When to Use NTC Thermistor Probes and Why It’s Necessary

NTC Thermistor Probes for green energy and automotive applications

NTC thermistor probes have long been employed to measure liquid levels and temperature in industries that extend from automotive electronics to medical technology to green energy. Their applications are endless, and their purpose is significant.

A thermistor probe is otherwise identified as a bead thermistor manufactured as a bare bead encapsulated with epoxy or glass that is usually potted in a metal or plastic housing with two high temperature insulated wires.

These NTC thermistors can be found in all the places that we live and work, from the moment we wake up and make coffee until the end of the day when we arrive home and relax in front of the television. They are indispensable to the cars we drive to work, the computers necessary to do our jobs, and the appliances we use to prepare food at the end of the day.

Understanding the impact of temperature sensing probes

Because of their prevalence, it is important to understand how NTC thermistor probes operate, in what capacity, and what their potential is. Part of this understanding includes taking into account the electrical properties of probes that abide by certain operating principles, including electrical resistance, capacitance, ultrasonics, radioactivity, and pressure and thermal conductance.

Given their pervasiveness and range of applications, and despite the large amount of thermistor sizes and shapes, it is impossible to manufacture a universal NTC thermistor probe assembly. The type of temperature sensing device used in automobiles to measure coolant temperature is vastly different from the type of temperature sensor used to measure temperature for wind turbines.

Thermistor probes in automotive innovation

Without thermistor temperature sensing probes many automobiles, appliances, industrial equipment, and anything that requires electricity essentially would not function properly, or at all. Engineers depend on these NTC thermistor sensors as a design consideration for any product that generates energy, hot or cold, and requires temperature measurement, control, and accuracy.

In 1966, automotive vehicles used around two thermistors per unit to report to various gauges and electronic control modules. In the 1970s that number grew to 15, in the 1980s to 40 NTC sensors, and in the 90s there were 60 thermistor temperature sensors in vehicles. Today, automotive vehicles use between 80 to 100 NTC thermistors.

This exponential increase in temperature sensing devices has mainly been fueled over time by the complexity and refinement of technology in automotive vehicles. As automotive technology has increased and improved, so has the demand for temperature sensors. The need to detect, regulate, and control temperature in vehicles can be seen in car seat heaters and air conditioners, oil temperature gauges, defrosters for windows and mirrors, li-ion batteries in electric vehicles, and even just the heating and cooling systems that regulate and control cabin temperature of vehicles.

Additionally, more features and processes require sensing to improve vehicle performance, driver convenience, automotive safety, and reduce or control emissions. Vehicles today exhibit more artificial intelligence, part of which is the need to sense and regulate temperature. As an example, thermostats that in the past were used to measure coolant temperature and control cabin climate temperature now have been replaced with a thermistor temperature sensor, which has a faster response time as well as being more accurate. Another indispensable application of NTC sensors in automobiles is the ability to detect oil levels and viscosity and then alert the driver or operator when to change it.

Green energy, medical technology and other applications for NTC probes

In the medical field thermistor temperature sensing probes are critical because of their high sensitivity, high accuracy, and interchangeability. A good example is a respirator. Air entering a patient’s lungs must be exactly 37 °C, the same as body temperature. A temperature sensing device analyzes the air temperature and sends a signal to the respirator to regulate and compensate as needed.

In our homes, NTC thermistor sensors are everywhere in microwave ovens, toasters, dishwashers, air conditioning units, portable heaters, washers and dryers, bidets, hot tubs, saunas, refrigerators, electric kettles, to name a few. Without a temperature sensor to determine heat, a microwave oven is prone to overheating. Same with portable heaters, which also use sensors, could possibly get too hot and start a fire.
NTC Thermistor probes are used in wind turbines and solar panels

Green energy is an area where the use of temperature sensing probes is making great strides. Wind turbines are a great example where the use of NTC probes is essential. Wind turbines in colder countries or environments are prone to freezing. A thermistor probe used on the fan blade with two very long leads regulates and senses the air temperature to control the on/off actions of the wind turbine’s heater so that the blades won’t freeze. If the blades freeze, this creates inefficiencies and makes the entire unit inoperable.

How to select and integrate thermistor probe assemblies into different applications

Similar to the limitless applications requiring NTC thermistor probe assemblies, so too exist the endless methods to mount them, adhere them, and apply them. Some probe assemblies can get very sophisticated in the ways that they are housed and the methods in which they are mounted.

When talking about a probe, this actually is referring to the metal or plastic assembly housing that covers the bead thermistor for different applications and functions. These probes come in all shapes, sizes, and mounting options. Some NTC thermistor probes are long and narrow with a stainless steel housing used in vehicles for measuring oil or water temperature. Other temperature sensing probes integrate a threaded tube that are used in engines or medical equipment to detect and monitor temperature. Probes with a design that features a ring lug are often used together with heatsinks or lithium-ion batteries.

Each thermistor temperature sensing probe starts out as a chip that is then encapsulated in either glass or epoxy. Depending on the application, this bead thermistor is then potted in a metal or plastic housing that is customized according to very specific requirements.

When used with an application such as a lithium-ion battery, am NTC probe with a ring lug can be easily mounted securely to the battery terminal. This probe assembly can then effectively monitor the battery temperature so it does not rise above a certain degree.

In the chart below, we illustrate different thermistors and the housing with which they are compatible.

 

 
ProbePANRPANTPANWPANEPANHPANG
Thermal Time Constant (S)40402510103
Dissipation Constant (mW/°C)3310333
Max Power (mW)125125125125125125
Type of HousingTinned Metal Ring LugStainless Steel 304 Threaded Tip & HexAluminum Threaded Metal Tubing & HexProbe Assembly with EpoxyStainless Steel 304 Closed End Metal TubingGlass Bead
Description of ProbeEpoxy dip coated NTC thermistor potted in tinned copper ring lugNTC thermistor potted inside aluminum hex screw with straight threadsNTC thermistor potted at the tip of durable stainless steel allow tube with tapered thread hex screwEpoxy dip coated NTC thermistor soldered between jacketed Teflon/PVC wiresNTC thermistor inside durable stainless steel alloy tube and epoxy filledGlass encapsulated bead thermistor with Teflon coated wires

 

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