Santhakumar Raja

Primary standards : These standards are always fixed standards, single valued. The campbell type of primary standard is shown in fig. It consists of a single layer primary coil of bare copper wire wound under tension in grooves machined in a cylinder of marble. The primary coil is divided into two parts. The two parts

The secondary standard of Emf is the unsaturated Weston cell. Unsaturated Weston Cell Construction and Characteristics. The construction of an unsaturated cell is shown in fig. The unsaturated cell is similar to a saturated cell except that it does not have the cadmium sulphate crystals (CdSO4). It has the same electrodes but the solution is

The primary standard of luminous intensity in a full radiator (black body or Planckian radiator) at the temperature of solidification of platinum (2.042°k approximately) under a pressure of 101.325 kN/m². The “candela” is then defined as one sixtieth of luminous intensity per square metre of one full radiator. Secondary standards of luminous intensity are special

Secondary instruments work in two modes: (i) Analog mode, and (ii) Digital mode. Signals that vary in a continuous fashion and take on an infinite number of values in any given range are called analog signals. The devices which produce these signals are called analog devices. In contrast, the signals which vary in discrete steps

In a null type of instrument, a zero or null indication leads to determination of the magnitude of measured quantity. The null condition is dependent upon some other known conditions. In contrast to deflection type of instruments, a null type instrument attempts to maintain the deflection at zero by suitable application of an effect opposing

The instruments of this type, the deflection of the instrument provides a basis for determining the quantity under measurement. The measured quantity. produces some physical effect with deflects or produces a mechanical displacement of the moving system of the instrument. An opposing effect is built in the instrument which tries to oppose the deflection or