Thermocouple Technical Reference Chart

Below are the ANSI and non-ANSI material specifications and recommended operating temperature ranges and application considerations. Ultimately, each thermocouple application is unique and the selection of a suitable thermocouple relies on many factors. The table below is for general guideline purposes. For assistance with specific application, please contact Ultra Electronics, Energy directly at Phone: 800.321.0796

ANSI CODED MATERIAL SPECIFICATIONS

TYPE CODE POSITIVE
LEG
NEGATIVE
LEG
RECOMMENDED
TEMP. RANGE
F(C) OF PROT. TC
APPLICATION INFORMATION
J Iron
ThermoKanthal JP
Constantan
Cupron
Advance
ThermoKanthal JN
32 to 1400°F
(0 to 760°C)
Suitable for vacuum, reducing or insert
atmospheres, oxidizing, atmosphere with reduced life. Iron oxidizes rapidly above 1000°F (538°C) so only heavy gauge wire is recommended for high temperature. Bare elements should not be exposed to sulphurous atmospheres above 1000°F (538°C)
K Chromel
Tophel
T1
ThermoKanthal KP
Alumel
Nial
T2
ThermoKanthal KN
32 to 2300°F
(0 to 1260°C)
Recommended for continuous oxidizing or neutral atmospheres. Mostly used above 1000°F (538°C). Subject to failure if exposed to sulphur. Preferential oxidation of chromium in positive leg at certain low oxygen concentrations causes ‘green rot’ and large negative calibration drifts most serious in the 1500-1900°F (816°C-1038°C) range. Ventilation or inert sealing of the protection tube can prevent this.
N Nicrosil
14.5% Chromium
1.4% Silicon
.1% Magnesium
Balance Nickel
Nisil
4.2% Silicon
.1% Magnesium
Balance Nickel
32 to 2300 °F
(0 to 1260°C)
 Can be used in applications where Type K elements have shorter life and stability problems due to oxidation and the development of ‘green rot’.
T Copper Constantan
Cupron
Advance
-300 to 700°F
(-184 to 371°C)
Useable in oxidizing, reducing or inert atmospheres. Sub-zero limits of error not established. Highest thermoelectric output of common calibrations.
E Chromel
Tophel
T1
ThermoKanthal KP
Constantan
Cupron
Advance
ThermoKanthal JN
32 to 1600°F
(0 to 871 °C)
Recommended for continuously oxidizing or inert atmospheres. Sub-zero limits of error not established. Highest thermoelectric output of common calibrations.
R Platinum- 13%
Rhodium
Platinum 1000 to 2700°F
(538 to 1482°C)
Recommended for high temperature. Must be protected with non-metallic protection tube and ceramic insulators. Continued high temperature usages causes grain growth which can lead to mechanical failure. Negative calibration drift caused by Rhodium diffusion to pure leg as well as from Rhodium volatilization. Type R is used in industry; Type S in the laboratory.
S Platinum- 10%
Rhodium
Platinum
B Platinum- 30%
Rhodium
Platinum- 6%
Rhodium
1600 to 3100°F
(871 to 1705 °C)
Same as R & S but output is lower. Also less susceptible to grain growth and drift.

 

