Mumbai University > Electronics and Telecommunication > Sem3 > Electronic Instruments and Measurements

Marks: 10M

Year: June 15

Power –

Power is the rate at which energy is supplied (or energy per unit time). Power is measured in watts. One watt is equal to one joule supplied per second. It is the flow of energy at any one time and is measured in Watts. Equipment and appliances are rated on a basis of Watts, and the amount of energy generated by equipment, or the amount consumed by equipment and appliances is measured in Watt-hours.

Energy –

Energy is referred to as the ability to do work. Energy is measured in units called joules, J, or in watt hours as shown below. One kilojoule, kJ is equal to a thousand joules, and one mega joule, MJ, is equal to a million joules. Watt hours (Wh), are a convenient way of measuring electrical energy. One watt-hour is equal to a constant one watt supply of power supplied over one hour (3600 seconds). If a bulb is rated at 40watts, in one hour it will use 40 Wh, and in 8 hours it will use 320 Wh of energy.

Working of an Energy Meter –

• An electric meter or energy meter is a device that measures the amount of electrical energy supplied to or produced by a residence, business or machine.

• Modern electricity meters operate by continuously measuring the instantaneous voltage (volts) and current (amperes) and finding the product of these to give instantaneous electrical power (watts), which is then integrated against time to give energy used (joules, kilowatt-hours etc).

• The meters fall into two basic categories, electromechanical and electronic.

• The most common type of electronic electric meter is the watt-hour meter. It uses solid-state circuits that produce electrical signals whose frequency or strength is proportional to the voltage and current being used

• These signals are converted into energy measurements recorded by mechanical or electronic indicators. Electronic watt-hour meters are generally more expensive than electromechanical models, but are more accurate

• They can provide features such as the ability to record separately the energy consumed during different times of day and the ability to report meter readings by means of signals sent through the power lines to the power company.