(B2) Temperature Sensor

Resistance Temperature Detector (RTD) Sensor

temperature sensing devices that use the resistance of a resistor wire to measure temperature

Resistance Temperature Detector (RTD) Sensor

it is a temperature sensing device where as the temperature of metal increases, so does its resistance or the ability of electrons to pass through it.

1. Sensing Element
2. Protecting Tube
3. Process Connection
4. Insulation Material
5. RTD Sensor Wire Configuration
6. Cold End Termination

Parts of an RTD Sensor

Sensing Element

In an RTD sensor, this is the actual temperature sensing metal element.

Protecting Tube

In an RTD sensor, this tube protects the sensing element from the moisture and outside environment. This is made mostly of

Process Connection

includes the standard fitting in an RTD sensor

Insulation Material

provides electrical isolation and durability in an RTD sensor

RTD Sensor Wire Configuration

RTD Sensor is available in 2-wire, 3-wire, and 4-wire configuration

3-wire RTD configuration

it is the most commonly used configuration in an RTD sensor as it is widely used in industrial applications

Cold End Termination

RTD sensor can terminate with the controller like PLC, Closed-loop, PID, etc. through this

1. 2 wire
2. 3 wire
3. 4 wire
4. 4 wire blind loop

Four Types of Wiring Schematics in RTD Wire Configuration

1. Thin-Film RTD Sensors
2. Wire-Wound RTD Sensors
3. Coiled RTD Sensors
4. PT100 RTD Sensors

Types of RTD Sensors

Thin-Film RTD Sensors

The elements consist of a thin metal layer deposited onto a ceramic substrate. This metal film is etched into a specific electrical circuit pattern to provide the desired resistance. Lead wires are then attached, and a protective coating is applied to both the substrate and the element

Wire-Wound RTD Sensors

A wire is coiled around the exterior of a ceramic or glass housing, known as a bobbin. Glass core RTD sensors are suitable for immersion in liquids, while ceramic core RTD sensors are designed to measure extreme temperatures with high accuracy.

Glass Core RTD Sensors

RTD sensors that are suitable for immersion in liquids

Ceramic Core RTD Sensors

RTD sensors that are designed to measure extreme temperatures with high accuracy

Coiled RTD Sensors

Features a fine wire wound into a coil and housed within a ceramic or glass enclosure filled with a non-conductive powder. This design allows the resistance wire to expand and contract with temperature changes, reducing errors from mechanical strain.

PT100 RTD Sensors

This sensor is known for its high accuracy and stability, with minimal drift over time. These come with different temperature coefficients, represented by the Greek letter alpha (α), with the "385" coefficient being the most common.

platinum

The "PT" in the PT100 designation signifies that the sensor uses a __ element

RTD sensors

These are used in various industrial applications, including chemical processing, power plants, food processing, and pharmaceuticals. They are also used in laboratory applications, where accuracy is critical.

RTD sensors

These are ideal for applications that require high accuracy and linearity over a wide temperature range

1. HVAC Systems
2. Process Control
3. Power Generation

Applications of RTD Sensors

HVAC systems

RTD sensors measure temperature in HVAC systems, such as air handling units, boilers, and chillers

Process Control

RTD sensors measure temperature in chemical processing, food processing, and pharmaceuticals

Power generation

RTD sensors measure temperature in power generation equipment, such as turbines and generators

Contact Sensor

When positioned close to an object to be detected for heat or cold, this is used to measure the object's temperature

Thermocouple

A type of temperature sensor that measures temperature based on the voltage generated by the junction of two different metals. It operates on Seebeck effect, which states that when two dissimilar metals are joined at one end and exposed to different temperatures.

Sensing Element

In a thermocouple, when two wires composed of dissimilar metals are joined at both ends and one of the ends is heated, there is a continuous current which flows in the thermoelectric circuit. If this circuit is broken at the center, the net open circuit voltage (the Seebeck voltage) is a function of the junction temperature and the composition of the two metals, which means that when the junction of the two metals is heated or cooled, a voltage is produced that can be correlated back to the temperature.

