NTC sensors - Fast and reliable temperature measurement

02/10/2021 Know-How

Wherever precise temperature monitoring is needed, NTC (negative temperature coefficient) sensors or thermistors are the ideal choice with their diversity of standard versions and their customization opportunities.

The technology of NTC thermistors means that they offer the highest sensitivity to temperature changes. They detect changes of -3% to -5% per degree Celsius, while other resistive technologies such as platinum or nickel-based temperature sensors achieve less than just 1% per degree Celsius. NTC thermistors also offer a broad range of resistance values, which produces low voltages, allowing point-to-point measurements with maximum precision.

These properties make NTC thermistors the ideal surface temperature sensor solution for many electronic devices, for instance in power electronics, cooling system control, consumer electronics as well as numerous other industrial and automotive applications. The thermal reliability and precision in particular play an essential role in determining the lifetime of batteries and inverters.

Resistant to mechanical stress

There is an increasing number of applications that involve exposure to heavy vibrations and that need to control high power levels and high voltages in very limited space. Robust NTC sensors with specified electrical and mechanical performance values are required here, which is why Vishay has developed a large selection of NTC lug thermistors.

The lug enables the thermistors to be easily attached to the metal surface of the system using a screw. They are usually fitted directly on heatsinks, battery poles, high-voltage rails, high-current plug connectors or housings. The NTCALUGx standard family portfolio includes M2 to M6 lug terminals, and larger versions are available as customized solutions.

The NTC chip itself is located within the lug sleeve, with appropriate heat-conducting and electrically isolating safety mechanisms in place. With insulated wires, NTC thermistors offer a good thermal connection and can durably withstand operating temperatures of up to 150°C.

The electrical properties of the lug and terminals are critical in final assembly. To satisfy specific design requirements, there is a very large selection of standard sizes and customization options. For example, a nickel conductor in a closed lug ring with a small profile reduces the thermal gradient of the final assembly, which can be important, especially for temperature measurements of heatsinks.

The need to detect temperatures on elements that conduct high voltages and currents requires a higher insulation voltage between the sensor surface or the lug and the NTC's terminals. The NTCALUG series from Vishay, for example, offers insulation voltages of up to 5kV AC, providing it with a key advantage, especially in applications relating to electric vehicles such as on-board chargers (OBCs), DC-DC inverters, charger plugs and sockets, charging situations, clutch and electric traction motors, batteries and battery management systems (BMS), temperature control of MOSFETs and DC link capacitors.

These applications usually require superior mechanical strength, which can be achieved by means of larger lugs and thicker wire sections (NTCALUG01x) when establishing connections to automotive connectors. The NTCALUG03x mini-lug version offers superior reaction times and a lower temperature gradient due to the minimization of the mechanical parameters, making it perfect for modules with limited space, for example in LED lighting. The effects of mechanical stress, caused by limitations of circuit design and cable management needs, can be mitigated using right-angled lugs and flexible multicore wires.

The NTC is selected not only based on the electrical criteria but also based on a choice of screw sizes and wire thicknesses. It is also possible to make adjustments to cable lengths, to have cable insulation stripped for soldering, to have reinforced cable insulation (such as heat-shrink or silicone tubing), to include cable harnesses and to integrate any number of plug connectors for easier end device production or to connect control boards.

Rutronik's broad selection of standard and customizable LUG NTC sensor products offer a wide range of opportunities for temperature reading as well as excellent value for money. These modules with many material options are highly flexible for developers when it comes to integrating them into device designs and optimizing production efficiency. They also provide very reliable performance. Vishay's products are available with AEC-Q200 qualification, UL certification and as Pb-free/RoHS-compliant versions (without exception).


Find components at www.rutronik24.com.

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