What Is An Example Of A Thermal Device?

Thermal devices are instruments that are used to measure temperature. They work by detecting changes in temperature and converting this information into data that can be quantified and analyzed. Thermal devices have a wide range of applications across many industries including manufacturing, food processing, medicine, and scientific research.

Thermal devices allow users to monitor temperatures in environments and systems where getting direct temperature readings might be difficult or even dangerous. The data from thermal devices can help identify problems or inefficiencies in processes and machinery. Thermal devices are often critical components of control systems that regulate heating, cooling, and other temperature-dependent operations.

Some common types of thermal devices include thermocouples, thermistors, infrared sensors, and resistance temperature detectors (RTDs). Each type uses different physical properties to determine temperature. Later sections will provide more details on how each of these thermal devices work.

Types of Thermal Devices

There are several different categories of thermal devices that are commonly used for temperature measurement and control. Here is an overview of some of the main types:

Thermocouples

Thermocouples consist of two wires made from different metals joined at one end. When the junction is heated or cooled, a voltage is produced that correlates to temperature. Thermocouples are inexpensive, durable, and have a wide temperature range.

Thermistors

Thermistors are resistors that change resistance value based on temperature fluctuations. There are two main types: NTC (negative temperature coefficient) thermistors that decrease in resistance as temperature rises, and PTC (positive temperature coefficient) thermistors that increase resistance as temperature rises.

Infrared Sensors

Infrared sensors measure infrared energy emitted from an object to determine its temperature. They can measure temperature without contact, making them useful for moving objects or hazardous environments.

Resistance Temperature Detectors

RTDs contain a resistor that changes resistance value based on temperature change. RTDs provide greater accuracy and repeatability compared to thermocouples and thermistors.

Thermocouples

A thermocouple is a thermal device that consists of two different conductors that generate a voltage proportional to a temperature difference. Thermocouples operate on the principle of the Seebeck effect, which states that when two dissimilar metals are joined, a voltage is produced if the junctions are at different temperatures.

The two conductors are called thermoelements and are usually made from metals like iron, nickel, copper, platinum, and chromel. The thermoelements are welded together at one end to form a junction called the hot or measurement junction. This junction is where the temperature is measured. The other end of the thermoelements lead to the cold junction which is connected to the voltmeter. The temperature difference between the hot and cold junctions generates a voltage that can be measured by the voltmeter.

As the hot junction’s temperature changes, the voltage changes proportionally, allowing the thermocouple to measure temperature. The magnitude of voltage depends on the types of metals used in the thermoelements. By knowing the Seebeck coefficients of the thermoelement materials, the temperature can be determined from the measured voltage.

Thermocouples are a simple, versatile and rugged sensor used to measure a wide temperature range. They are low cost and do not require an external excitation source. Some applications include appliances, HVAC equipment, automobiles and industrial processes.

Thermistors

Thermistors are another type of thermal device that measures temperature changes through variations in electrical resistance. They are made from semiconductor materials such as metal oxides, typically composed of nickel, manganese, cobalt, copper, or iron. The resistance of a thermistor changes significantly with minute differences in temperature.

Thermistors function on the principle that the electrical resistance of a semiconductor changes exponentially according to its temperature. The hotter a thermistor becomes, the more electrical resistance it provides. The material composition and structure of a thermistor determines whether it has a negative temperature coefficient (NTC), meaning resistance decreases as temperature rises, or a positive temperature coefficient (PTC), meaning resistance increases with temperature.

NTC thermistors are typically used in circuits where smaller precision temperature measurements are required, such as in temperature compensation circuits and measurement instruments. NTC thermistors allow for more precise temperature control due to their heightened sensitivity. PTC thermistors are more commonly used in circuits for temperature measurements, overcurrent protection, and self-regulating heating. The exponential change in resistance allows PTC thermistors to restrict current flow once a temperature threshold is reached.

Overall, thermistors provide an inexpensive and compact way to obtain very accurate temperature measurements. Their sensitivity also allows them to detect minute temperature differences and changes quickly. This makes thermistors ideal for use in various temperature monitoring and control applications.

Infrared Sensors

Infrared sensors are a type of thermal device that detect infrared radiation to measure temperature. Infrared radiation, sometimes called infrared light, is electromagnetic radiation with wavelengths longer than visible light that we cannot see with our eyes. All objects emit some level of infrared radiation correlated to their temperature. Infrared sensors work by detecting this infrared radiation.

Infrared sensors contain special materials that are sensitive to infrared wavelengths. When infrared radiation hits these sensor materials, the materials absorb the infrared energy, causing vibrations among their molecules and a resulting increase in temperature. This change in temperature generates an electrical signal proportional to the infrared radiation level and therefore the temperature of the object being measured.

One common type of infrared sensor uses a pyroelectric material that generates a temporary voltage when heated by infrared radiation. Another variety contains thermopiles made up of thermocouples. As infrared radiation heats one side of the thermopile, the temperature difference causes a voltage. In both cases, the electrical signal can be processed to calculate the corresponding temperature of the object emitting the original infrared radiation.

Infrared sensors allow temperature measurement from a distance without contact with the object being monitored. This makes them useful for applications such as fever screening, fire detection, motion sensing, night vision devices, and even some spectroscopy and astronomy tools.

Resistance Temperature Detectors

Resistance Temperature Detectors (RTDs) are temperature sensors that contain an electrical resistor that changes resistance value as its temperature changes. An RTD sensor contains a pure metal or alloy, like platinum, nickel or copper. As the temperature increases, the material’s electrical resistance increases as well. This predictable change in resistance can be precisely correlated to determine temperature.

RTDs work by running a small constant current through the RTD element. As the temperature changes, the resistance changes, which causes a corresponding change in the voltage drop across the device. This voltage change is measured and converted into a temperature reading using the known resistance vs. temperature relationship of the RTD element. The higher the temperature, the higher the measured resistance.

RTDs provide very accurate and repeatable temperature measurements. They are slower to respond than thermocouples but are stable over a wide temperature range. RTDs also have a near linear resistance/temperature curve, enabling precise temperature measurement. They are commonly used for precision temperature measurement in industrial and scientific applications.

Thermal Imagers

Thermal imagers, also known as infrared cameras, are devices that detect infrared radiation to see variations in temperature. They operate based on the principle that all objects emit a certain amount of electromagnetic radiation that is invisible to the human eye. The radiation emitted is proportional to an object’s temperature – hotter objects emit more.

Thermal imaging cameras contain an infrared detector that absorbs this infrared radiation. The detector has tiny sensors, each of which records the intensity of infrared radiation hitting it. The greater the intensity, the hotter that part of the object is. An electrical signal is generated with a voltage that varies based on the amount of infrared radiation. This signal is then sent to a transducer which converts it into an image that can be viewed digitally.

A thermal imaging camera displays this information in the form of an image called a thermogram. In a thermogram, different colors represent different temperatures. For example, black may indicate cold temperatures while white would represent hot temperatures. This allows you to visualize the thermal variations and patterns across the target object, referred to as a thermal signature. The cameras can detect temperature differences as small as .02 degrees Celsius which allows for very accurate imaging and profiling.

Thermal imagers have a variety of applications including building inspections, preventative maintenance, firefighting, and industrial monitoring. They are particularly useful because they allow one to see objects or areas that may be obscured visually but are distinguishable based on temperature differences.

Applications

Thermal devices have a wide range of applications in various industries and fields. Here is an overview of some of the most common uses for these devices:

HVAC Systems: Thermal devices like thermistors and RTDs are extensively used in HVAC (heating, ventilation and air conditioning) systems. They help monitor and control air temperatures to maintain desired comfort levels in buildings and motor vehicles.

Manufacturing: Infrared temperature sensors are often used in manufacturing processes to monitor temperatures of raw materials and finished products. This allows precise control over industrial ovens and quality assurance procedures.

Medicine: Infrared thermal imagers can detect minute temperature differences on the skin, which aids in medical diagnosis. They help locate inflammation, abnormal tissue growths, and circulatory problems.

Military: Thermal weapon sights and infrared imaging systems are used to detect and identify targets based on their heat signatures. This allows operations at night or in low visibility conditions.

Research: Highly precise thermocouples and RTDs are used in scientific research to measure temperatures of various materials and phenomena – from chemical reactions to the Earth’s atmosphere.

Consumer Electronics: Thermistors help regulate current flow and act as resettable fuses in devices like computers and mobile phones to prevent overheating damage.

Pros and Cons

Thermal devices each have their own unique advantages and disadvantages that make them suitable for different applications. Here is a comparison of the pros and cons of some common thermal devices:

Thermocouples

Pros:

• Inexpensive
• Small in size
• Fast response time
• Wide temperature range

Cons:

• Low accuracy and stability
• Require cold junction compensation
• Low sensitivity and voltage output

Thermistors

Pros:

• High sensitivity and resolution
• Stable and accurate
• Low cost

Cons:

• Limited temperature range
• Non-linear output

Infrared Sensors

Pros:

• Non-contact temperature measurement
• Fast response time
• Wide temperature range

Cons:

• Lower accuracy than contact sensors
• Requires a clear optical path to target
• More expensive

Conclusion

Thermal devices have wide applications for temperature measurement and control across many industries. The main types covered here include thermocouples, thermistors, infrared sensors, resistance temperature detectors, and thermal imagers. Each type has its own advantages and limitations in terms of accuracy, sensitivity, temperature range, speed of response, size, and cost.

Thermocouples are versatile and inexpensive but have lower accuracy. Thermistors can be very precise with excellent stability. Infrared sensors allow non-contact temperature measurement. RTDs also provide high accuracy and stability. Thermal imagers produce heat maps and profiles across surfaces. Choosing the right thermal device depends on the specific application and requirements.

In summary, thermal devices utilize temperature-dependent properties of materials to measure temperature. Advancements in materials science and electronics continue to improve the capabilities and applications of these essential technologies for temperature sensing and control.