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
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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
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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
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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
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Comparing the advantages and disadvantages of the two types instruments. The accuracy of null type of instruments is higher than that of deflection type. This is because the opposing effect is calibrated with the help of standards which have high degree of accuracy. On the other hand, accuracy of deflection type of instruments is dependent
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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
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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
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A stepper motor control is a specially constructed DC motor. It has 4 windings arranged such that instead of running in the usual continuous fashion the motor rotates in precise steps, from one fixed position to another. The common step sizes range from 0.9 to 30 degrees. The stepping action is achieved by proper combination
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Microcontrollers as the name suggests, are small controllers. They are like single chip computers that often embedded into other systems to function as processing / controlling unit, microcontrollers are single chip microcomputers. A microcontroller has a CPU (a microprocessor) in addition to a fixed amount of RAM, ROM and I/O parts and a timer on
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Microprocessor – controlled temperature system is used to Read the temperature in a room Display the temperature at LCD/LED panel Turn-on a fan if the temperature is above the limit. Turn-on a heater if the temperature is below the limit. This system has a temperature sensor as an input device to sense room temperature and
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