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Sunday, December 19, 2010

What are Electrical Transducers?

                          The transducers that convert the mechanical input signals of the physical quantity into electrical output signals are called as electrical transducers. The input given to the electrical transducers can be in the form of the displacement, strain, velocity, temperature, flow etc and the output obtained from them can be in the form of current, voltage and change in resistance, inductance and capacitance. The output can be measured easily and it is calibrated against the input, thus enabling the measurement of the value of the input.

Here are some of commonly used electrical transducers:

1) Potentiometers: They convert the change in displacement into change in the resistance, which can be measured easily.

2) Bridge circuits: These convert the physical quantity to be measured into the voltage.

3) Wheatstone bridge: It converts the displacement produced by the physical quantity to the current in the circuit.

4) Capacitive sensors or Variable Capacitance Transducers: These comprise of the two parallel plates between which there is dielectric material like air. The change in distance between the two plates produced by the displacement results in change in capacitance, which can be easily measured.

5) Resistive sensors or Variable Resistance Transducers: There is change in the resistance of these sensors when certain physical quantity is applied to it. It is most commonly used in resistance thermometers or thermistors for measurement of temperature.

6) Magnetic sensors: The input given to these sensors is in the form of displacement and the output obtained is in the form of change in inductance or reluctance and production of the eddy currents.

7) Piezoelectric transducers: When force is applied to these transducers, they produce voltage that can be measured easily. They are used for measurement of pressure, acceleration and force.
Industrial Piezoelectric transducers

8) Strain gauges: When strain gauges are strained or stretched there is change in their resistance. They consist of the long wire and are able to detect very small displacements produced by the applied force or pressure.

9) Photo electric transducers: When the light is applied to these transducers they produce voltage.

10) Linear variable differential transformer (LVDT): LVDT is the transformer consisting of the primary and the secondary coil. It converts the displacement into the change in resistance.

11) Ultrasonic Transducers: These transducers use the ultrasonic or ultrasound waves to measure parameters like fluid level, flow rate etc.
Ultrasonic transducer

Apart from these there are some more electrical type of transducers like moving coil type, changing dielectric type, changing core positions type etc.

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Types of Transducers : Mechanical Transducers:

           There are various types of transducers depending upon the change in property or the energy they bring about to measure specified physical quantities. The transducers used for the measurement systems are broadly classified into following categories: mechanical and electrical. Let use see these in details.

The mechanical transducers are the mechanical elements that are used for converting one form of energy into other form that can be measured easily. There are number of mechanical transducers, some of the commonly used ones are described below:

1) Bellows: These are the elastic elements that convert the air pressure into displacement, and it is commonly used for the measurement of pressure.

A Bellow

2) Bourdon tube: This elastic tube converts air pressure to the rotary motion of the pointer used to indicate the pressure.

A Bourden tube

3) Spring: The spring tend to expand when force is applied to them, thus they are used for the measurement of force.

4) Proving rings: Like the springs the proving rings also convert applied force to the displacement.

5) Diaphragm: It converts applied pressure to the displacement.

6) Manometer: The manometer converts the applied pressure into variable displacement of the liquid within it enabling to measure the pressure.

7) Thermocouple: Thermocouple is the devise that produces electric current when one of its end is heated. The current produce by the devise can be measured, which can be calibrated against the temperature enabling us to measure the temperature of the body.
A thermocouple

8) Bimetals: These are the bimetallic strips comprising of two different metals having different coefficient of thermal expansion, joint together. When the strip is heated one metal expands lesser while the other metal expands more leading to the deflection of the bimetallic strip, which is converted into the rotary motion of the pointer that indicates the temperature.

9) Hydropneumatic transducers: These include devices like orifice, venturi, pitot tube, vanes and turbines that are used for measurement of pressure, velocity, flow rate and force of water.

Apart from the mechanical transducers mentioned above there are many others like seismic mass, pendulum scale, float etc. Most of the mechanical transducers are used as the primary transducers, meaning the initial input is applied to them, while the output obtained from them can be used directly to measure the quantity or it can be given as input to the secondary transducer, which are mostly of electrical type.

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Types Of Sensors Used In Engineering Applications

                  A number of different types of sensors are used within the engineering industry. Commonly, this includes sensors such as tension load cells, eddy-current sensors, and many other to monitor and keep track of laser displacement, pressure, vision, and color. Of course this is just the tip of the iceberg and all sensors vary in regards to their usages.
A pressure transducer

The first bridge circuit-measuring device created for measuring electrical resistances, was originally invented by Samuel Hunger Christie.

Subsequent to its release, most did not have interest until the English physicist; Sir Charles Wheatstone further developed and promoted it within the following year. Ensuing, these improvements and following a boost in popularity it became known as the Wheatstone bridge.

The bridge circuit design, works similar to the original potentiometer.Mainly, it works by balancing two legs within the bridge circuit, consisting of one leg for the measurement of an unknown electrical resistance, while the other consists of the unknown component.

Often, it is used for the measurement of resistance changes that occur within strain gages. The device design commonly consists of a flexible and insulated backing, used in the support of a foil pattern.

After attaching the device to an object by use of an adhesive, a Wheatstone bridge is commonly used to measure the resistance change that occurs during the time the foil and object become deformed.

The first bonded resistor wire strain gage was not developed until 1938. During this time, Arthur C. Ruge and Edward E. Simmons created the device in order to measure the amount of strain within an object. In most cases, a load cell uses four strain gauges according to a Wheatstone bridge configuration.

This is referred to as a strain gauge load cell, which is the most common. However, most of the load cells consist of the Wheatstone bridge configuration, which offers the ability for measurements such as compression, shear force, and tension.

Tension Load Cells

A load cell works as a transducer in order to convert force into an electrical measureable output. The conversion takes place within an indirect and two-stage process.

Tension load cells tend to come in a range of different sizes and styles. In addition, they also vary for the limits they have. Some of the high capacity load cells can hold up to 2 million pounds. Furthermore, some of them offer a combination of compression and tension within one unit.

Eddy Current

With the eddy current technologies, people are capable of taking measurements, called inductive measurements from energy that comes from an oscillating circuit.

With this type of set up a coil of an alternating current is supplied, which in turn causes the formation of a magnetic current around the coil. Anything with an electrical current placed within the magnetic field causes the reaction called the eddy current.

One of the advantages with this type of process has to do with how a large number of electrically conductive, nonferromagnetic, and ferromagnetic metals can be used with this principle. In addition, the sensor is small compared to many others that are out there. In addition, it has a high temperature range as well as high accuracy.

Vision, Colour Sensors, and laser displacement sensors

Vision and colour sensors work together with other pieces within an application in order to ensure that everything goes as planned.

Each of the sensors are sensitive to a minute amount of detail and can ensure that the application acquires the right amount set to a number of different criteria. This allows for faster manufacturing than would be possible with the human eye.

In certain cases, this is attained through the combination of several sensors within one application. One of the names referred to for such a system is virtual system architecture. This allows for several sensors to work together within one application.

Laser displacement sensors are another type of non contact sensor. With the laser technologies, there is a laser diode that projects a visible portion of light onto the object that is currently being measured.

Any movement of the object having the light projected on it, causes the digital processing of the information.

These are just a few of the sensors used in the engineering industry today, but I am sure you can see the massive importance and potential of such devices in shaping the way we accurately limit or measure a number of fundamental properties and values.

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What is the Difference Between Transducers and Sensors?

A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument.

A transducer is a device, usually electrical, electronic, electro-mechanical, electromagnetic, photonic, or photovoltaic that converts one type of energy or physical attribute to another for various purposes including measurement or information transfer.

Transducers are machines used to change one type of energy into another. They can often be found as a component of more complex devices. Sensors are explicitly intended to measure and express levels of measurement. Quite often, sensors are composed of transducers; therefore, one can see how easy it can be to confuse the two.
Different sensors and transducers

Generally, transducers come in basic varieties of which there are almost endless applications. The first variety is contact transducers. This type is categorized by a single point of contact used to detect energy. There is generally a coupling material, such as water or oil, employed in order to prevent distortion between the source of energy and the point of detection.

Many sensors utilize contact transducers in order to detect energy levels and convert that into an electrical energy which would then influence a display meter. One type of contact transducer that was almost ubiquitous in the late 1980s and early 1990s were tape heads. These were found in any cassette player, touching the magnetic tape and reading the magnetic information that was on it. This information was then converted to an electric signal that was carried by wire to speakers or headphones and then converted back into sound waves.

The second most common type of transducers is the immersion type. These are intended to work in liquid environments. This type is effective at measuring sound, pressure, or other forms of mechanical energy. Paintbrush transducers are used like immersion types are, but they work in open environments and have highly sensitive crystals to detect even the faintest levels of energy. Antennae for radio waves are paintbrush types as they collect the broadcast radio waves and convert them into electrical energy that is converted back into sound by a radio’s speakers.

While transducers are specialized components used in machines to gather and convert types of energy, sensors are devices with a single purpose. Like transducers, they detect physical levels and many of them use transducers to do this, especially those that measure energy; but unlike transducers their purpose is exclusively to measure these levels and display that measurement in a form legible to people. Transducers are invaluable to this process because they can convert levels measured into basic forms of energy, like electrical, which can be displayed digitally or with an analog meter.



Basics of Instrumentation & Control

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To view more posts on PRESSURE : CLICK HERE


To view more posts on FLOW : CLICK HERE


To view more posts on LEVEL : CLICK HERE


To view more posts on TEMPERATURE : CLICK HERE

Analytical Instrumentation

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