Sensor catalog - Watlow - #14

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Text version of the page
General Information
Thermocouple Types
Calibration types have been estab­lished by the American Society for Testing and Materials (ASTM) according to their temperature versus EMF characteristics in accordance with ITS-90, in standard or special tolerances.
Additionally, there are non-ASTM calibration types. These thermo­couples are made from tungsten and tungsten-rhenium alloys. Generally used for measuring higher temper­atures, they're a more economical alternative to the platinum and platinum alloy based noble metal thermocouples, but limited to use in inert and non-oxidizing atmospheres.
Application Hints
What do thermocouple letter designations mean?
Thermocouples are classified by calibration type because they have differing EMF (electromotive force) versus temperature curves. Some generate considerably more voltage at lower temperatures, while others do not begin to develop a significant voltage until subjected to high temperatures. Also, calibration types are designed to deliver as close to a straight line voltage curve inside their temperature application range as possible. This makes it easier for an instrument or temperature controller to correctly correlate the received voltage to a particular temperature.
Additionally, thermocouple calibration types have different levels of compatibility with different atmospheres. Chemical reaction between certain thermocouple alloys and the application atmosphere could cause metallurgy degradation, making another calibration type more suitable for sensor life and accuracy requirements.
Thermocouple
Useful/General
Type
Application Range
B
1370-1700°C (2500-3100°F)
C*
1650-2315°C (3000-4200°F)
E**
95-900°C (200-1650°F)
J
95-760°C (200-1400°F)
K**
95-1260°C (200-2300°F)
N
95-1260°C (200-2300°F)
R
870-1450°C (1600-2640°F)
S
980-1450°C (1800-2640°F)
T**
0-350°C (32-660°F)
''Not an ASTM E 230 symbol
**Also suitable for cryogenic applications from -200 to 0°C (-328 to 32°F)
Thermocouple Millivolts'/Temperature Curves
80
70
60
(A
|
50
40
30
20
10
5000
0
1000 2000 3000
Temperature (°F)
4000
'Millivolt values shown for C, R, S and B calibrations pertain to thermocouple calibrations only. RX, SX and BX constructions described in this catalog section are intended for use as extension wire only and will not exhibit the millivolt outputs shown.
''Not an ASTM E 230 Symbol—Tungsten 5 percent Rhenium/Tungsten 26 percent Rhenium.
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pageCatalog pdf di En 2012-02-06-11