What is a Temperature Sensor?

Summary

This video explores the various types of temperature sensors used in industries, including RTDs, thermocouples, thermistors, and semiconductor sensors. It explains how these sensors work, their applications, and the importance of transforming temperature readings into electrical signals. The video highlights the different advantages and limitations of each technology, such as accuracy, sensitivity, and cost. Viewers will also learn about the role of temperature transmitters in converting tiny sensor signals into universally accepted electrical ranges. Ultimately, the video aims to help viewers choose the best temperature sensor for specific needs based on performance factors.

Takeaways

• 😀 Temperature sensors are used in various industries and applications to measure temperature, including in reactors and electrical machines.
• 😀 Different types of temperature sensors exist because each technology has its advantages and disadvantages depending on the application.
• 😀 A temperature sensor or transducer transforms physical variables like temperature into an electrical signal, which is then processed by the system.
• 😀 A temperature transmitter converts the tiny electrical signal from a temperature transducer into standardized signal ranges like 4-20 mA, 1-5 V, etc.
• 😀 RTDs (Resistance Temperature Detectors) are passive devices that measure temperature by measuring the resistance change as temperature varies.
• 😀 The most common RTD is PT100, made from platinum, which is linear in its resistance-temperature relationship and has a wide temperature range from -330°F to 1560°F.
• 😀 Thermistors, which can be NTC or PTC, are temperature-dependent resistors used for applications like overcurrent protection and heating elements.
• 😀 Thermocouples generate millivolt signals based on the thermoelectric effect, with no external excitation required, and are used for high-temperature applications like furnaces and turbine combustion chambers.
• 😀 Thermocouples have lower accuracy than RTDs and require a cold junction to complete the circuit, with different types like Type J and Type K suited to various temperature ranges.
• 😀 Semiconductor temperature sensors are based on diode junctions and are useful in electronic devices, but have a limited temperature range of -40°F to 248°F.
• 😀 When selecting a temperature sensor, factors like accuracy, sensitivity, cost, and application requirements play a critical role in choosing the right technology.

Q & A

What is the role of a temperature sensor or temperature transducer?

A temperature sensor or transducer transforms the physical property of temperature into an electrical signal, which can then be measured and processed.

What is the difference between a temperature sensor and a temperature transmitter?

A temperature sensor or transducer converts temperature into a small electrical signal, while a temperature transmitter amplifies and converts this signal into a universally accepted electrical signal range such as 4-20 mA, 1-5 V, or 0-10 V.

What is the main reason for using different types of temperature sensors in various applications?

Different temperature sensors are suited to specific applications due to their unique characteristics, such as accuracy, sensitivity, and temperature range, which make some sensors better than others for certain tasks.

What is an RTD (Resistance Temperature Detector) and how does it work?

An RTD is a temperature sensor whose resistance varies with temperature. It requires an external current to generate a voltage drop across it, and this voltage is used to determine the temperature.

Why is it important to minimize the external current applied to an RTD?

Minimizing the external current applied to an RTD is crucial to prevent excessive power dissipation in the resistor, which could lead to excess heat and measurement errors.

What is the difference between a 2-wire, 3-wire, and 4-wire RTD configuration?

A 2-wire RTD is the simplest and involves measuring the voltage drop across the RTD. In a 3-wire or 4-wire configuration, additional wires are added to compensate for the resistance of the wiring, thereby reducing measurement errors.

What are thermistors, and how do they differ from RTDs?

Thermistors are temperature-dependent resistors, which can either have a Negative Temperature Coefficient (NTC) where resistance decreases with temperature, or a Positive Temperature Coefficient (PTC) where resistance increases with temperature. Unlike RTDs, thermistors are often used in applications such as overcurrent protection or self-regulating heating elements.

What are the main applications of thermocouples?

Thermocouples are commonly used in high-temperature environments such as furnaces, gas turbine combustion chambers, and exhaust ducts. They are self-powered and do not require an external excitation current.

What is a significant drawback of thermocouples compared to RTDs?

A significant drawback of thermocouples is their lower accuracy compared to RTDs. Additionally, thermocouples require a reference measurement point, called a cold junction, which can complicate their use.

What is the temperature range and sensitivity of a Type K thermocouple?

A Type K thermocouple, made of Chromel-Alumel, has an operating range of −330°F to +2460°F, with a sensitivity of approximately 22.8 µV/°F.

What are the advantages and limitations of semiconductor temperature sensors?

Semiconductor temperature sensors are small, cost-effective, and have a linear characteristic, making them ideal for electronic devices and IC technologies. However, their temperature range is limited, typically from -40°F to 248°F, restricting their use in extreme environments.