In this guide
What does 10K Type 3 mean?
In HVAC and building-automation sensor catalogs, labels such as “10K Type 3,” “10K-3,” and “10K Type III” identify an NTC thermistor curve used by a particular controller or sensor family. “10K” commonly indicates a nominal resistance of 10 kΩ at 25 °C, but the resistance-temperature curve must also match. The label alone does not specify a universal curve, accuracy, operating range, probe construction, or environmental rating.
Check the controller’s supported sensor table and the exact sensor datasheet together. For example, Johnson Controls publishes a table named “Invensys 10k Ω thermistor, type III,” while BAPI publishes its own “10K-3 Thermistor Output Table.” Those named tables are the references for their corresponding systems; do not assume every product sold as Type 3 has identical values.
Why curve matching matters
An NTC’s resistance decreases as temperature rises. The controller converts the measured resistance to temperature using a stored resistance-temperature (R/T) curve or an equivalent model. If the installed thermistor and selected controller curve differ, the displayed temperature can be wrong even when both devices are individually functioning normally.
Type III is not interchangeable with Type II, another vendor’s 10K-3 table, or a 10 kΩ thermistor specified only by its R25 value. Also distinguish a thermistor-only curve from an input configuration that includes a shunt resistor: the complete electrical arrangement determines the expected input table.
Reading a Type III resistance table
A resistance table pairs a temperature with the expected thermistor resistance. The following are selected values from Johnson Controls’ Invensys Type III table. They illustrate that specific curve only; use the full table for the controller and sensor being installed.
| Temperature | Resistance |
|---|---|
| -40 °C | 239,828 Ω |
| 21.1 °C | 11,717.32 Ω |
| 26.7 °C | 9,352.92 Ω |
| 93.3 °C | 985.06 Ω |
For a measured resistance between listed points, follow the controller manufacturer’s interpolation method. Do not treat a generic Beta value or a different manufacturer’s table as a substitute unless the controller’s documentation confirms equivalence. For the calculation basics, see our NTC resistance and temperature equation guide.
HVAC/BMS selection checklist
Before ordering or commissioning a 10K Type 3 sensor, confirm these details against the intended controller:
- Controller make/model and the exact input curve name or table revision
- Whether the input expects a thermistor directly or a shunt-resistor configuration
- Nominal resistance and reference temperature, plus the full R/T table or specified model
- Interchangeability tolerance over the required temperature interval
- Probe style, dimensions, mounting, lead/cable, connector, and thermal contact
- Actual environment, required operating interval, response needs, and applicable qualification tests
Do not infer an accuracy class, response time, service life, moisture rating, or temperature limit from “10K Type 3.” These are model-specific assembly and test specifications. Verify them in the selected product’s datasheet.
Requesting a compatible sensor
For an OEM or replacement inquiry, provide the controller model, supported curve table, target resistance and tolerance, probe dimensions, installation conditions, cable details, and test requirements. Browse NTC thermistor products or request a compatible OEM temperature sensor.
Technical references: Johnson Controls: Invensys 10k Ω thermistor, Type III table; BAPI: 10K-3 thermistor output table.
