Reference Data on Thermocouple & Platinum Resistance Thermometry

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Reference Data on Thermocouple & Platinum Resistance Thermometry

REFERENCE DATA ON THERMOCOUPLE THERMOMETRY

Thermocouple Accuracies
Base Metal Extension and Compensating Wires and Cable Types and Tolerances
Table of Thermocouple Wire Tolerances
Wire and Cable Data
Conductor Size Equivalents (diameter)
Conductor Cross Sectional Areas
Insulated Wire Sizes (Subject to variation)
Loop Resistance, Ohms per Combined Metre Approximate

REFERENCE DATA ON PLATINUM RESISTANCE THERMOMETRY

Tolerances for Pt100 Thermometers to IEC 751: 1983
Connection Configurations and Termination Colour Codes

REFERENCE DATA ON THERMOCOUPLE THERMOMETRY

Thermocouple Accuracies

Tolerance classes for thermocouples to IEC 584-2: 1982.

Note: t = actual temperature

Use the larger of the two deviation values.

Base Metal Extension and Compensating Wires and Cable Types and Tolerances

Thermocouple Wire Types and Codes IEC 584-3: 1989

*Magnetic ( ) Alternative & Trade Names

Identification as to whether a thermocouple cable type is extension or compensating is indicated in the example which follows; however, please note that a letter A or B after the C for Compensating refers to the Cable Temperature Range in accordance with the Table of Tolerance Values set out in this standard.

K X 1 = K EXTENSION CLASS 1

K CA 2 = K COMPENSATING CLASS 2 0 to 150°

Table of Thermocouple Wire Tolerances

The figures shown in the tables are those appropriate to the measuring junction temperatures in the final column. In most cases the error expressed in degrees Celsius will be larger at lower thermocouple junction temperatures.

Notes:

Cable temperature range may be restricted to figures lower than those shown in the table because of temperature limitations imposed by the insulant.
A cable comprising two copper conductors may be used with type B thermocouples. The expected maximum additional deviation within the cable temperature range 0°C to +100°C is 40µV. The equivalent in temperature is 3.5°C when the measuring junction of the thermocouple is at 1400°C.

Wire and Cable Data

Thermocouple Wire

Twin, single conductor, having a temperature / e.m.f. relationship to the appropriate standard over the complete temperature range.

Extension Cable

Twin, stranded conductors for connection between measuring thermocouple and instrument (or external reference junction) of the same materials as the thermocouple and having the same e.m.f. / temperature characteristics over a temperature range limited by the insulation material.

Compensating Wire or Cable

Twin, single or standard conductors for connection between measuring thermocouple and instrument (or external reference junction) of different composition from the thermocouple material, but having similar e.m.f / temperature characteristics over a limited temperature range. Types U and Vx in Conductors Table.

Connection of Thermocouples to Measuring Instruments

Ordinary copper wires should never be used, as the error will be equal to the difference in temperature between the connecting point of the thermocouple and the instrument (or external reference junction).

Extension or compensating wire or cable must be employed, and it is essential that the same polarity is maintained. If the polarity is reversed, the error is equal to twice the temperature difference between the connecting point of the thermocouple and the instrument (or external reference junction). For maximum accuracy extension cables should be used, and the terminals and connectors should be of thermocouple materials to maintain continuity.

Single / Multi-strand

The choice is mainly determined by the application (e.g. termination considerations and internal diameter of associated sheath). Generally, single strand wires are used for hot junctions, and multistrand for extensions of the thermocouple as being more flexible. The greater the effective conductor diameter, the lower the value of thermocouple loop resistance; an important consideration with long cable runs.

Conductor Size Equivalents (diameter)