS – 2 |
–VS + 2.5 |
+VS – 2 |
Volts |
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Single Supply |
0 |
±5 |
+VS – 2 |
0 |
±5 |
–VS – 2 |
0 |
±5 |
+VS + 2 |
0 |
±5 |
+VS – 2 |
Volts |
Usable Output Current4 |
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mA |
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3 dB Bandwidth |
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15 |
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15 |
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15 |
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15 |
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kHz |
ALARM CHARACTERISTICS |
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VCE(SAT) at 2 mA |
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0.3 |
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0.3 |
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0.3 |
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0.3 |
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Volts |
Leakage Current |
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61 |
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61 |
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61 |
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61 |
µA max |
Operating Voltage at – ALM |
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+VS – 4 |
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+VS – 4 |
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+VS – 4 |
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+VS – 4 |
Volts |
Short Circuit Current |
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20 |
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20 |
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20 |
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20 |
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mA |
POWER REQUIREMENTS |
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Specified Performance |
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+VS = 5, –VS = 0 |
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+VS = 5, –VS = 0 |
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+VS = 5, –VS = 0 |
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+VS = 5, –VS = 0 |
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Volts |
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Operating5 |
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+VS to –VS ≤ 30 |
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+VS to –VS ≤ 30 |
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+VS to –VS ≤ 30 |
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+VS to –VS ≤ 30 |
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Volts |
Quiescent Current (No Load) |
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+VS |
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160 |
300 |
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160 |
300 |
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160 |
300 |
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160 |
300 |
µA |
–VS |
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100 |
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100 |
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100 |
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100 |
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µA |
PACKAGE OPTION |
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TO-116 (D-14) |
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AD594AD |
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AD594CD |
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AD595AD |
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AD595CD |
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Cerdip (Q-14) |
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AD594AQ |
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AD594CQ |
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AD595AQ |
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AD595CQ |
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NOTES
1Calibrated for minimum error at +25°C using a thermocouple sensitivity of 51.7 µV/°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.
2Defined as the slope of the line connecting the AD594/AD595 errors measured at 0°C and 50°C ambient temperature. 3Pin 8 shorted to Pin 9.
4Current Sink Capability in single supply configuration is limited to current drawn to ground through a 50 kΩ resistor at output voltages below 2.5 V. 5–VS must not exceed –16.5 V.
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.
INTERPRETING AD594/AD595 OUTPUT VOLTAGES
To achieve a temperature proportional output of 10 mV/°C and accurately compensate for the reference junction over the rated operating range of the circuit, the AD594/AD595 is gain trimmed to match the transfer characteristic of J and K type thermocouples at 25°C. For a type J output in this temperature range the TC is 51.70 µV/°C, while for a type K it is 40.44 µV/°C. The resulting gain for the AD594 is 193.4 (10 mV/°C divided by 51.7 µV/°C) and for the AD595 is 247.3 (10 mV/°C divided by 40.44 µV/°C). In addition, an absolute accuracy trim induces an input offset to the output amplifier characteristic of 16 µV for the AD594 and 11 µV for the AD595. This offset arises because the AD594/ AD595 is trimmed for a 250 mV output while applying a 25°C thermocouple input.
Because a thermocouple output voltage is nonlinear with respect to temperature, and the AD594/AD595 linearly amplifies the
compensated signal, the following transfer functions should be used to determine the actual output voltages:
AD594 output = (Type J Voltage + 16 µV) × 193.4 AD595 output = (Type K Voltage + 11 µV) × 247.3 or conversely:
Type J voltage = (AD594 output/193.4) – 16 µV Type K voltage = (AD595 output/247.3) – 11 µV
Table I lists the ideal AD594/AD595 output voltages as a function of Celsius temperature for type J and K ANSI standard thermocouples, with the package and reference junction at 25°C. As is normally the case, these outputs are subject to calibration, gain and temperature sensitivity errors. Output values for intermediate temperatures can be interpolated, or calculated using the output equations and ANSI thermocouple voltage tables referred to zero degrees Celsius. Due to a slight variation in alloy content between ANSI type J and DIN FE-CUNI
–2– |
REV. C |
AD594/AD595
Table I. Output Voltage vs. Thermocouple Temperature (Ambient +25°C, VS = –5 V, +15 V)
Thermocouple |
Type J |
AD594 |
Type K |
AD595 |
Temperature |
Voltage |
Output |
Voltage |
Output |
°C |
mV |
mV |
mV |
mV |
