BMS Temperature Sensors

The specification of a 10K3A1 temperature sensor

A 10K3A1 temperature sensor is a 10 kΩ NTC thermistor commonly used in HVAC/BMS applications. The designation generally refers to the 10K Type 3 / 3A1 thermistor curve.

Specification	10K3A1
Sensor type	NTC thermistor
Nominal resistance	10,000 Ω at 25°C (77°F)
Resistance characteristic	Resistance decreases as temperature increases
Nominal Beta (β) value	≈ 3976 K
Common designation	10K Type 3 / 10K3A1
Reference temperature	25°C
Typical operating range	Approximately −40°C to +125°C, depending on sensor construction
Typical accuracy	Usually ±0.2°C to ±0.5°C around normal HVAC temperatures, depending on the manufacturer
BMS input	Passive resistive / thermistor input
Polarity	None

Typical 10K3A1 resistance values

Approximate values useful for BMS commissioning and fault finding are:

Temperature	Approx. Resistance
−20°C	96.8 kΩ
−10°C	55.3 kΩ
0°C	32.6 kΩ
5°C	25.4 kΩ
10°C	19.9 kΩ
15°C	15.7 kΩ
20°C	12.5 kΩ
25°C	10.0 kΩ
30°C	8.06 kΩ
35°C	6.53 kΩ
40°C	5.33 kΩ
50°C	3.60 kΩ
60°C	2.49 kΩ
70°C	1.76 kΩ
80°C	1.27 kΩ
90°C	0.93 kΩ
100°C	0.70 kΩ

For Tridium Niagara N4

For an N4 controller/input configured for a 10K3A1 thermistor, the important characteristics are:

R25 = 10,000 Ω
Beta ≈ 3976 K

One important point: 10K thermistors are not interchangeable just because they all measure 10 kΩ at 25°C. A 10K Type 2, Type 3/3A1 and other 10K curves can produce significantly different temperatures away from 25°C. For a BMS specification, I would therefore specify “10 kΩ NTC, Type 3/3A1 characteristic, R25 = 10 kΩ” rather than simply “10K thermistor.”

Below is the full 10K3A1 resistance/temperature table from −40°C to +120°C in 1°C increments, calculated using:

Temp °C	Resistance Ω	Temp °C	Resistance Ω
-40	411,749	41	5,070
-39	382,827	42	4,871
-38	356,157	43	4,680
-37	331,548	44	4,498
-36	308,825	45	4,324
-35	287,832	46	4,158
-34	268,423	47	4,000
-33	250,469	48	3,848
-32	233,850	49	3,703
-31	218,457	50	3,564
-30	204,192	51	3,431
-29	190,964	52	3,304
-28	178,691	53	3,183
-27	167,297	54	3,066
-26	156,712	55	2,955
-25	146,875	56	2,848
-24	137,727	57	2,746
-23	129,215	58	2,648
-22	121,291	59	2,554
-21	113,910	60	2,463
-20	107,031	61	2,377
-19	100,617	62	2,294
-18	94,633	63	2,215
-17	89,048	64	2,138
-16	83,831	65	2,065
-15	78,958	66	1,995
-14	74,402	67	1,927
-13	70,141	68	1,862
-12	66,154	69	1,800
-11	62,421	70	1,740
-10	58,925	71	1,682
-9	55,649	72	1,627
-8	52,578	73	1,574
-7	49,698	74	1,522
-6	46,995	75	1,473
-5	44,458	76	1,426
-4	42,075	77	1,380
-3	39,836	78	1,336
-2	37,731	79	1,294
-1	35,752	80	1,253
0	33,890	81	1,214
1	32,138	82	1,176
2	30,487	83	1,140
3	28,933	84	1,105
4	27,468	85	1,071
5	26,088	86	1,038
6	24,785	87	1,007
7	23,557	88	977
8	22,397	89	947
9	21,302	90	919
10	20,268	91	892
11	19,291	92	866
12	18,367	93	840
13	17,493	94	816
14	16,667	95	792
15	15,885	96	769
16	15,145	97	747
17	14,444	98	726
18	13,780	99	705
19	13,151	100	685
20	12,554	101	666
21	11,988	102	648
22	11,452	103	630
23	10,942	104	612
24	10,459	105	595
25	10,000	106	579
26	9,564	107	563
27	9,150	108	548
28	8,756	109	533
29	8,382	110	519
30	8,026	111	505
31	7,687	112	492
32	7,365	113	479
33	7,058	114	466
34	6,765	115	454
35	6,487	116	442
36	6,222	117	431
37	5,969	118	420
38	5,728	119	409
39	5,499	120	399
40	5,279

For Niagara N4 / BMS commissioning, some useful checkpoints from this calculated curve are:

0°C = 33.89 kΩ
10°C = 20.27 kΩ
20°C = 12.55 kΩ
25°C = 10.00 kΩ
30°C = 8.03 kΩ
40°C = 5.28 kΩ
50°C = 3.56 kΩ
60°C = 2.46 kΩ
70°C = 1.74 kΩ
80°C = 1.25 kΩ
90°C = 919 Ω
100°C = 685 Ω

One caution: this is a Beta-equation calculation using β = 3976 K. A manufacturer’s official 10K3A1 thermistor curve may use Steinhart-Hart coefficients or a resistance lookup table, so small differences are possible, especially at the extremes of the temperature range.