Topic:

Temperature Transducer

Group Members

M.Faizan-Ul-Hassan 13EL34 (Leader)

Asim Raza 13EL08

M.Imran Firdos 13EL09

ContentsTransducerTemperature Transducer• Principle • Working• ApplicationsTypesRTD (Resistance Temperature Detector)ThermocoupleThermistors

Introduction

What is a Transducer?

A transducer is a device that converts a signal in one form of energy to another form of energy.

For example, a stereo speaker converts the electrical signals of recorded music into sound. 

Energy types include (but are not limited to) electrical, mechanical, electromagnetic (including light), chemical, acoustic and thermal energy.

BLOCK DIAGRAM OF TRANSDUCERS

 Transducer contains two parts that are closely related to each other i.e. the sensing element and transduction element.

The sensing element is called as the sensor. It is device producing measurable response to change in physical conditions.

The transduction element convert the sensor output to suitable electrical form.

What Is Temperature Transducer ?

It is a temperature monitoring device.A device in an automatic temperature-control system that converts the temperatur

e into some other quantity.

Principle

Principle

A temperature transducer is an electrical device usually used in automated air-temperature control sequences. Its purpose is to take a measurement of the air temperature and relay the information after translating it into a readable form to a power source for the mechanical part of the system.

Working

A temperature transducer is an electrical device usually used in automated air-temperature control sequences. Its purpose is to take a measurement of the air temperature and relay the information after translating it into a readable form to a power source for the mechanical part of the system.

Sensor

Once the information has been taken by the temperature transducer and relayed, the information is sent to the unit power source. Usually, when a transducer is telling a mechanical unit, such as a furnace or a cooling system, that it needs to engage in order to create the desired temperature, it will also tell the unit when it has reached that desired temperature.

Instructions

When the unit power source reveals the information from the temperature transducer, it either tells the system to stand idle or engage depending on the temperature that has been measured. If the temperature reads lower than the setting input to the system by the user, the heating unit is told to engage until the air is measured by the temperature transducer to be as high in temperature as the user desires.

Digital Display

Temperature transducers send the information they collect to more sources than just the power source for the heating or cooling unit. Digital thermostats installed in many households and businesses utilize digital LCD screens to display the information that is read by the temperature transducer. The transducer measures the air temperature and translates it into information the screen is able to display at the same time the information is being sent to the power source telling it whether or not to engage.

Working Diagram

Applications

Steel industry

Monitor temperature and chemistry throughout the steel making process

Heating appliance safety

Thermocouples in fail-safe mode are used in ovens and water heaters to detect if pilot flame is burning to prevent fire and health hazard

Manufacturing

Used for testing prototype electrical and mechanical apparatus

Process plants

Chemical production plants and refineries use computer programs to view the temperature at various locations. For this situation, a number of thermocouple leads are brought to a common reference block.

Types Of Temp. Transducer

RTD(Resistance temperature detector)

Principle

An RTD is basically a temperature sensitive resistor

it is a positive temperature coefficient device

As like thermocouple it doesn’t produce any voltage by itself

it is used in electrical appliances such as motors, generators

Resistance temperature detector

Applications

 It is widely used in furnaces for automatic temperature measurement.

 Due to its compactness, it replaces conventional thermometers as well as thermocouples thus eliminating the use of lots of wires.

Used in medical and chemical laboratories to detect very low temperatures (like dry ice and liquid nitrogen)

 Due to electrical output it is used wherever feedback system is required and corrective action is thus taken in an automated system.

Resistance temperature Detect0r

Advantages Disadvantages

Linearity over a wide operating range

Low sensitivity

Wide operating range It can be affected by contact resistance, shock and vibration.

Higher temperature operation Requires no point sensing

Better stability at high temperature

Higher cost than other temperature transducers

Thermocouple

It is a type of temperature sensor, which is made by joining two dissimilar metals at one end.

The joined end is referred to as the HOT JUNCTION. The other end of these dissimilar metals is referred to as the COLD END or COLD JUNCTION.

If there is a difference in temperature between the hot junction and cold junction, a small voltage is created.

This voltage is referred to as an EMF (electro-motive force) and can be measured and in turn used to indicate temperature.

Thermocouple Applications

Applications

Temperature Measurement 

Power Generation 

Radiation Sensors

 Gas Safety Equipment's

Manufacturing Industry 

Thermocouple

Advantages Disadvantages

It has rugged construction Cold junction and other compensation is essential for accurate measurements

It has a temperature range from -270 c -2700 c

They exhibit n0n-linearity in the emf versus temperature characteristics

Bridge circuit are not required for temperature measure

To avoid stray electrical signal pickup, proper separation of extension leads from thermocouple wire is essential

Comparatively cheaper in cost Stray voltage pick-up are possible

Calibration checks can be easily performed

In many applications, the signals need to be amplified

Thermistor

A thermistor is a type of resistor with resistance varying according to its temperature. The resistance is measured by passing a small, measured direct current through it and measuring the voltage drop produced.

There are basically two broad types 1. NTC-Negative Temperature Coefficient: used mostly in temperature sensing 2. PTC-Positive Temperature Coefficient,: used mostly in electric current control.

Thermistor

Advantages DisadvantageSmall size and low cost Non-linearityFast response over narrow temperature range

Self-heating

Good sensitivity in the NTC region Moisture failure(non-glass only)

Applications of Thermistor

PTC NTCused as current-limiting devices for circuit protection

are regularly used in automotive applications

used as heating elements in small temperature-controlled ovens

 used as resistance thermometers in low-temperature measurements of the order of 10 K.

used as heater in automotive industry to provide additional heat inside cabin with diesel engine or to heat diesel in cold climatic conditions before engine injection.

 used as inrush-current limiting devices in power supply circuits

used to monitor the temperature of an incubatorused in the Food Handling and Processing industry, especially for food storage systems and food preparation

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