Relay and Transducers

Relays and

Transducers

Relays

-an electrically operated switch that uses electromagnet to mechanically operate a switch.

Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts.Relays allow one circuit to switch a second circuit which can be completely separate from the first.

Types of Relays1. Latching relay2. Reed relay3. Mercury relay4. Polarized relay5. Machine tool relay

8. Contactor9. Solid state contactor

relay10. Buchholz relay11. Overload protection

relay

Latching relayis a two-position electrically-

actuated switch. It is controlled by two momentary-acting switches or sensors, one that 'sets' the relay, and the other 'resets' the relay. The latching relay maintains its position after the actuating switch has been released, so it performs a basic memory function.

Reed relayA reed relay is a reed

switch enclosed in a solenoid. The switch has a set of contacts inside an evacuated or inert gas-filled glass tube which protects the contacts against atmospheric corrosion; the contacts are made of magnetic material that makes them move under the influence of the field of the enclosing solenoid or an external magnet.

  is a type of relay that uses an electromagnet to control one or more reed switches. The contacts are of magnetic material and the electromagnet acts directly on them without requiring an armature to move them. Sealed in a long, narrow glass tube, the contacts are protected from corrosion, and are usually plated with silver, which has very low resistivity but is prone to corrosion when exposed, rather than corrosion-resistant but more resistive gold as used in the exposed contacts of high quality relays. The glass envelope may contain multiple reed switches or multiple reed switches can be inserted into a single bobbin and actuate simultaneously. 

Mercury relayA mercury relay is a relay that

uses mercury as the switching element. They are used where contact erosion would be a problem for conventional relay contacts. Owing to environmental considerations about significant amount of mercury used and modern alternatives, they are now comparatively uncommon.

Polarized relayA relay which responds to the

direction of the currentenergizing it.A relay which responds to the direction of the current,voltage, power, or the like, energizing it. Also calleddirectional relay.

Machine tool relayA machine tool relay is a type

standardized for industrial control of machine tools, transfer machines, and other sequential control. They are characterized by a large number of contacts (sometimes extendable in the field) which are easily converted from normally-open to normally-closed status, easily replaceable coils, and a form factor that allows compactly installing many relays in a control panel. 

ContactorA contactor is a heavy-duty

relay used for switching electric motors and lighting loads, but contactors are not generally called relays. Continuous current ratings for common contactors range from 10 amps to several hundred amps. High-current contacts are made with alloys containing silver. 

Solid state contactor relayA solid state contactor is a

heavy-duty solid state relay, including the necessary heat sink, used where frequent on/off cycles are required, such as with electric heaters, small electric motors, and lighting loads. 

Buchholz relayA Buchholz relay is a safety

device sensing the accumulation of gas in large oil-filled transformers, which will alarm on slow accumulation of gas or shut down the transformer if gas is produced rapidly in the transformer oil. The contacts are not operated by an electric current but by the pressure of accumulated gas or oil flow

Overload protection relayElectric motors need overcurrent

protection to prevent damage from over-loading the motor, or to protect against short circuits in connecting cables or internal faults in the motor windings. The overload sensing devices are a form of heat operated relay where a coil heats a bimetallic strip, or where a solder pot melts, releasing a spring to operate auxiliary contacts. These auxiliary contacts are in series with the coil. If the overload senses excess current in the load, the coil is de-energized.

Relays are used wherever it is necessary to control a high power or high voltage circuit with a low power circuit. The first application of relays was in long telegraph systems, where the weak signal received at an intermediate station could control a contact, regenerating the signal for further transmission. High-voltage or high-current devices can be controlled with small, low voltage wiring and pilots switches. Operators can be isolated from the high voltage circuit. Low power devices such as microprocessors can drive relays to control electrical loads beyond their direct drive capability. In an automobile, a starter relay allows the high current of the cranking motor to be controlled with small wiring and contacts in the ignition key.

Advantages of relays:Relays can switch AC and DC, transistors can only switch DC.Relays can switch high voltages, transistors cannot.Relays are a better choice for switching large currents (> 5A).Relays can switch many contacts at once.

Disadvantages of relays:Relays are bulkier than transistors for switching small currents.Relays cannot switch rapidly (except reed relays), transistors can switch many times per second.Relays use more power due to the current flowing through their coil.Relays require more current than many chips can provide, so a low power transistor may be needed to switch the current for the relay's coil.

Transducers is a device that converts

one form of energy  to another form of energy. Usually a transducer converts a signal in one form of energy to a signal in another.

Types of Transducers1. Transom mount Transducers2. Dual element Transducers3. Delay line Transducers4. Contact Transducers5. Immersion Transducers6. Through-Hull Transducers

Transom mount Transducers

As the name implies, transom mount transducers are installed on the boat's transom, directly in the water and typically sticking a little below the hull.

Dual element Transducers contain two independently operated elements in a single housing. One of the elements transmits and the other receives the ultrasonic signal.

Delay line transducers As the name implies, the

primary function of a delay line transducer is to introduce a time delay between the generation of the sound wave and the arrival of any reflected waves.

Contact transducers  are used for direct contact inspections, and are generally hand manipulated. They have elements protected in a rugged casing to withstand sliding contact with a variety of materials. These transducers have an ergonomic design so that they are easy to grip and move along a surface. They often have replaceable wear plates to lengthen their useful life. Coupling materials of water, grease, oils, or commercial materials are used to remove the air gap between the transducer and the component being inspected.

Immersion Transducers do not contact the component.

These transducers are designed to operate in a liquid environment and all connections are watertight. Immersion transducers usually have an impedance matching layer that helps to get more sound energy into the water and, in turn, into the component being inspected. 

Through-Hull Transducers 

Through-hull transducers are mounted through a hole drilled in the bottom of the boat and protrude directly into the water.

Applications:Electromagnetic:

Antenna Magnetic cartridge Hall effect sensor

Electroacoustic:Loudspeaker, earphone Microphone Tactile transducer Hydrophone

Electro-optical (Photoelectric):

Fluorescent lampIncandescent lamp Light-emitting diode Laser Diode Photodiode, photoresistor, phototransistor.Cathode ray tube (CRT)

Prepared by:Abarquez, Wendilyn T.

Salumag, Karl A.