How to Select the Right Temperature Sensor for Industrial Equipment

Types of Temperature Sensors and Key Selection Factors

Industrial equipment commonly uses four types of temperature sensors: thermocouples, RTDs, thermistors, and silicon temperature sensor ICs. Each sensor technology is designed for different operating conditions, so the selection should depend on temperature range, accuracy, response time, and system design requirements. What should be taken into consideration whileselecting includes temperature range, accuracy requirement, response time, and system requirements.

Thermocouples

Thermocouples are widely used in high-temperature environments because of their wide temperature range. For example, type K thermocouples can measure temperatures from -200°C to +1250°C. Type T thermocouples typically cover a temperature range from -200°C to +350°C.

However, it should be noticed that Thermocouples do not directly generate an absolute temperature value. They measure the voltage difference between the sensing junction and reference junction, so cold junction compensation is required. What they truly measure is the temperature difference between the sensing junction and the reference junction. This method requires cold junction compensation, making the system complex.

RTDs

Resistance temperature detectors (RTDs), such as PT100, measure temperature through the resistance change of platinum. Compared with thermocouples, RTDs provide higher accuracy and better long-term stability due to their predictable resistance-temperature relationship. High-grade PT100 RTDs can achieve around ±0.1°C accuracy under controlled measurement conditions. and typically supports a temperature range from around -200°C to +600°C.

Because of this advantage, RTDs are commonly used for motor winding monitoring, industrial power supplies, and process control systems where high measurement accuracy is required.

Although RTDs offer advantages such as wide temperature range and high accuracy, they also have several limitations, including higher costs, larger size and the need for an excitation current source. Additionally, designers also have to consider self-heating errors caused by the measurement current.

Thermistors

NTC thermistors are widely used in electronic equipment for their low cost and high sensitivity. A small temperature change can lead to a significant resistance variation, making them suitable for monitoring batteries andpower supplies. A typical NTC thermistor operates from approximately -40°C to +125°C, which is sufficient for many electronic temperature monitoring applications.

The main limitation is the complex nonlinear resistance-temperature relationship, whichdecides that the resistance can't be converted to temperature directly. A lookup table or software compensation is usually needed in converting resistance into temperature. Another disadvantage is that thermistors' accuracy is affected by aging, which may cause accuracy drift over long-term operation.

For applications requiring simple over-temperature detection or narrow temperature monitoring, NTC thermistors are an effective solution.

Silicon Temperature Sensor ICs

For PCB temperature monitoring, silicon temperature sensor ICs are usually the bestsolution. They can provide digital or analog temperature outputs without additional signal conditioning circuits. Examples include:

The ADT7310 from Analog Devices provides ±0.5°C accuracy, a 16-bit digital output, and operates from -40°C to +125°C.

The TMP117 from Texas Instruments offers ±0.1°C typical accuracy with an I2C interface, making it suitable for precision temperature monitoring in industrial and embedded systems.

The limitation of silicon temperature sensors is that most of them are not suitable for extreme-temperature environments.

How to Choose

A simple selection guideline is shown below:

Above 300°C:

Thermocouples are usually preferred.

High accuracy with wide temperature range:

RTDs are a common choice.

Cost-sensitive applications below 125°C:

NTC thermistors are suitable.

PCB-level temperature monitoring:

Silicon temperature sensor ICs provide easier integration.

These sensors are not always used individually. Usually, many industrial systems use multiple sensor types together to achieve complete temperature monitoring. For example, RTDs can monitor motor winding temperature, NTC thermistors can manage heat sink temperature, and digital temperature ICs can monitor PCB and ambient conditions. Each sensor serves a different purpose, together forming a complete temperature monitoring system.

Examples of Silicon Temperature Sensor ICs

Several temperature sensor ICs are commonly used in industrial and embedded applications: