Catalogue - Sensor catalog - Watlow - (Version JPG)

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Radiant heater, Resistance heater, Coil heater, Controller, Thermocouple

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General Information

Application Hints

What should the thermocouple resistance measure?

Ohms per Double Feet

Long lead wire runs, or the use of analog based instrumentation, make conductor resistance an important consideration in selecting the wire gauge best suited for your

application. The table below lists the nominal ohms per double feet for thermocouple and thermocouple extension wire. Ohms per double feet is the total resistance, in ohms, for both conductors, per foot.

Although resistance cannot confirm the alloy has the correct thermoelectric specifications, it will check to see if other undesirable characteristics like opens, poor welds, or corrosion of the wires are present. Always measure the resistance of the thermocouple out of the application so the EMF output is not in conflict with the resistance meter.

Nominal Resistance for Thermocouple Alloys in Ohms per Double Feet at 20°C

Calibration Type


AWG	Diameter
Gauge	in.	(mm)	BX		E	J	K	N	RX,SX	T
2	0.258	(6.543)			0.011	0.006	0.009	0.012
4	0.204	(5.189)			0.017	0.009	0.014	0.019
6	0.162	(4.115)			0.028	0.014	0.023	0.030
8	0.129	(3.264)			0.044	0.023	0.036	0.048
10	0.102	(2.588)			0.070	0.036	0.058	0.077
12	0.081	(2.053)	0.015	0.058	0.111	0.057	0.092	0.123	0.006	0.048
14	0.064	(1.630)	0.024	0.093	0.177	0.091	0.147	0.195	0.010	0.076
16	0.051	(1.290)	0.039	0.147	0.281	0.145	0.233	0.310	0.016	0.120
18	0.040	(1.020)	0.063	0.238	0.453	0.234	0.376	0.500	0.025	0.194
20	0.032	(0.813)	0.098	0.372	0.709	0.367	0.589	0.783	0.040	0.304
22	0.025	(0.645)	0.156	0.592	1.129	0.584	0.937	1.245	0.063	0.483
24	0.020	(0.508)	0.248	0.941	1.795	0.928	1.490	1.980	0.100	0.768
26	0.016	(0.406)	0.395	1.495	2.853	1.476	2.369	3.148	0.159	1.221
28	0.013	(0.320)	0.628	2.378	4.537	2.347	3.767	5.006	0.253	1.942
30	0.010	(0.254)	0.999	3.781	7.214	3.731	5.990	7.960	0.402	3.088
32	0.008	(0.203)	1.588	6.012	11.470	5.933	9.524	12.656	0.639	4.910
34	0.006	(0.152)	2.525	9.560	18.239	9.434	15.145	20.126	1.016	7.808
36	0.005	(0.127)	4.015	15.200	29.000	15.000	24.080	32.000	1.615	12.415
14 Stranded	0.076	(1.930)	0.022	0.085	0.161	0.083	0.134	0.178	0.009	0.069
16 Stranded	0.060	(1.520)	0.035	0.134	0.256	0.133	0.213	0.283	0.014	0.110
18 Stranded	0.048	(1.220)	0.056	0.214	0.408	0.211	0.338	0.450	0.023	0.174
20 Stranded	0.038	(0.965)	0.090	0.340	0.648	0.335	0.538	0.715	0.036	0.277
22 Stranded	0.030	(0.762)	0.143	0.540	1.031	0.533	0.856	1.137	0.057	0.441
24 Stranded	0.024	(0.610)	0.227	0.859	1.639	0.848	1.361	1.808	0.091	0.701

*Not an ASTM E 230 symbol

Note: BX, CX, RX and SX indicates compensating thermocouple materials.

Conductor Sizes



	oOHd		Stranded
Wire Size	Diameter		Diameter		Number	Strand
AWG Gauge	in.	(mm)	in.	(mm)	of Strands	Gauge

14	0.064	(1.630)	0.076	(1.930)	7	22
16	0.051	(1.290)	0.060	(1.520)	7	24
18	0.040	(1.020)	0.048	(1.220)	7	26
20	0.032	(0.813)	0.038	(0.965)	7	28
22	0.025	(0.635)	0.030	(0.762)	7	30
24	0.020	(0.508)	0.024	(0.610)	7	32
26	0.016	(0.406)
28	0.013	(0.330)
30	0.010	(0.254)
32	0.008	(0.203)
34	0.006	(0.152)
36	0.005	(0.127)

Sensor catalog - Watlow - #24

Radiant heater, Resistance heater, Coil heater, Controller, Thermocouple