UNIT-3
WATTMETER
Dynamometer type wattmeter:
A dynamometer type wattmeter is most commonly employed for measurement of power in a.c as well as d.c circuits.
3.1Principle of Dynamometer type wattmeter:
It is based on the principle that mechanical force exists between two current carrying conductors.
3.2Construction of Dynamometer type wattmeter:
It essentially consists of two coils, namely fixed coil and moving coil. The fixed coil is split into two equal parts which are placed close together and parallel to each other. The moving coil is pivoted between the two fixed coils and is placed on the spindle to which the pointer is attached. the fixed coils are connected in series with the load and carry the circuit current. It is, therefore called current coil. The moving coil is connected across the load and carries current proportional to the voltage. It is therefore called potential coil. Generally, a high resistance is connected in series with potential coil to limit the current through it. The controlling torque is provided by springs which also serve the additional purpose of leading current into and out of the moving coil. Air friction damping is employed in such instruments.
Dynamometer type wattmeter
3.3Working of Dynamometer type wattmeter:
When power is to be measured in a circuit, the instrument is suitably connected in the circuit. The current coil is connected in series with load so that it carries the circuit current. The potential coil is connected across the load so that it carries current proportional to the voltage. Due to the current in the coils, mechanical force exists between them. The result is that the moving coil, moves the pointer over the scale. The pointer comes to rest at a position where deflecting torque is equal to the controlling torque. Reversing the current, reverses the field due to fixed coil as well as the current in the moving coil so that the direction of the deflection torque remains unchanged. Therefore, such instruments can be used for the measurement of a.c as well as d.c power.
UNIT -4
ENERGYMETER
4.1ENERGYMETER-
The meter which is used for measuring the energy utilises by the electric load is known as the energy meter. The energy is the total power consumed and utilised by the load at a particular interval of time. It is used in domestic and industrial AC circuit for measuring the power consumption. The meter is less expensive and accurate.
4.2 SINGLE PHASE ENERGY ENERGY METER
The principle of working and construction of induction type meter is very simple and easy to understand that’s why these are widely used in measuring energy in domestic as well as the industrial world. In all induction meters, we have two fluxes which are produced by two different alternating currents on a metallic disc. Due to alternating fluxes, there is an induced emf, the emf produced at one point (as shown in the figure given below) interacts with the alternating current of the other side resulting in the production of torque.
Similarly, the emf produced at the point two interacts with the alternating current at point one, resulting in the production of torque again but in opposite direction. Hence due to these two torques which are in different directions, the metallic disc moves. This is the basic principle of working of an induction type meters.
4.3DIGITAL ENERGYMETER 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.). Meters for smaller services (such as small residential customers) can be connected directly in-line between source and customer. For larger loads, more than about 200 amps of load, current transformers are used, so that the meter can be located other than in line with the service conductors . The meters fall into two basic categories, electromechanical and electronic. This paper dwells on the electronic meter (i.e. the digital meter)
UNIT-5
MEASURING INSTRUMENTS
5.1MEGGAR- The Megger insulation tester is a small, portable instrument that gives you a direct reading of insulation resistance in ohms or megohms. For good insulation, the resistance usually reads in the megohm range.
A current transformer (CT) is a type of transformerthat is used to measure alternating current (AC). It produces a current in its secondary which is proportional to the current in its primary. Current transformers, along with voltage or potentialtransformers, are instrument transformers.
UNIT-6
ELECTRONIC INSTRUMENTS
CRO
The cathode ray oscilloscope is an electronic test instrument, it is used to obtain waveforms when the different input signals are given. In the early days, it is called as an Oscillograph. The oscilloscope observes the changes in the electrical signals over time, thus the voltage and time describe a shape and it is continuously graphed beside a scale. By seeing the waveform, we can analyze some properties like amplitude, frequency, rise time, distortion, time interval and etc.
UNIT-7
LCR METER
LCR METER
An LCR meter is a type of electronic test equipment used to measure the inductance (L), capacitance (C), and resistance (R) of an electronic component[1]. In the simpler versions of this instrument the impedance was measured internally and converted for display to the corresponding capacitance or inductance value. Readings should be reasonably accurate if the capacitor or inductor device under test does not have a significant resistive component of impedance. More advanced designs measure true inductance or capacitance, as well as the equivalent series resistance of capacitors and the Q factor of inductive components.
UNIT-8
TRANSDUCERS
8.1 INTRODUCTION
A device that converts variations in a physical quantity, such as pressure or brightness, into an electrical signal, or vice versa.
UNIT-9
MEASURMENT OF TEMPRATURE
9.1 THERMOMETER
A thermometer is a device that measures temperature or a temperature gradient. A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb of a mercury-in-glass thermometer or the digital sensor in an infrared thermometer) in which some change occurs with a change in temperature; and (2) some means of converting this change into a numerical value (e.g. the visible scale that is marked on a mercury-in-glass thermometer or the digital readout on an infrared model). Thermometers are widely used in technology and industry to monitor processes, in meteorology, in medicine, and in scientific research.
MCQ
Q.1 Dynamometer wattmeter can measure power in a a-single phase a.c circuit b-a.c or d.c circuit c- d.c circuit
Q.2 Speed of disc of an energy meter is kept low at full loadto reduce a-eddy current b- friction error c-self braking torque d-all of these
Q-3 Where terminal of a meggar are open it will read a-Zero b-infinity c-100 ohms d-1kohm
SHORT ANSWER QUESTION
Q.1 Generated test voltage in a meggar is 500/100v , why?
Q.2 For a unity power factor prove that w1=w2
Q-3 Define and classify transducer.
LONG ANSWER QUESTION
Q.1 What a strain gauge? Describe its working.
Q.2 Explain working of LVDT.
Q.3 What is a thermocouple?
Q.4 Describe construction and working of a meggar.
Q.5 Describe construction and working of an earth tester.
Q.6 Describe construction and working of a synchroscpe.