W A T L O W Application Guide
The Art of TemperatureSensing
Tolerances on Initial Values of EMF vs. Temperature – Ref. 24
Reference Junction 0°C (32°F)
h Tolerances in the table apply to new and essentially homogeneousthermocouple compensating extension wire when used at temperatures within
the range given above.
f g i Tolerances in the table represent the maximum error contribution allowable fromnew and essentially homogeneous thermocouple extension wire when exposed
to the full temperature range given above. Extension grade materials are not
intended for use outside the temperature range shown. Thermocouple extension wire makes a contribution to the total thermoelectricsignal that is dependent upon the temperature difference between the extreme
ends of the extension wire length. The actual magnitude of any error introduced
into a measuring circuit by homogeneous and correctly connected extension
wires is equal to the algebraic difference of the deviations at its two end
temperatures, as determined for that extension wire pair. Thermocouple compensating extension wire makes a contribution to the totalthermoelectric signal that is dependent upon the temperature differencebetween the extreme ends of the compensating extension wire length.
Tolerances(whichever is greater)CalibrationTemperature RangeStandardSpecialType
Continued
°C(°F)°C(°F)°C(°F) Thermocouples
a c j Special compensating extension wires are not necessary with Type B over thelimited temperature range 0 to 50°C (32 to 125°F), where the use of non-
compensated (copper/copper) conductors introduces no significant error. For a
somewhat larger temperature gradient of 0 to 100°C (32 to 210°F) across the
extension portion of the circuit, the use of non-compensated (copper/copper)
extension wires may result in small errors, the magnitude of which will not
exceed the tolerance values given in the table above for measurements above
1000°C (1800°F). Proprietary alloy compensating extension wire is available for
use over 0 to 200°C (32 to 400°F) temperature range.**Special tolerance grade compensating extension wires are not available.
Industry specification have established theaccuracy limits of industrial thermocouples.These limits define initial sensor performanceat time of manufacture.Time, temperature andenvironment operating conditions may causesensors to change during use. Also, keep inmind that overall system accuracy will dependon the instrument and other installationparameters. B870 to 1700(1600 to 3100)±0.5%
b ±0.25%
b E0 to 870(32 to 1600)±1.7 or ±0.5%
b ±1.0 or ±0.4%
b J0 to 760(32 to 1400)±2.2 or ±0.75%
b ±1.1 or ±0.4%
b K or N0 to 1260(32 to 2300)±2.2 or ±0.75%
b ±1.1 or ±0.4%
b R or S0 to 1480(32 to 2700)±1.5 or ±0.25%
b ±0.6 or ±0.1%
b T0 to 370(32 to 700)±1.0 or ±0.75%
b ±0.5 or ±0.4%
b E
d -200 to 0(-328 to 32)±1.7 or ±1%
beb K
d -200 to 0(-328 to 32)±2.2 or ±2%
beb T
d -200 to 0(-328 to 32)±1.0 or ±1.5%
beb Temperature sensors Extension Wires
f g EX0 to 200(32 to 400)±1.7(±3.0)±1.0(±1.8)JX0 to 200(32 to 400)±2.2(±4.0)±1.1(±2.0)KX or NX0 to 200(32 to 400)±2.2(±4.0)±1.1(±2.0)TX0 to 100(32 to 200)±1.0(±1.8)±0.5(±0.9) Compensating Extension Wires
h i BX
j 0 to 200(32 to 400)±4.2(±7.6)**CX0 to 260(32 to 500)±6.8(±12.2)**RX, SX0 to 200(32 to 400)±5.0(±9.0)**
a Tolerances in this table apply to new essentially homogeneous thermocouplewire, normally in the size range 0.25 to 3 mm (0.010 to 0.118 in.) in diameter (No. 30 to No. 8 AWG) and used at temperatures not exceeding the
recommended limits on page 20 in Watlow’s Temperature Sensing SolutionsCatalog. If used at higher temperatures these tolerances may not apply. in-situ with new or known good ones to ascertaintheir suitability for further service under the conditions of the comparison. used thermocouples is likely to yieldirrelevant results, and is not recommended. However, it may be appropriate to
compare used thermocouples and donot allow for changes in characteristics with use . The magnitude of suchchanges will depend on such factors as wire size, temperature, time of exposure
and environment. It should be further noted that due to possible changes in
homogeneity, attempting to recalibrate d b c Thermocouples and thermocouple materials are normally supplied to meet thetolerances specified in the table for temperatures above 0°C. The same
materials, however, may not fall within the tolerances given for temperatures
below °C in the second section of the table. If materials are required to meet thetolerances stated for temperatures below 0°C the purchase order must so state.Selection of materials usually will be required. At a given temperature that is expressed in °C, the tolerance expressed in °F is1.8 times larger than the tolerance expressed in °C. Note: Wherever applicable,
percentage-based tolerances must be computed from temperatures that are
expressed in °C. Caution : Users should be aware that certain characteristics of thermocouplematerials, including the EMF vs. temperature relationship may change with time
in use; consequently, test results and performance obtained at time of
manufacture may not necessarily apply throughout an extended period of use.
Tolerances given above apply only to new wire as delivered to the user Type E : -200 to 0°C ±1.0°C or ±0.5 percent (whichever is greater); Type T: -200 to 0°C ±0.5 or±0.8 percent (whichever is greater).Initial values of tolerance for Type J thermocouples at temperatures below 0°Cand special tolerances for Type K thermocouples below 0°C are not given due
to the characteristics of the materials. e Special tolerances for temperatures below 0°C are difficult to justify due tolimited available information. However, the following values for Types E and T
thermocouples are suggested as a guide for discussion between purchaser and
supplier:
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