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MAGNETIC AMPLIFIER

Contents Introduction History Amplifier Magnetic amplifier Saturable reactor Principal of magnetic amplifier Working of magnetic amplifier Application, strength & limitation Uses in radio, aircraft & computing Conclusion

INTRODUCTION1.An electromagnetic device for amplifying electrical signal3. A magnetic amplifier uses the principle of transformers along with the concept of magnetic saturation of the core.2.Does not require any moveable part4. The magnetic amplifier has certain advantages over a)high efficiency b)reliability c)ruggedness

HISTORY

1. Developed as early as 1885 in united state2. At that time mainly used for electric

machinery and theater lighting 3. During world war II Germans used it in long

range rockets to regulate frequency output of an a.c. generator

4. Early time its uses as early development of voice transmission by radio.

Amplifier1. An electronic amplifier is an electronic device

that increases the power of a signal.2. It does this by taking energy from a power

supply and controlling the output to match the input signal shape but with a larger amplitude.

3. an amplifier modulates the output of the power supply.

4. There are four basic types of electronic amplifier:-

a) voltage amplifier  b)current  amplifier c)Transconductance amplifier   d)Transresistance amplifier

Magnetic amplifier

1.The magnetic amplifier is an electromagnetic device for amplifying electrical signals2. The magnetic amplifier was invented early in the 20th century3.It was used as an alternative to vacuum tube amplifiers where robustness and high current capacity were required.4. World War 2 Germany used this type of amplifier, and it was used for instance in the V-2 rocket. 5.The magnetic amplifier was most prominent in power control and low-frequency signal applications

The saturable reactor The saturable reactor is the device from

which the magnetic amplifier has been fundamentally developed. The three essential elements of saturable reactor are

The saturable reactor (continued…)

Principal of magnetic amplifier

1. A mag amp device may look like a transformer but the operating principle is quite different from a transformer - essentially the mag amp is a saturable reactor.2. It makes use of magnetic saturation of the core3. For controlled saturation characteristics the magnetic amplifier employs core materials which have a specific B-H curve shape that is highly rectangular, in contrast to the slowly-tapering B-H curve of softly saturating core materials that are often used in normal transformers.

Working1.The typical magnetic amplifier consists of two physically separate but similar transformer magnetic cores each of which has two windings - a control winding and an AC winding.2. A small DC current from a low impedance source is fed into the series-connected control windings. The AC windings may be connected either in series or in parallel, the configurations resulting in different types of mag amps. 3.The amount of control current fed into the control winding sets the point in the AC winding waveform at which either core will saturate. In saturation, the AC winding on the saturated core will go from a high impedance state ("off") into a very low impedance state ("on") - that is, the control current controls at which voltage the mag amp switches "on".

The typical magnetic amplifier circuit shown above has the following components:1.R1 - load resistance2.G - gate winding3.C - control winding4.Ec - excitation 5.Es - input from AC source6.Is - amplified AC current7.Ic - control DC current

Application As modulation and control amplifiers in the early

development of voice transmission by radio.

As voice modulator and magnetic amplifiers were used

in the keying circuits of large high-frequency

alternators used for radio communications.

To regulate the speed of Alexanderson alternators to

maintain the accuracy of the transmitted radio

frequency.

Magnetic amplifiers useful for control of lighting

circuits, for stage lighting and for advertising signs.

Saturable reactor amplifiers were used for control of

power to industrial furnaces.

Strength a static device with no moving parts

no wear-out mechanism

has a good tolerance to mechanical shock and vibration.

It requires no warm-up time.

Multiple isolated signals may be summed by additional

control windings on the magnetic cores.

The windings of a magnetic amplifier have a higher tolerance

to momentary overloads than comparable solid-state devices.

The magnetic amplifier is also used as a transducer in

applications such as current measurement and the flux gate

compass

Limitations The gain available from a single stage is limited and low

compared to electronic amplifiers.

Frequency response of a high gain amplifier is limited to

about one-tenth the excitation frequency

Solid-state amplifiers can be more compact and efficient than

magnetic amplifiers.

The bias and feedback windings are not unilateral, and may

couple energy back from the controlled circuit into the control

circuit.

This complicates the design of multistage amplifiers when

compared with electronic devices.

Usage in radio

Magnetic amplifiers were used voice modulation.

The alternator's frequency limits were rather

low to where a frequency multiplier had to be

utilized to generate higher radio frequencies

than the alternator was capable of producing.

Even so, early magnetic amplifiers incorporating

powdered-iron cores were incapable of

producing radio frequencies above

approximately 200 kHz.

Usage in aircraft Magnetic amplifiers were used in aircraft systems

(avionics ) before the advent of high reliability

semiconductors.

They were important in implementing early auto land

systems

for the control of its engine air intakes before

subsequent development of a replacement system using

digital electronics.

Usage in computing

Magnetic amplifiers were widely studied during

the 1950s as a potential switching element for

mainframe computers.

Mag amps could be used to sum several inputs in

a single core, which was very useful in the

arithmetic logic unit (ALU).

The mag amp was able to combine the

advantages of tubes and transistors in an era

when the latter were expensive and unreliable.

conclusion

Although, magnetic amplifier is an outdated

technology in present trend, It is the first device which can replace fragile vacuum tube in almost all its function. It has good mechanical strength and

maintenance free.

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