Thermocouple sheath material and maximum temperatures - RDC Control

RDC Control- Canadian Thermocouple Manufacturer

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

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Thermocouple Introduction

Thermocouple Types

Thermocouples and Extension Wires

In mild corrosive environments and general purpose applications, 304 SS and 316 SS are usually the best choice when considering cost versus performance. Choose Alloy 600 over 304 SS or 316 SS when temperatures exceed 899°C (1650°F).

Mineral Insulated (MGO) Thermocouple Sheat Material Characteristics.
Sheath Material	Melting Point		Max. Temp.		Application Notes
Sheath Material	°C	°F	°C	°F	Application Notes
304SS	1400	2550	900	1650	General purpose stainless steel. Good corrosion resistance.
316SS	1370	2500	1125	1700	General purpose stainless steel. Superior corrosion resistance.
310SS	1400	2550	1150	2100	Same as 316 SS. Higher temperature rating.
446SS	1480	2700	1100	2000	Used in sulphur atmospheres
Inconel 600	1400	2550	1150	2100	Excellent oxidation and corrosion resistance at high temperature.
Pyrosil D	1420	2585	1250	2280	Superior oxidation resistance to 310SS & Alloy 600. Superior high temperature strength to 310SS & INC 600. Compatible thermal co-efficient of expansion to nickel based type K and type N thermoelement wires.

7) What are the maximum temperatures of thermocouples?

The diameter of the sensor wires determines the upper most operating temperature. The larger the diameter, the higher the temperature rating. Choose alloy 600 over 304 SS or 316 SS when higher temperatures are expected. The environment is another critical factor when determining the best material.

Mineral Insulated (MGO) Thermocouple Suggested Upper Limits per Outside Diameter
T/C Type	1/25"		1/16"		1/8" - 3/16"		1/4"		5/16"		7/16"
T/C Type	°C	°F	°C	°F	°C	°F	°C	°F	°C	°F	°C	°F
J	500	900	700	1100	700	1200	700	1200	700	1200	700	1200
T	200	300	300	400	400	700	400	700	400	700	400	700
K	800	1400	1000	1800	1200	2000	1200	2000	1200	2000	1200	2100
N	800	1400	1000	1800	1200	2000	1200	2000	1200	2000	1200	2100
E	600	1000	700	1200	700	1200	1000	1800	1000	1800	1000	1800

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?