Operational amplifier description

 Operational amplifier 

An operational amplifier (op-amp) is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output.^[1] An op-amp produces an output voltage that is typically hundreds of thousands of times larger than the voltage difference between its input terminals.^[2]
Operational amplifiers had their origins in analog computers, where they were used to do mathematical operations in many linear, non-linear and frequency-dependent circuits. Characteristics of a circuit using an op-amp are set by external components with little dependence on temperature changes or manufacturing variations in the op-amp itself, which makes op-amps popular building blocks for circuit design.
Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer, industrial, and scientific devices. Many standard IC op-amps cost only a few cents in moderate production volume; however some integrated or hybrid operational amplifiers with special performance specifications may cost over $100 US in small quantities.^[3] Op-amps may be packaged as components, or used as elements of more complex integrated circuits.
The op-amp is one type of differential amplifier. Other types of differential amplifier include the fully differential amplifier (similar to the op-amp, but with two outputs), the instrumentation amplifier (usually built from three op-amps), the isolation amplifier (similar to the instrumentation amplifier, but with tolerance to common-mode voltages that would destroy an ordinary op-amp), and negative feedback amplifier (usually built from one or more op-amps and a resistive feedback network).

Circuit notation

 

The circuit symbol for an op-amp is shown to the right, where:

• V₊: non-inverting input
• V₋: inverting input
• V_out: output
• V_S+: positive power supply
• V_S−: negative power supply

The power supply pins (V_S+ and V_S−) can be labeled in different ways (See IC power supply pins). Often these pins are left out of the diagram for clarity, and the power configuration is described or assumed from the circuit.

Operation

The amplifier's differential inputs consist of a V₊ input and a V₋ input, and ideally the op-amp amplifies only the difference in voltage between the two, which is called the differential input voltage. The output voltage of the op-amp is given by the equation:

Alarm circuit description

Description

Here is a simple but effective burglar alarm circuit that can be fixed on windows to detect break through. The circuit uses a fine wire element fixed as a network through the window  glass  for sensing the break through . Normally the base of Q1 is held to ground potential by the wire element.So Q1 will be off and SCR H1 will not be conducting,and horn will be off.When the  wire element is broken the base of Q1 will be raised to positive potential, Q1 will be on and so SCR H1 (TYN 612) will be ON making the horn to blow and this condition will be latched by the SCR.The circuit remains ON until the normal condition is restored or the power supply is switched OFF.

Circuit Diagram with Parts List

 

Winding installation in semi-closed slots

A slot closure for the semi-closed slots of the stator of an electric machine is disclosed. The slot closure comprises slot closing bars interconnected in a ladder-like arrangement by flexible strips. Flexing of the strips by about 90 permits them to be successively inserted edge-wise through the slot openings. Advantageously, the ladder-like arrangement of bars and strips is made of a moldable or stampable material.

** Why AC systems are preferred over DC systems?

Ans :
Due to following reasons, AC systems are preferred over DC systems:

a. It is easy to maintain and change the voltage of AC electricity for transmission and distribution.

b. Plant cost for AC transmission (circuit breakers, transformers etc) is much lower than the equivalent DC transmission

c. From power stations, AC is produced so it is better to use AC then DC instead of converting it.

d. When a large fault occurs in a network, it is easier to interrupt in an AC system, as the sine wave current will naturally tend to zero at some point making the current easier to interrupt.