NTC Thermistor Resistance to Temperature (Beta Equation)

by the beta (B-parameter) equation 1/T = 1/T0 + (1/B) ln(R/R0) in kelvin. R0 is the nominal resistance at the reference temperature T0 (almost always 10 kohm at 25 C for the HVAC-standard sensor) and B (~3435-3950 K) is the material constant, both off the datasheet. Being NEGATIVE-coefficient, resistance FALLS as temperature RISES: a 10 kohm/3950 K sensor reads 25 C at 10 kohm, 41.5 C at 5 kohm, 10.2 C at 20 kohm. The beta form is a two-point fit good to about +/-0.2-1 C near T0; a wider or tighter job uses the 3-constant Steinhart-Hart. Distinct from a platinum RTD (positive-coefficient, Callendar-Van Dusen). The datasheet R-T curve, tolerance, and self-heating govern the field accuracy.

1/T = 1/T0 + (1/B) ln(R/R0), T and T0 in kelvin (T0 = ref_temp_c + 273.15); T = 1 / (1/T0 + (1/B) ln(R/R0)); output in C and F. R0 and B come from the sensor datasheet.

NTC thermistor beta (B-parameter) resistance-temperature equation, by name; the sensor datasheet R-T curve and tolerance govern. A wider span uses the 3-constant Steinhart-Hart equation.

The beta equation is public (a two-point Arrhenius fit); R0 (e.g. 10 kohm at 25 C) and B (e.g. 3950 K) are the two datasheet numbers for the specific thermistor, and R is the field reading.

Estimate. AHJ and licensed professional govern.

Field names used by the API: resistance_ohms, r0_ohms, beta_k, ref_temp_c, temperature_c, temperature_f

• Beta (B-parameter) equation 1/T = 1/T0 + (1/B) ln(R/R0), kelvin; NTC, so R falls as T rises; R0 and B from the datasheetNTC thermistor practice
• Two-point fit accuracy ~+/-0.2-1 C near T0; a wide span or tight accuracy uses the 3-constant Steinhart-Hart equationthermistor datasheet