Seebeck effect

it is the generation of voltage due to a temperature difference between two junctions

1. Hot junction
2. Cold junction
3. Wire Type A
4. Wire Type B
5. Copper Lead Wire

Parts of a Thermocouple

1. Type B
2. Type T
3. Type E
4. Type J
5. Type K
6. Type N
7. Type R & S

Types of Thermocouple

Type B

It is made up of costly platinum-rhodium alloys. The positive leg contains 30% rhodium, and the negative leg contains only 6%. The thermocouple grade wire ranges 32 to 3100°F (0°C to 1700°C)

Type T

It is a very stable thermocouple and is often used in extremely low temperature applications such as cryogen cs or ultra low freezers. It is found in other laboratory environments as well. The type T has excellent repeatability between -380°F to 392°F (-200°C to 200°C)

Type E

These are often referred to as Chromel-Constantan thermocouples. This type has the highest thermoelectric output of common calibrations. Its temperature limitation is within -454°F to 1600°F (-270°C to 870°C)

Type J

It is a thermocouple which is suitable for vacuum, reducing, or inert atmospheres, oxidizing atmosphere. Iron oxidizes rapidly above 538°C (1000°F). Its temperature scalability is limited to -346°F to 1400°F (-210°C to -760 °C)

Type K

These thermocouples are among the most widely used, perhaps due to their relative affordability. These are made up of two nickel-based alloys, Chromel and Alumel. Its thermocouple grade wire rages to -454°F to 2300°F (-270°C to 1260°C)

Type N

These are thermocouples resistant to oxidation and oxidation-related drift issues. Type N thermocouples can handle higher temperatures than type K, and offer better repeatability in the 300°C to 500°C range. Its temperature condition is limited to -454°F to 2300°F (-270°C to 392°C)

Type R & S

These are both recommended for high temperature applications and must be protected with a non-metallic protection tube and ceramic insulators. Temperature limit -58°F to 2700°F (-50°C to 1480°C)

Type B

thermocouple used extensively in the steel and iron industry to monitor temperatures and chemistry through the steel making process

Type C

thermocouple used in high temperatures; used in space vehicles, nuclear reactors, industrial heating; used in high-pressure research; suited for vacuum furnaces

Type E

used in sub-zero oxidizing, or inert applications, and is not subject to corrosion at cryogenic temperatures; ideal for cryogenic, pharmaceutical, and chemical applications

Type J

recommended in vacuum, inert, and reducing atmospheres, as well as hot processes including plastics and resin manufacture

Type K

used for environments such as water, mild chemical solutions, gases, and dry area; found in engines, oil heaters, and boilers, hospitals, and the food industry

Type N

used in vacuum or controlled atmospheres, ovens, furnaces, and kilns; also, gas turbine and engine exhausts and iron, aluminum and smelting industry

Type R & S

used in heat treating and control sensors, semi-conductor industry, glass manufacturing, ferrous and non-ferrous metals

Thermistor

It is a type of resistor whose resistance varies significantly with temperature. It is designed to be sensitive to temperature changes, which makes it useful in various applications like temperature sensing, temperature compensation, and temperature control circuits.

1. Negative Temperature Coefficient (NTC) Thermistors
2. Positive Temperature Coefficient (PTC) Thermistors

Two Main Types of Thermistors (temperature coefficient)

Negative Temperature Coefficient (NTC) Thermistors

type of thermistor where resistance decreases with increasing temperature

Positive Temperature Coefficient (PTC) Thermistors

type of thermistor where resistance increases with increasing temperature

High sensitivity
Fast response
Compact size
Low cost
Accuracy
Easy to use

Advantages of Thermistor

Sensing Element

In a thermistor, the core material (usually a ceramic or polymer composite) that changes resistance with temperature variations

