Rongge

Working of D.C Generator As explained before the D.C generator converts mechanical energy into electrical (D.C) energy. The generator is usually coupled to a prime-mover. The prime-mover may be a diesel/petrol engine, or a turbine depending upon the rating and application of the generator. The prime-mover converts some sort of energy (diesel/petrol/water/steam/gas etc.) into mechanical energy. This mechanical energy is supplied to the generator (i.e. generator input). Working of D.C Generator If the generator is very small for commercial purpose i.e. for a shop or small work shop or cinema etc. the prime-mover is a diesel engine. If the generator is very big like in power stations then the prime-mover will be a turbine. Again depending upon the resources the turbine may be a water turbine, steam turbine, gas turbine etc. When the prime-mover output is given to the generator, the generator armature starts rotating. Usually the poles on the yoke are made of permanent magnets. Therefore, ...

Pointers and Scales in Measuring Instruments Instrument scales and pointers may be considered together in two classes: (A)     Those intended for reading quickly (in the case of switch board instruments at a distance), and (B)      Those intended for close accurate reading for portable instruments. Pointers: The shape and size of the pointers depends upon the type of instrument. The weight and inertia of pointer must be reduced so as to reduce the load on the bearing and to avoid necessity of damping torque. The pointer motion is usually limited by buffer stops little more than the scale. These stops are constructed as very light springs so that the pointer is not bent when it strikes them sharply on a sudden overload or reversal of the operating current. fig 1. Pointer The pointers for switch board and panel instruments should be so that the position of the pointer is conspicuous. The pointers are usually broad or carry broad targets at their ends. Al...

Differential Amplifier A differential amplifier serves to amplify the difference between tow signals. A differential amplifiers forms the basic stage of an integrated op-amp with differential inputs. The circuit diagram of the emitter coupled differential amplifier is shown in the below fig. it uses two identical npn transistors. The transistors are connected in CE mode. The emitter bias is used here. The two inputs V 1 and V 2 and the output is V o . The output is derived from the two collector points. If the inputs are similar, the output of the amplifier is zero. The amplifier outputs V 1 and V 2 . Therefore it is called as differential amplifier. The emitter coupled differential amplifier of the below fig possess the following properties. Emitter Coupled Differential Amplifier 1.        Low drift. 2.        Very high input resistance. 3.        Cancels the effects of supply voltages. 4. ...