Monitoring temperature is crucial in the proper operation of many industrial applications. This is why temperature sensing devices such as thermistors and thermocouples are widely used.
While both thermistors and thermocouples can efficiently measure temperature, the way they sense temperature is what sets them apart. Thermistors rely on changes in resistance, while thermocouples generate voltage from different materials. It is important to consider the advantages and disadvantages of each type since both are viable options for temperature monitoring.
Understanding the differences between thermistors and thermocouples is crucial in choosing the appropriate temperature sensor for a particular project. Temperature sensors are essential in industrial measurements because they specify the temperature of a system or target, ensuring that it operates within the required temperature range. Any deviation from the defined limits can essentially reduce the risk of damage to the system.
Choosing the right temperature sensor can be a daunting task for those who are not familiar with the available types. To help with this decision, Ametherm offers their technical expertise in selecting the most suitable temperature sensor for a project.
Difference between NTC Thermistors and Thermocouples
An NTC thermistor is a temperature-sensing device composed of sintered semiconductor material that includes various metal oxides. These materials have charge carriers that allow current to pass through the thermistor, resulting in incremental changes in resistance proportionate to changes in temperature.
NTC thermistor output is non-linear because of its exponential nature, but it can be linearized according to the application.
NTC thermistors come in various sizes and styles, including probe assemblies, glass encapsulated, surface mount, disc and chip styles, making them adaptable for use in various industries such as automotive, aerospace, medical, and HVAC.
Although many applications that use NTC thermistors focus on resistance versus temperature characteristics, they can also meet other electrical application requirements, such as Current-Time and Voltage-Current characteristics.
A thermocouple is a device composed of two wires made of dissimilar conducting metals that are electrically bonded at two points, forming the measuring (hot) junction and the reference (cold) junction. The difference in temperature between these two junctions generates a milliampere DC voltage or thermo-electric voltage, which can then be translated into temperature by the temperature reading instrument.
Due to their ability to function well in extreme temperatures, thermocouples are primarily used in industrial settings. They are widely used in the steel and iron industries to measure and control temperatures in furnaces, kilns, and boilers.
It is difficult to predict the lifespan of a thermocouple, but its stability can be evaluated by installing it and monitoring its performance to estimate its lifespan.
Four Factors to Consider when Choosing Between a thermistor and thermocouple as a Temperature Sensor
NTC thermistors and thermocouples both operate within a wide range of temperatures, making them both ideal for a wide range of applications. NTC thermistors perform well in an operating range between -50 to 250 °C while thermocouples operate within the widest temperature range from -200 °C to 1750 °C.
Applications with a long-term operation goal require stability. Temperature sensors can drift over time, depending on their materials, construction, and packaging. For example, epoxy coated NTC thermistors can experience a drift of about 0.2 °C per year, whereas, hermetically sealed NTC thermistors experience a much smaller drift of about 0.02 °C per year. On the other hand, Thermocouples experience a drift of about 1-2 °C per year, largely due to chemical changes in the sensor, such as chemical oxidation.
NTC thermistors are highly accurate through incremental changes within their operating range. Small temperature changes reflect accurately due to large changes in resistance per °C. Thermocouples have lower accuracy and require a conversion of millivolts to temperature when used for temperature control and compensation.
Both NTC thermistors and thermocouples can operate within a wide range of applications; however, NTC thermistors are commonly found in life safety applications like fire detectors and thermometers because they are accurate and stable. Thermocouples are more often used in industrial settings due to their durability and cheaper production costs.
When it comes to temperature sensing solutions, these two options stand out. While both have their strengths, NTC thermistors stand out as an excellent choice due to their impressive performance and cost-effectiveness.
(Article content originally appeared on Ametherm’s Blog)
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