Leads/Terminals

These are metal wires or contacts that connect the thermistor to a circuit for electrical conduction

Encapsulation/Coating

A protective layer made of epoxy, glass, or other insulating materials that shields the thermistor from environmental factors like moisture, dust, and mechanical damage

Electrode

serves as the electrical connection between the thermistor's sensing element and the external circuit

Electrode

allows current to flow through the thermistor, enabling resistance measurement, which varies with temperature

1. Bead-Type
2. Disc Type
3. Probe Type
4. Washer Type

Types of Thermistor

Bead-Type Thermistor

It is a small, high-sensitivity temperature sensor made from metal oxide ceramics, typically coated with glass or epoxy for protection. It offers a fast thermal response and is used in temperature sensing, compensation, and control applications. They are available in NTC and PTC types

Temperature Compensation

a bead-type thermistor is employed in electronic circuits to stabilize performance against temperature fluctuations, such as in amplifiers and oscillators

Disc Type Thermistor

It is a thermally sensitive resistor with a disc-shaped ceramic body, available in NTC or PTC types. Made through sintering metal oxides, it is used in temperature sensing, compensation, and circuit protection due to its stability and efficient heat dissipation.

Temperature Sensing and Measurement

Disc-type NTC thermistors are widely used in temperature sensors for medical, automotive, and industrial applications due to their high sensitivity. They provide precise temperature readings for devices like digital thermometers and HVAC systems

Overcurrent Protection

PTC disc thermistors are commonly used in electronic circuits to protect against overcurrent conditions

Probe Type Thermistor

It is a temperature-sensitive resistor encased in a protective housing, typically designed for immersion, surface, or air temperature sensing applications. The protective probe casing, often made of stainless steel, plastic, or epoxy, enhances durability, ensures accurate readings, and allows for easy integration into various environments.

Industrial Equipment Monitoring

A probe type thermistor is applied in industrial machines to monitor motor and equipment temperatures, preventing overheating

Washer Type Thermistor

It is a thermally sensitive resistor designed in a washer-like shape, typically featuring a central hole that allows it to be mounted onto bolts, screws, or other mechanical fasteners. Their design enables direct thermal contact with surfaces, ensuring accurate temperature measurement or control.

Surface Temperature Sensing

Washer-type thermistors are widely used for measuring surface temperatures or metal components, heat sinks, and industrial equipment

1. Infrared Sensor
2. Semiconductor-based Sensor
3. Bimetallic Strip
4. Fiber Optic Temperature Sensor

Other Temperature Sensors

Infrared (IR) Temperature Sensors

These measure temperature without direct contact by detecting the infrared radiation emitted by objects. Every object with a temperature above absolute zero emits infrared radiation, and the intensity of this radiation depends on the object's temperature. These sensors work by collecting infrared energy through a lens or optical system, converting it into an electrical signal, and processing it to determine temperature

Semiconductor-based Temperature Sensor

These use two integrated circuits with paired diodes, whose voltage and current change with temperature for precise measurement. They provide a linear output but have lower accuracy within 1 to 5°C and a slow response time of 5 to 6 seconds. Operating within -94°F to 302°F (-70°C to 150°C), they are suitable for moderate conditions and commonly used in electronics, industrial monitoring, and HVAC systems

Bimetallic Strip

This is composed of two dissimilar metal strips joined together. The strips are layered on top of each other, with one end joined and the other end free, allowing the assembly to bend and respond to temperature changes. When the strip is exposed to heat, the two dissimilar metals expand at different rates, and the resulting bending is utilized to determine the value of the temperature change

Fiber Optic Temperature Sensor

This uses the properties of light traveling through an optical fiber to measure temperature. Changes in temperature affect the light's intensity, wavelength, or phase shift, which can be detected and analyzed. These sensors are highly sensitive, immune to electromagnetic interference, and suitable for extreme environments, such as high voltage areas, chemical plants, and medical applications