NON-ANSI CODED MATERIAL SPECIFICATIONS

TYPE CODE POSITIVE
LEG
NEGATIVE
LEG
RECOMMENDED
TEMP. RANGE
F(C) OF PROT. TC
APPLICATION INFORMATION
C Tungsten-
5% Rhenium
(W-5% Re)
Tungsten-
26% Rhenium
(W-26% Re)
32 to 4200°F
(0 to 2315°C)
Very high temperature applications in inert or vacuum. Preferred over Tungsten/Tungsten-26% Rhenium because it is less brittle at low temperatures.
D Tungsten-
3% Rhenium
(W-3% Re)
Tungsten-
26% Rhenium
(W-26% Re)
32 to 4200°F
(0 to 2315°C)
The ductility of the W3Re leg is superior to pure Tungsten, but not as good as W5Re. This combination has highest output of the 3 common Tungsten Rhenium calibrations from 1860-4200°F.
G Tungsten (W) Tungsten-
26% Rhenium
(W-26% Re)
32 to 4200°F
(0 to 2315°C)
Very high temperature application in inert or vacuum. Heating to above 2192°F creates a loss of ductility at room temperature. This embrittlement creates mechanical weakness.
M Nickel-
18% Molybdenum
(Ni-18% Mo)
Nickel
(Ni-0.8% Co)
-58 to 2570°F
(-50 to 1410 °C)
High temperature applications in inert or vacuum atmosphere. Useful in many hydrogen applications. Continuous cycling causes excessive grain growth.
P Platinel 5355 Platinel 7674 32 to 2543 °F
(0 to 1395 °C)
Nobel metal combination which approximates Type K curve but has much improved oxidation resistance. Should be treated as any noble metal calibration.
* The upper and lower range limits of any particular type of thermocouple will depend on such factors as wire size, temperature, time of exposure, and environment. Thermocouples should only be used within the ranges listed in ASTM MNL 12 Table 3.1 (Recommended Upper Temperature Limits for Protected Thermocouples) or 3.5 (Recommended Upper Temperature Limits for Protected Thermoelements), ASTM E 230 Table 6 (Suggested Upper Temperature Limits for Protected Thermocouples), ASTM E 608 Table 1 (Suggested Upper Temperature Limits for Sheathed Thermocouples).
The temperature limits given in these tables are intended only as a guide to the user and should not be taken as absolute values nor as guarantees of satisfactory life or performance. These types and sizes are sometimes used at temperatures above the given limits, but usually at the expense of stability or life or both.

 

GLOSSARY OF TERMS

Cold Junction or Reference Junction: The junction generally at the measuring device that is held at a relatively constant temperature.

Cold Junction Compensation: Measures the ambient temperature at the connection of the thermocouple wire to the measuring device. This allows for accurate computation of the temperature at the hot junction by the measuring device.

Dual Element: Two thermocouple elements housed within one thermocouple hardware assembly.

Extension Wire: Wires which connect the thermocouple itself to a reference junction (i.e. controller, receiver, recorder, etc.). Extension wire must be of the same type as the thermocouple. Special plugs and jacks made of the same alloys as the thermocouple should be used if a quick disconnect is required for the application.

Grounded Junction: The internal conductors of this thermocouple are welded directly to the surrounding sheath material, forming a completely sealed integral junction.

Ungrounded Junction: Although the internal thermocouple conductors are welded together they are electrically insulated from the external sheath material and are not connected to the sheath in any way. Ungrounded junction thermocouples are ideal for use in conductive solutions or wherever circuit isolation is required. Ungrounded junctions are required where the measuring instrumentation does not provide channel to channel isolation.

Exposed Junction: The thermocouple junction or measuring point is exposed without any protection assembly or tube. Exposed junction thermocouples due to their design, offer the user the fastest response time.

Hot Junction: The measuring junction.

Immersion Junction: The portion of the thermocouple which is subject to the temperature which is being measured.

Measuring Junction: The junction in a thermocouple which actually measures the temperature of the object. Often referred to as the Hot Junction.

Protection Tube: A tube like assembly in which the thermocouple is installed in order to protect the element from harsh environments.

RTD: Abbreviation for Resistance Temperature Detector. It is a sensor which operates on the principle that the resistance increases with an increase in temperature at the specific rate. Commonly manufactured using a platinum resistance element. More accurate and more linear than most thermocouples and generally much more costly and slower responding.

Thermocouple: A temperature sensor based on the principle that a voltage is produced with two dissimilar metals. The junction produces a voltage in proportion to the difference in temperature between the measuring junction and the reference junction.

Thermowell: A threaded or flanged closed end tube which is mounted directly to the process or vessel, designed to protect the thermocouple from the process surroundings.

The specifications and data contained on this site are believed to be accurate and reliable. However, the information should be used for general guideline purposes only. It is the responsibility of the product user to determine the suitability of Furnace Parts LLC products for a specific application. Criterion such as wire size, temperature, time of exposure and environment may affect the recommended general reference values, and Furnace Parts LLC assumes no liability for product application.