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RDC Control- Canadian Thermocouple Manufacturer
RDC Control- Canadian Thermocouple Manufacturer


2) What are thermocouple color codes?

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Thermocouple Introduction

Thermocouple Types

Thermocouples and Extension Wires
  United States and International Color Coding

Standard ASTM E 230 color coding (United States) is used on all insulated thermocouple wire and extension wire when type of insulation permits. In color coding, the right is reserved to include a tracer to identify the ASTM E 230 type. Thermocouple grade wire normally has a brown overall jacket. For Types B, R and S the color codes relate to the compensating cable normally used. Various national and international standard agencies have adopted color codes for the identification of thermocouple products. These generally differ from those specified in ASTM E 230. Additionally, the overall extension color code is used to identify connectors to specific thermocouple types.

Click here to download the thermocouple color codes table in PDF format.
3) What letter of calibration should I use?
 
ASTM
E-230
Letter
Thermoelement
Trade
Name
Thermoelement
Alloys
Thermocouple Wire Protection or Insulation Material
When protected or isolated with ceramic beads or insulation material. When protected by compacted mineral insulation and outer metal sheath (MGO).
T Copper (+) Pure Copper Type T can be used in either oxidizing or reducing atmospheres, though for longer life, a protecting tube is recommended. Because of its stability at lower temperatures, this is a superior thermocouple for a wide variety of applications in low and cryogenic temperatures. It's recommended operating range is -200° to 350°C (-330° to 660°F), but it can be used to -269°C (-452°F) (boiling helium). Type T is usable from 0 to 350°C (32 to 660°F) and very stable in cryogenic and low temperature applications. For applications below 0°C (32°F) special alloy selections may be required.
Constantan (-) 45% Nickel - 55% Copper
E Chromel (+) 90% Nickel - 10% Chromium The Type E thermocouple is suitable for use at temperatures up to 900°C (1650°F) in a vacuum, inert, mildly oxidizing or reducing atmosphere. At cryogenic temperatures, the thermocouple is not subject to corrosion. This thermocouple has the highest EMF output per degree of all the commonly used thermocouples. Type E is usable from 0 to 900°C (32 to 1650°F). If the application temperature is between 600 to 1100°F, we recommend Type J or N because of short range ordering which can cause drift of +1 to +3°F in a few hours time. For applications below 0°C (32°F), special alloy selections may be required.
Constantan (-) 45% Nickel - 55% Copper
J Iron (+) Iron The Type J may be used, exposed or unexposed, where there is a deficiency of free oxygen. For cleanliness and longer life, a protecting tube is recommended. Since JP (iron) wire will oxidize rapidly at temperatures over 540°C (1000°F), it is recommended that larger gauge wires be used to compensate. Maximum recommended operating temperature is 760°C (1400°F). Type J is usable from 0 to 815°C (32 to 1500°F). Type J is not susceptible to short range ordering in the 0 to 538°C (700 to 1000°F) temperature range, (+2 to +4°F drift) which occurs with ASTM Type E and K. This low cost, stable thermocouple calibration is primarily used with 96 % pure MgO insulation and stainless steel sheath.
Constantan (-) 45% Nickel - 55% Copper
K Chromel (+) 90% Nickel - 10% Chromium Due to its reliability and accuracy, Type K is used extensively at temperatures up to 1260°C (2300°F). It's good practice to protect this type of thermocouple with a suitable metal or ceramic protecting tube, especially in reducing atmospheres. In oxidizing atmospheres, such as electric furnaces, tube protection is not always necessary when other conditions are suitable; however, it is recommended for cleanliness and general mechanical protection. Type K will generally outlast Type J because the JP (iron) wire rapidly oxidizes, especially at higher temperatures. Type K is usable from -35 to 1260°C (-32 to 2300°F). If the application is between 600 to1100°F, we recommend Type J or N because of short range ordering that can cause drift of +2 to +4°F in a few hours time. Type K is relatively stable to radiation transmission in nuclear environments. For applications below 0°C (32°F), special alloy selections are usually required.
Alumel (-) 95% Nickel - 2% Aluminum - 2% Manganese - 1% Silicon
N Nicrosil (+) 14% chromium -1.4% silicon - 84.6% nickel The type N thermocouple is used primarily at high temperatures up to 1260°C (2300°F). While not a direct replacement for Type K, Type N provides better resistance to oxidation at high temperatures and longer life in applications where sulfur is present. It also outperforms Type K in K's aging range. Type N is usable from 0 to 1260°C (32 to 2300°F). Type N overcomes several problems inherent in Type K. Short range ordering, (+2 to +4°F drift), in the 315 to 590°C (600 to 1100°F) range is greatly reduced, and drift rate at high temperatures is considerably less. Type N is also more stable than Type K in nuclear environments.
Nisil (-) 4.4% Silicon - 95.6% Nickel
R Pt 13% Rh (+) 87% Platinum - 13% Rhodium Maximum recommended operating temperature for Type S or R is 1450°C (2640°F); Type B is recommended for use at as high as 1700°C (3100°F). These thermocouples are easily contaminated. Reducing atmospheres are particularly damaging to the calibration. Noble metal thermocouples should always be protected with a gas-tight ceramic tube (Alumina) and a metal outer tube as conditions require. Only available on special request.
Pt (-) Pure Platinum
S Pt 10% Rh (+) 90% Platinum - 10% Rhodium
Pt (-) Pure Platinum
B Pt 30% Rh (+) 70% Platinum - 30% Rhodium
Pt 6% Rh (-) 94% Platinum - 6% Rhodium
C W 5% Rh (+) 95% Tungsten - 5% Rhenium This refractory metal thermocouple may be used at temperatures up to 2315°C (4200°F). Because it has no resistance to oxidation, its use is restricted to vacuum, hydrogen or inert atmospheres. Only available on special request.
W 26% Rh (-) 74% Tungsten - 26% Rhenium

1) What do thermocouple letter designations mean?

2) What are thermocouple color codes?

3) What letter of calibration should I use?

4) What is the initial accuracy of temperature sensors?

5) Is there a maximum length for thermocouples and thermocouple wiring?

6) What sheath material is the best for my application?

7) What are the maximum temperatures of thermocouples?

8) What type of junction should I use?

9) What is the response time of mineral insulated thermocouples?

10) Where should my sensor be placed?

11) What should the thermocouple resistance measure?

12) The sensor appears to be reading incorrectly. What might be wrong?

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