The wonderful world of the temperature sensor

What is a temperature sensor?

Simply put, a temperature sensor is a device used to measure temperature. A temperature sensor can monitor the temperature of various components such as air, liquid or solid matter such as soil, concrete and more. There are various types of temperature sensor, each varying in performance for factors such as accuracy, range, durability and much more. Temperature sensors also have different methods of measurement based on the technology used.

What are the uses of a temperature sensor?

There are many different applications and industries that require a temperature sensor. At Withnell Sensors we have supplied sensors for the purpose of monitoring fine cheese all the way through to monitoring freezers containing some of the worlds deadliest diseases. Domestically, internal temperature sensors are often installed in many appliances such as ovens, kettles, fridges and freezers, as well as heating and air conditioning units. Cars and other vehicles also often have temperature sensors to monitor oil temperature, engine temperature and more. External temperature sensors are less frequently used domestically and key industries for these include scientific and laboratory, healthcare and veterinary, pharmaceutical, cold chain/ transportation, warehouse and industrial processing and the food industry.

The reason external temperature sensors are often used for commercial purposes is because they provide added protections and safety for the products being monitored. The data can be used to ensure stock is safe as well as for compliance purposes- evidence of consistent temperature environment conditions.

What are the types of temperature sensor and how do they work?

Thermocouples

Thermocouples are the most commonly used type of temperature sensor. The reason they are so popular is because they are self-powered, do not require excitation, operate over a broad temperature range, and provide fast response times. Thermocouple sensors work by creating a junction by joining the ends of two conductors of different metals. The temperature is therefore recorded through voltage. When the junction is exposed to heat, it generates a voltage that is relative to the temperature input, allowing the sensor to provide an accurate temperature reading.

Resistance Temperature Detectors (RTDs)

Resistance Temperature Detectors (RTDs) use ohmic resistance to measure temperature. Ohmic resistance determines temperature by measuring a material's opposition to the flow of an electric current. They are connected to a circuit in a similar way to a thermistor but they have a much wider temperature range and can measure extreme temperatures.

Thermistors

Thermistor temperature sensors, like RTD’s monitor temperature through measurable electrical resistance changes. Thermistors have a sensing element which can be either glass or epoxy coated and 2 wires so they can be connected to an electric circuit. Thermistors are typically lower cost than RTD’s but provide lower accuracy.

Temperature Probes

Temperature probes are one of the most frequently used temperature sensor. Temperature probes are also extremely diverse, they can be manufactured into a variety of housing types- coming in many different shapes and sizes and for various applications. The sensing element is usually either a thermistor, thermocouple or RTD which is topped with a terminal head.

Semiconductor based ICs

A semiconductor based temperature sensor works with dual integrated circuits (ICs). They measure the temperature changes effectively through two similar diodes with temperature sensitive voltage and current characteristics.

What are the key attributes to look for in a temperature sensor?

Temperature range

The temperature range of a temperature sensor is of course extremely important for each user. It is essential to cover all potential temperatures the sensors will monitor and consider the accuracy of the temperature sensor over the range as it may differ. So the range of the temperature sensor and the expected range of the application must be assessed at purchase.

Accuracy

The application for the temperature sensor will require a certain level of accuracy. Some applications require temperature readings to multiple decimal places whereas others not as precise. And as mentioned previously, it is important to understand accuracy at various temperatures across the range because they do differ.

Stability

The temperature stability of a temperature sensor indicates the percentage of possible error in the measurement reading. Temperature stability is therefore a vital factor in measurement accuracy and must also be considered before purchasing a logger. Size and robustness – Size is mainly dependant on the application, how much room is going to be available for each sensor and are they going to get in the way? If they are in a highly used area they also need to be robust and durable. IP ratings signify the level of protection to the elements the logger has and note qualities such as waterproof and dust proof level.

Usability

Final things to consider about the temperature sensor are its characteristics for usability. How are readings going to be taken? Is there a display or is it sent to a cloud portal? How intuitive is the software and is it extensive enough for the application. Whether the logger is wireless or wired should also be considered, some applications will require wired and some benefit greatly from wireless.