transformer and optical isolation
TRANSCRIPT
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TRANSFORMER AND OPTICAL ISOLATION
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CONTENT
1. Transformer…………………………………………..3
2. Principle of operation……………………………4
3. Isolation transformer…………………………….5-9
4. Optical isolation…………………………………...10-17
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TRANSFORMER:
An A.C. device used to change high voltage low current A.C. into low voltage high current A.C. and vice-versa without changing the frequency.
In brief,1. Transfers electric power from one circuit to another.2. It does so without a change of frequency.3. It accomplishes this by electromagnetic induction.4.Where the two electric circuits are in mutual inductive influence of each other.
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PRINCIPLE OF OPERATION:Transformer works
on the principle of mutual induction of two coils. When current in the primary coil is changed the flux linked to the secondary coil also changes. Consequently an EMF is induced in the secondary coil.
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An isolation transformer is a transformer used to transfer electrical power from a source of alternating current (AC) power to some equipment or device while isolating the powered device from the power source.In theory, the definition of ‘isolation transformer’ applies to any transformer where there is no direct connection between the primary and the secondary windings. In other words: all transformers which are not autotransformers. The windings are connected only by the magnetic flux in the core.
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1. An isolation transformer allows you to establish a separate earth ground...a true earth ground.
2. Isolation transformers are often used to isolate the machine or equipment from the rest of the electrical installation, to avoid loss of power in the case of a first insulation fault.
3. Suitably designed isolation transformers block interference caused by ground loops.
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4. Isolation transformers with electrostatic shields are used for power supplies for sensitive equipment such as computers, medical devices, or laboratory instruments.
5. Isolation transformers can be used to protect people
against the dangers of electric shocks.
6. Isolation transformers block transmission of the DC
component in signals from one circuit to the other, but allow AC components in signals to pass.
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APPLICATIONS
A. MEDICAL TRANSFORMERS:
1. Medical transformers are designed: 2. To isolate the patient and/or the operator
from an electric shock 3. To protect the equipment from power
surges or faulty components
B. PROTECTION OF SENSITIVE EQUIPMENT.
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1. An opto-isolator or optocoupler is used for providing optical isolation.
2. An optical isolator, or optocoupler, is an optical component which allows the transmission of light in only one direction. It is typically used to prevent unwanted feedback into an optical oscillator, such as a laser cavity.
3. Opto-isolators prevent high voltages from affecting the system receiving the signal.
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4. An opto-isolator, also called an optocoupler, photocoupler, or optical isolator, is a component that transfers electrical signals between two isolated circuits by using light.
5. A common type of opto-isolator consists of an LED and a phototransistor in the same opaque package.
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6. An opto-isolator contains a source (emitter) of light(LED), that converts electrical input signal into light, a closed optical channel and a photosensor, which detects incoming light and either generates electric energy directly, or modulates electric current flowing from an external power supply.
7. The LED converts the incoming electrical signal into light and the photosensor detects the incoming light and generates electric energy. There is no direct connection between the LED and photo transistor, they are isolated optically i.e. through light.
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The Basic Theory Optical isolation has two basic elements: a light source (usually a light emitting diode) and a photo-sensitive detector. These two elements are positioned facing one another and inserted in an electrical circuit to form an optocoupler. The key property of an optocoupler is that there is an insulating gap between the light source and the detector. No current passes through this gap, only the desired light waves representing data. Thus the two sides of the circuit are effectively "isolated" from one another.The primary application for optical isolation is in a point-to-point data circuit that covers a distance of several hundred feet or more. Because the connected devices are presumably on different power circuits, a ground potential difference likely exists between them. When such a condition exists, the voltage of "ground" can be different, sometimes by severalhundred volts.
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Where a ground potential difference exists, a phenomenon called ground looping can occur. In this phenomenon, current will flow along the data line in an effort to equalize the ground potential between the connected devices. Ground looping can, at the very least, severely garble communications--if not damages hardware!Optical isolation solves the problem of ground looping by effectively lifting the connection between the data line and "ground" at either end of the line. If an optically coupled connection exists at each end, the data traffic "floats" above the volatility of ground potential differences
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Optical Isolation vs. Transformer Isolation A common belief is that optical isolation is superior to transformer isolation in every case. Theoretically this is true, because optical isolation provides a "true" physical barrier, whereas transformer isolation is a coupling designed to merely "absorb" unwanted frequencies. However, in practice optical isolation is a less efficient transmitter of energy than transformer isolation--an important consideration when signal strength is an issue. Therefore transformer isolation is sometimes the best choice for very long-distance applications. And optical isolation also becomes a prohibitively expensive solution at higher data rates. So in the real world, transformer isolation still has its place.
OPTICAL ISOLATION VS. TRANSFORMER ISOLATION
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ADVANTAGES:
1. Opto – isolators can withstand input-output voltages upto 10kV and voltage transients speed of 10kV / us.
2. They are capable of wideband signal transmission.
3. They work faster in comparison of isolation transformers.
4. They eliminate problems like noise and transient.
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THANK YOU