When designing a temperature sensing circuit, the most important thing is not to exceed the actual amount of power required. By understanding the requirements of your application, you can choose the best temperature sensor to minimize cost without compromising performance, accuracy or reliability. There are several factors to consider when choosing a sensor.
Temperature sensor selection
| NTC | RTD | Thermocouple | |
| Measurement range | -50℃~250℃ | -200℃~600℃ | -200℃~1750℃ |
| Cost | Lower cost | Higher cost | Medium cost |
Temperature range selection
The primary consideration when choosing a temperature sensor is the temperature range. For example, thermocouples are often the only choice for operating environments above 1000 °C. However, only a few applications involve this extreme temperature.
For most industrial, medical, automotive, consumer and general purpose embedded systems, the typical operating temperature range is much narrower.
Probe
Temperature sensing components require different packaging, depending on the application structure being measured.
Low cost sensors are available in epoxy coated packages. For higher temperature operation, the temperature sensor can be sealed in the glass. This protects the temperature probe from other environmental factors, including liquids and debris. The sensor can also be placed in a stainless steel housing for added stability. The higher the complexity required for the enclosure, the higher the cost of the sensor.
The sensors are also available in a variety of shapes and sizes. Choosing the right sensor for your application can improve performance, responsiveness and reliability. For example, all temperature sensors are subject to self-heating due to their power. This self-heating increases the ambient temperature around the sensor, introducing errors and negatively impacting accuracy.
Using an NTC thermistor, the quality of the sensor can be increased to reduce errors due to self-heating. Even small size changes can have a major impact on reducing self-heating. For example, a 3 x 3 x 3 mm thermistor has a volume/mass greater than 3 times compared to a 2 x 2 x 2 mm thermistor. Only a thermistor can achieve this flexibility. Semiconductor based sensors are inherently fixed. Since RTDs and thermocouples are wire-based, this limits the ability of engineers to adjust quality to reduce self-heating errors.