Testing Temperature Sensors

Most solar control units use 10K (thermistor type) temperature sensors to monitor temperature differentials. The accuracy of temperature sensors can be determined with the use of an Ohm meter. Sensors can be tested by connecting both leads from the meter to both wires from the sensor. The meter will show either an open circuit, short circuit or numbers that can be matched to the chart below to determine the temperature of the sensor.

Note: Some older Delta-T solar controls used 3K sensors.

TEMPERATURE VERSUS RESISTANCE CONVERSION CHART Note: Temperature readings are in degrees Fahrenheit. Sensor readings are Ohms (x1000)

3K	ºF	10K		3K	ºF	10K
70.48	-30	234.0		1.462	108	4.873
49.63	-20	165.4		1.399	110	4.663
35.42	-10	118.1		1.339	112	4.464
25.60	0	85.35		1.282	114	4.274
18.73	10	62.44		1.228	116	4.093
13.86	20	45.19		1.176	118	3.921
10.36	30	34.54		1.127	120	3.757
9.789	32	32.63		1.080	122	3.601
9.251	34	30.84		1.036	124	3.453
8.746	36	29.15		.993	126	3.311
8.272	38	27.57		.953	128	3.176
7.827	40	26.09		.914	130	3.047
7.408	42	24.69		.877	132	2.924
7.015	44	23.38		.842	134	2.807
6.644	46	22.15		.809	136	2.695
6.296	48	20.99		.777	138	2.589
5.968	50	19.89		.746	140	2.487
5.660	52	18.78		.717	142	2.389
5.369	54	17.90		.689	144	2.296
5.095	56	16.98		.662	146	2.208
4.836	58	16.12		.637	148	2.123
4.593	60	15.31		.612	150	2.042
4.363	62	14.54		.589	152	1.964
4.146	64	13.82		.567	154	1.890
3.941	66	13.14		.546	156	1.819
3.748	68	12.49		.525	158	1.751
3.565	70	11.88		.506	160	1.686
3.392	72	11.31		.487	162	1.624
3.229	74	10.76		.469	164	1.564
3.074	76	10.25		.452	166	1.507
2.928	78	9.760		.436	168	1.452
2.790	80	9.299		.420	170	1.400
2.659	82	8.862		.405	172	1.349
2.535	84	8.449		.390	174	1.301
2.417	86	8.057		.377	176	1.255
2.306	88	7.686		.363	178	1.211
2.200	90	7.334		.351	180	1.168
2.100	92	7.000		.294	190	.980
2.005	94	6.683		.248	200	.827
1.915	96	6.383		.210	210	.700
1.829	98	6.098		.179	220	.596
1.748	100	5.827		.153	230	.510
1.671	102	5.570		.113	250	.377
1.598	104	5.326		.085	270	.284
1.528	106	5.094		.065	290	.217

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