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Indicating, Intergrating and Recording Instruments Measuring instruments (i.e. secondary instruments) may be classified according to their function as: 1.        Indicating instruments 2.        Integrating instruments 3.        Recording instruments 1.        Indicating instruments: “Indicating instruments are those which indicate the magnitude of an electrical quantity at the time when it is being measured.” Their indications are given by a pointer moving over calibrated dial. Example: Ordinary voltmeters, ammeters and wattmeter’s, etc. 2.        Integrating instruments: “Integrating instruments are those which measure and register by a set of dials and pointer either the total quantity of electricity (In amp-hours) or the total amount of electrical energy (in watt-hours or kWh) supplied to a circuit in a given time.” Example: The ampere...

Introduction to Electrical Measuring Instruments The instruments, which are used to measure electrical quantity such as current, voltage, power, energy, frequency, power factor etc. are called Electrical Measuring Instruments. These instruments are generally named after the electrical quantity to be measured. Thus the instruments which measure current voltage, power, energy and frequency are known as ammeter voltmeter, wattmeter, energy meter and frequency meter respectively. The accuracy, convenience and reliability of electrical instruments are mainly responsible for the wide spread use of electrical methods of measurements. The various types of indicating instruments along with their suitability for the type of measurements, type of control, type of damping, special features and applications are given in the below table S.No Type of Instrument Suitability of measurements Type of control Type of Damping 1 Moving iron DC or AC measurements (current & voltage) Spring o...

Errors in Moving Coil Instruments The errors that usually occur in PMMC instruments are 1.        The frictional error. 2.        Temperature error. 3.        The error owing weakening of permanent magnet. 4.        Stray magnetic field error. 5.        Thermo-electric error. 6.        Observational error. 1.        The frictional Error: The friction of the pivot in the jewel produces a frictional torque which affects the instrument reading. This error is more serious for sensitive instruments designed for low operating torque. Remedy: The frictional error in PMMC instruments can be produced by providing proper pivoting and balancing i.e. these errors may be reduced by adopting a moving system of light construction and large deflecting torque. 2.      ...

Introduction to measuring instruments Measurements play an important role in achieving goals and objectives of Engineering . Measurements are basically a means of communication and are used by scientists for understanding natural phenomenon, by the society for transacting business and by the engineers for practical ends. The advancement of science and technology is dependent upon a parallel progress in measurement techniques. The reason for this are obvious. The importance of measurement is simply and eloquently expressed in the following statement of the famous physicist Lord Kelvin. “ I often say that when you can measure what you are speaking about and can express it in numbers, you know something about it; when you cannot express in it numbers your knowledge is of a meagre and unsatisfactory kind.” Measurement is essentially a process in which the magnitude of a quantity is determined in comparison with another similar quantity. Measurements involve the use of instruments as a phy...

Advantages and Disadvantages of Moving Coil Instruments Advantages: 1.        Uniform scale. 2.        High sensitivity 3.        Low power consumption. 4.        No hysteresis loss. 5.        Not much affected by stray magnetic fields. 6.        Very effective and efficient eddy current damping. 7.        High torque / weight ratio. 8.        Very accurate and reliable. 9.        Can be used in vertical and horizontal position due to spring control and 10.     Can be designed to cover a wide range of currents and voltages by using shunt and series resistances respectively Disadvantages: 1.        Can be used only for D.C measurements. 2.        Mo...