Three elements that are not interchangeable
A room or duct temperature sensor in a building is a passive resistor, and the controller has to be told which kind. Three kinds dominate, and at 20 °C they read:
| Element | Resistance at 20 °C | Change per degree near 20 °C |
|---|---|---|
| NTC 10 kΩ, β = 3950 K | about 12 535 Ω | falls by about 4.6 % |
| Ni1000 (DIN 43760) | 1112.36 Ω | rises by about 5.8 Ω |
| PT1000 (IEC 60751) | about 1077.9 Ω | rises by about 3.9 Ω |
A PT1000 connected to an input configured for Ni1000 reads about six degrees low at 20 °C, and the error changes with temperature. The PT100 / PT1000 calculator covers both platinum and DIN nickel elements, with full tables for Ni1000 and PT1000, and the NTC calculator covers thermistors.
Two cautions about names. “Ni1000” is also used for a nickel element with a different curve (5000 ppm/K), common in some controller families; it is 1000 Ω at 0 °C as well but does not follow the DIN 43760 values, and it is not covered here. And “10 kΩ NTC” describes only the resistance at 25 °C: parts with β = 3380 K and β = 3950 K differ by about 5400 Ω at 0 °C, 28.2 kΩ against 33.6 kΩ. Take the curve from the sensor’s datasheet, not from the nominal value.
Two wires and long cables
Building sensors are wired with two conductors, so the cable resistance is added to the reading. The higher the element resistance, the less it matters: 50 m of 0.5 mm² cable adds 3.4 Ω, which is about 0.9 °C on a PT1000, about 0.6 °C on a Ni1000 and nothing visible on a 10 kΩ thermistor. On a PT100 the same cable would add about 9 °C, which is why PT100 is rare in buildings. The RTD lead-wire error calculator gives the figure for platinum elements.
Small pressures
Duct static pressure, filter loading and room pressurisation are measured in pascals or in inches of water column: 250 Pa is 1.0037 inH₂O. The pressure converter handles these along with the bar and psi of the water side.
Humidity as dew point
Condensation on a chilled ceiling, a cold pipe or a window depends on the dew point of the room air, not on its relative humidity. Air at 26 °C and 60 % relative humidity has a dew point of 17.6 °C: a chilled surface must stay above that. The dew point calculator converts between the two and gives the water content of the air.
0–10 V signals and input resolution
Active sensors in buildings mostly use 0–10 V rather than 4–20 mA. A 0–10 V signal has no live zero, so a broken wire reads as the bottom of the range and cannot be told from a real value; where that matters, 2–10 V or 4–20 mA is used. Resolution depends on the controller’s converter: a 10-bit input over 0–10 V resolves a 0 to 50 °C transmitter in steps of about 0.05 °C. The ADC resolution calculator works this out for any input.
Machines
Fans, pumps and chillers are judged by vibration velocity in mm/s. The vibration converter converts the reading of an accelerometer and shows the ISO 10816-3 zone for machines above 15 kW; smaller fans and pumps fall outside that standard.
Outside the scope of this site
Air-quality sensors for CO₂ and volatile compounds, air-flow measurement and energy metering are not covered here.
Updated October 11, 2026