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–200 |
–7.890 |
–1523 |
–5.891 |
–1454 |
–180 |
–7.402 |
–1428 |
–5.550 |
–1370 |
–160 |
–6.821 |
–1316 |
–5.141 |
–1269 |
–140 |
–6.159 |
–1188 |
–4.669 |
–1152 |
–120 |
–5.426 |
–1046 |
–4.138 |
–1021 |
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–100 |
–4.632 |
–893 |
–3.553 |
–876 |
–80 |
–3.785 |
–729 |
–2.920 |
–719 |
–60 |
–2.892 |
–556 |
–2.243 |
–552 |
–40 |
–1.960 |
–376 |
–1.527 |
–375 |
–20 |
–.995 |
–189 |
–.777 |
–189 |
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–10 |
–.501 |
–94 |
–.392 |
–94 |
0 |
0 |
3.1 |
0 |
2.7 |
10 |
.507 |
101 |
.397 |
101 |
20 |
1.019 |
200 |
.798 |
200 |
25 |
1.277 |
250 |
1.000 |
250 |
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30 |
1.536 |
300 |
1.203 |
300 |
40 |
2.058 |
401 |
1.611 |
401 |
50 |
2.585 |
503 |
2.022 |
503 |
60 |
3.115 |
606 |
2.436 |
605 |
80 |
4.186 |
813 |
3.266 |
810 |
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100 |
5.268 |
1022 |
4.095 |
1015 |
120 |
6.359 |
1233 |
4.919 |
1219 |
140 |
7.457 |
1445 |
5.733 |
1420 |
160 |
8.560 |
1659 |
6.539 |
1620 |
180 |
9.667 |
1873 |
7.338 |
1817 |
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200 |
10.777 |
2087 |
8.137 |
2015 |
220 |
11.887 |
2302 |
8.938 |
2213 |
240 |
12.998 |
2517 |
9.745 |
2413 |
260 |
14.108 |
2732 |
10.560 |
2614 |
280 |
15.217 |
2946 |
11.381 |
2817 |
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300 |
16.325 |
3160 |
12.207 |
3022 |
320 |
17.432 |
3374 |
13.039 |
3227 |
340 |
18.537 |
3588 |
13.874 |
3434 |
360 |
19.640 |
3801 |
14.712 |
3641 |
380 |
20.743 |
4015 |
15.552 |
3849 |
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400 |
21.846 |
4228 |
16.395 |
4057 |
420 |
22.949 |
4441 |
17.241 |
4266 |
440 |
24.054 |
4655 |
18.088 |
4476 |
460 |
25.161 |
4869 |
18.938 |
4686 |
480 |
26.272 |
5084 |
19.788 |
4896 |
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Thermocouple |
Type J |
AD594 |
Type K |
AD595 |
Temperature |
Voltage |
Output |
Voltage |
Output |
°C |
mV |
mV |
mV |
mV |
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500 |
27.388 |
5300 |
20.640 |
5107 |
520 |
28.511 |
5517 |
21.493 |
5318 |
540 |
29.642 |
5736 |
22.346 |
5529 |
560 |
30.782 |
5956 |
23.198 |
5740 |
580 |
31.933 |
6179 |
24.050 |
5950 |
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600 |
33.096 |
6404 |
24.902 |
6161 |
620 |
34.273 |
6632 |
25.751 |
6371 |
640 |
35.464 |
6862 |
26.599 |
6581 |
660 |
36.671 |
7095 |
27.445 |
6790 |
680 |
37.893 |
7332 |
28.288 |
6998 |
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700 |
39.130 |
7571 |
29.128 |
7206 |
720 |
40.382 |
7813 |
29.965 |
7413 |
740 |
41.647 |
8058 |
30.799 |
7619 |
750 |
42.283 |
8181 |
31.214 |
7722 |
760 |
– |
– |
31.629 |
7825 |
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780 |
– |
– |
32.455 |
8029 |
800 |
– |
– |
33.277 |
8232 |
820 |
– |
– |
34.095 |
8434 |
840 |
– |
– |
34.909 |
8636 |
860 |
– |
– |
35.718 |
8836 |
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880 |
– |
– |
36.524 |
9035 |
900 |
– |
– |
37.325 |
9233 |
920 |
– |
– |
38.122 |
9430 |
940 |
– |
– |
38.915 |
9626 |
960 |
– |
– |
39.703 |
9821 |
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980 |
– |
– |
40.488 |
10015 |
1000 |
– |
– |
41.269 |
10209 |
1020 |
– |
– |
42.045 |
10400 |
1040 |
– |
– |
42.817 |
10591 |
1060 |
– |
– |
43.585 |
10781 |
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1080 |
– |
– |
44.439 |
10970 |
1100 |
– |
– |
45.108 |
11158 |
1120 |
– |
– |
45.863 |
11345 |
1140 |
– |
– |
46.612 |
11530 |
1160 |
– |
– |
47.356 |
11714 |
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1180 |
– |
– |
48.095 |
11897 |
1200 |
– |
– |
48.828 |
12078 |
1220 |
– |
– |
49.555 |
12258 |
1240 |
– |
– |
50.276 |
12436 |
1250 |
– |
– |
50.633 |
12524 |
thermocouples Table I should not be used in conjunction with European standard thermocouples. Instead the transfer function given previously and a DIN thermocouple table should be used. ANSI type K and DIN NICR-NI thermocouples are composed
CONSTANTAN |
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+5V |
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10mV/8C |
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(ALUMEL) |
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14 |
13 |
12 |
11 |
10 |
9 |
8 |
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OVERLOAD |
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DETECT |
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AD594/ |
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+A |
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AD595 |
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G |
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G |
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ICE |
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POINT |
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+TC |
COMP. –TC |
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IRON |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
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(CHROMEL) |
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COMMON |
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Figure 1. Basic Connection, Single Supply Operation
of identical alloys and exhibit similar behavior. The upper temperature limits in Table I are those recommended for type J and type K thermocouples by the majority of vendors.
SINGLE AND DUAL SUPPLY CONNECTIONS
The AD594/AD595 is a completely self-contained thermocouple conditioner. Using a single +5 V supply the interconnections shown in Figure 1 will provide a direct output from a type J thermocouple (AD594) or type K thermocouple (AD595) measuring from 0°C to +300°C.
Any convenient supply voltage from +5 V to +30 V may be used, with self-heating errors being minimized at lower supply levels. In the single supply configuration the +5 V supply connects to Pin 11 with the V– connection at Pin 7 strapped to power and signal common at Pin 4. The thermocouple wire inputs connect to Pins 1 and 14 either directly from the measuring point or through intervening connections of similar thermocouple wire type. When the alarm output at Pin 13 is not used it should be connected to common or –V. The precalibrated feedback network at Pin 8 is tied to the output at Pin 9 to provide a 10 mV/°C nominal temperature transfer characteristic.
By using a wider ranging dual supply, as shown in Figure 2, the AD594/AD595 can be interfaced to thermocouples measuring both negative and extended positive temperatures.
REV. C |
–3– |
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