Technology insights

Introduction to Lightweight and Compact Thermal Sensor Modules

Thermal imaging cameras are devices designed to detect infrared radiation across a range of applications. All objects radiate heat or infrared radiation that can be detected. The process of detecting radiation and processing infrared-based images from it, is called infrared thermography.
sensor arrays

The idea of thermal sensing is to be able to detect temperature gradients and process the images to indicate these hotspots. In modern engineering and industry, predictive maintenance is key. Here, hotspots are very informative as they are often early indicators of imminent component failure. For example, in high voltage power lines and even transformers, the presence of hotspots in wires or insulation components will indicate that there could be a fire. Integrated thermal sensors are also ideal for industrial processes that require temperature control, along with a monitoring system, for an instant indication of equipment issues and fire detection.
depth sensor

Infrared Detection Applications

Infrared is a universal emission for all objects. The example that everyone will identify with is the passive IR camera/sensor that can detect heat emissions. These emissions can be from a variety of sources, for example, sensors can detect hotspots in barrels and industrial waste sites at risk of fire. Other applications include detecting IR emissions from poorly insulated buildings to increase efficiency and optimize building energy saving. Smaller sensors are very useful in a process context. For example, in a factory with heating and cooling steps for its manufacturing process, monitoring heat variations and timings can prevent refractory and insulation materials to crumble and fail and machines can adapt their speed or send alerts to assembly line operators accordingly. Accurate thermal sensors are becoming increasingly important as industries embrace digital transformation. Manufacturing automation or process monitoring are the most common places where you can find thermal sensors in the industry.

What are they and How do they Work?

Passive infrared detector systems are small integrated detectors that use semiconductor systems to detect emitted radiation and pass generated signals to a data processing system. They work by detecting IR radiation emitted by objects. Infrared enters through the sensor face at the exposed leading face of the sensor. The core of the PIR sensor consists of a solid-state sensor, which is usually arranged in layers of pyroelectric material. Pyroelectric materials generate an electrical signal when they detect IR radiation and this is augmented for detection and processing. These sensors are generally around 40 mm2 and this means they are of a size where they can be integrated into space-limited areas or in arrays with other types of sensors.
thermal infrared camera

The Demands for a Good Thermal Sensor

A good thermal sensor has a number of requirements in the competitive market generated by industry 4.0 applications. In general, sensors should be small, powerful and unobtrusive. This is because there are very strict space and weight constraints for incorporating thermal sensors in new hardware products. The important factor is that the sensor should be powerful and able to cover a greater field-of-view so that neighboring sensors can integrate into a detector array and their images will overlap and cover a larger area. Continuing the integration theme, thermal sensors also need to be able to fit into larger more complex multiple sensor systems to provide a combined multi-purpose signal. By configuring the PIR sensor in a differential mode, it can also be used as a motion detector device. This means when heat is detected in the line of sight of the sensor, a signature of two or more pulses at the output of the sensor triggers an alarm indicating the detection of movement. This places the emphasis on sensor fusion and often requires clever engineering to ensure that different sensing technologies work in harmony with the same detection system.
thermal video camera

TeraRanger Evo Thermal

The TeraRanger Evo family is a range of thermographic sensors that provide excellent performance in a small and compact device. The weight of each sensor module is from 7-9 grams and they are designed to integrate into a range of applications across industry, security and the environment. The Evo Thermal sensor module comes with various fields of view depending upon how much area there is to cover. There is a 33° and 90° version. The Evo Thermal 33, which has a 32x32 resolution, provides a more detailed image than the 90 version and has a slightly longer range and a higher sampling rate (14Hz). The sensors are able to operate in a range of conditions (indoor, outdoor, darkness or bright sunlight) to detect hotspots and temperature gradients. Passive sensors such as these can easily detect human body heat signatures at a range of around 13 meters.

The TeraRanger thermal sensor is a modular system that comes in two interchangeable parts, i.e., the back thermographic module and the yellow backboard that provides the communication and power management suitable for the system. The backboard can include USB, or UART interfaces and is ready for OEM integration.

The Future

The majority of PIR sensors have a range of 10-13 meters and, with a wide field of view; it can easily be seen how a small number of detectors in an array can cover a relatively large space. This is why PIR-based systems are so practical for industrial heat and fire detection, controlling heat-sensitive processes and monitoring temperature variations in storage areas. For example, in pharmaceutical manufacturing, temperature monitoring is vital to guarantee product quality and conformity. PIR sensors might well be the way forward for this application. The future will bring, it is hoped, more powerful detectors with longer ranges and wider fields of view.
In the meantime, you can contact our experienced team of engineers for advice on integration, sensor fusion and developments to facilitate heat monitoring automation.

References and Further Reading

Corsi C, History highlights and future trends of infrared sensors, Journal of Modern Optics, 2010: 57(18), p 1663–1686.
Tsai CF, et al. Pyroelectric infrared sensor-based thermometer for monitoring indoor objects. Review of Scientific Instruments. 2003; 74 (12): 5267–5273.
Passive infra-red detectors, Science Daily, Available at: https://www.sciencedaily.com/terms/passive_infrared_sensors.htm Accessed October 2019.
Yang D, et al. Passive Infrared (PIR)-Based Indoor Position Tracking for Smart Homes Using Accessibility Maps and A-Star Algorithm, Sensors 2018, 18, 332.

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