Rongge

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...

Classification of Measuring Instruments Measuring instruments may be broadly classified as follows 1.        Absolute instruments 2.        Secondary instruments (a)      Indicating instruments (b)      Integrating instruments  (c)      Recording  instruments Absolute and secondary instruments   Absolute instruments: “absolute instruments are those which gives the value of the quantity to be measured, in terms of the constants of the instruments and their deflection only”. Such instruments do not require any previous calibration or comparison. Example: Tangent galvanometer (is a very common example) and Rayleigh’s current balance instruments. Uses: These instruments used as standardizing instruments in laboratories. Secondary instruments: “secondary instruments are those in which the value of electrical quantity to be measured can be determined from the...