NTC Thermistors, Temperature Probes and Inrush Limiters
NTC thermistors: sensing and power-on surge control
NTC means negative temperature coefficient: electrical resistance decreases as the sensing element gets warmer. The NTC products here serve two distinct functions. High-resistance sensing elements and wired probes feed temperature-measurement circuits; low-resistance power NTC disks such as MF72 and 5D/10D series limit inrush current while they warm. Matching the letters “NTC” or a resistance number is not enough to exchange these devices.
Temperature sensing choices
- Unwired elements: epoxy-coated MF52/MF52B and related beads, thin-film MF5B-style elements, and 0201/0603 SMD variants offer selected nominal resistance, B coefficient, tolerance, case and lead dimensions. The 25°C resistance (R25), for example 10 kΩ or 100 kΩ, is just one point on the resistance–temperature curve. B3380, B3435, B3950 and B4250 choices cannot be assumed equivalent at other temperatures.
- Ready-to-mount probes: stainless-look cylindrical, air, surface-contact, threaded M4/M6/M8, magnetic and sheathed probe listings offer differing head sizes, cables, connectors and lengths. Match thermal placement, response time, connector wiring and the whole assembly's actual temperature and ingress limits. “Waterproof” in a listing does not prove immersion suitability of a cable joint or plug.
- Reader and controller boards: some options are RS485/Modbus or TTL/RS232 temperature-acquisition modules or thermostat/fan-control boards, not standalone sensing resistors. One seven-channel reader lists 10 kΩ B3950 sensors and offers a board-only option versus sensor bundles; inspect the selected contents and module supply range before purchase.
Inrush limiting choices
MF72 and related disk options labeled 1.5D, 5D, 10D, 20D and similar values use low cold resistance and a diameter/series designation, not the 10 kΩ R25 and B-value scheme of a temperature probe. In a power input these devices heat under load, reducing resistance after startup. Select the exact part using its published cold resistance and tolerance, steady-state RMS current, energy and surge ratings, hot resistance, expected repeated-start interval and ambient temperature. A hot device can offer less surge limitation if power is reapplied before it cools. This component is not a fuse, isolation device or substitute for a correctly designed protective circuit.
Selection checklist
- First determine whether your circuit measures temperature or controls input inrush.
- For measurement match R25, B constant or full R–T table, accuracy across the required range, readout calibration and self-heating. Specify the probe head, cable length and connector separately.
- For inrush match the circuit voltage/current and the particular disk's documented electrical and thermal ratings, not just its diameter or cold ohms.
- Check the exact variant and quantity. Some assortments contain multiple D-series disks, while a probe listing can vary between 5K, 10K, 50K and 100K or between B3435 and B3950.
Related but different products
A few results mention PTC components, PT100/PT1000 platinum RTDs or DS18B20 digital sensors. PTC resistance behavior is different; an RTD has a different measurement characteristic and a DS18B20 sends digital data. None becomes a compatible NTC merely because the probe body, cable or application looks similar. For appliance and mains-connected replacements, confirm the equipment service specification and selected component's documented ratings; do not rely on “original” or appliance-fit claims without evidence.
FAQ
Does 10K B3950 equal 10K B3435? No. Both may read 10 kΩ at 25°C but their temperature curves differ. The controller must support the selected curve.
Can a 10D-11 disk measure temperature for a 10K controller? No. It is a low-resistance, self-heating inrush limiter intended for a power circuit, not a calibrated 10 kΩ sensing element.
Does the RS485 module include probes? Not for every option. A board-only variant can require separately selected 10 kΩ B3950 probes; check the exact bundle.
