Transcript CHAPTER-2
MEASUREMENT DEVICES OUTLINE Multimeters Analog Multimeters Digital Multimeters Breadboard Oscilloscope Signal Generator Clamp Meter Voltage Transformer Current Transformer MEASUREMENT DEVICES MULTIMETERS • A multimeter also known as a VOM (Volt-Ohm meter), is an electronic measuring instrument that combines several measurement functions in one unit. To measure voltage (ac, dc), current (ac, dc) and resistance, two types of instruments, analog and digital meters, are utilized. Analog Multimeters • The main part of an analog multimeter is the D’Arsonval meter movement also known as the permanent-magnet moving-coil (PMMC) movement. It have multiple scales on the dial, a moving needle and many manual settings on the function switch. MEASUREMENT DEVICES MULTIMETERS Analog Multimeters – Operating principle MEASUREMENT DEVICES MULTIMETERS Analog Multimeter Scales and Zero Position Adjustment • A typical analog multimeter has several scales. As illustrated in following, each scale consists of a curved line that is marked off into sections or divisions. A range identifies the high and low limits of a scale. • The zero adjustment should not normally need to be touched, but it may vary slightly with time and temperature. Adjustment should be made with the meter not in use and it should be gently adjusted with a screwdriver to ensure the meter is properly zeroed. MEASUREMENT DEVICES MULTIMETERS The Measurement of Current, Voltage and Resistance Using Analog Multimeters • When using an analog multimeter, measurements for voltage, current and resistance need to be made in different ways. To illustrate the way in which these different tests can be made using an analog multimeter, the simple circuit shown below will be used: MEASUREMENT DEVICES MULTIMETERS Digital Multimeters • In laboratory, due to we will use digital multimeters, digital multimeters are very important more than analog multimeter. • For AC measurements, the digital multimeter is a true rms instrument that it measures true rms value of any periodic signal MEASUREMENT DEVICES Measuring DC Voltage Using Digital Multimeter • • • • Connect the black test lead to the COM jack and the red test lead to the V jack. Set the range switch at the desired V range position. Connect test leads across the source or load under measurement. You can get a reading from LCD display. The polarity of the red lead connection will be indicated along with the voltage value. • • When only the figure ‘1’ is displayed, it indicates overrange situation and the higher range has to be selected. When the value scale to be measured is unknown beforehand, set the range selector at the highest position. MEASUREMENT DEVICES Measuring AC Voltage Using Digital Multimeter • • • • • Connect the black test lead to the COM jack and the red test lead to the V jack. Set the range switch at the desired V range position. Put down the "DC/AC" button, meter will be transformed to the AC measuring state. Connect test leads across the source or load under measurement. You can get a reading from LCD display. • • When only the figure ‘1’ is displayed, it indicates overrange situation and the higher range has to be selected. When the value scale to be measured is unknown beforehand, set the range selector at the highest position. MEASUREMENT DEVICES Measuring DC Currents Using Digital Multimeter • • • • Connect the black test lead to the COM jack and the red test lead to the A jack for a maximum of 400mA current. For a maximum of 10A, move the red lead to the 10A jack. Set the range switch at the desired A range position. Connect test leads in series with the load under measurement. You can get reading from LCD. The polarity of red connection will be indicated along with the voltage value. • • • When only the figure ‘1’ is displayed, it indicates overrange situation and the higher range has to be selected. When the value scale to be measured is unknown beforehand, set the range selector at the highest position. A socket is 250mA, the maximum current of 10A socket is 12.5A, over-current will destroy the fuse. MEASUREMENT DEVICES Measuring AC Currents Using Digital Multimeter • • • • • Connect the black test lead to the COM jack and the red test lead to the A jack for a maximum of 400mA current. For a maximum of 10A, move the red lead to the 10A jack. Set the range switch at the desired A range position. Put down the "DC/AC" button, meter will be transformed to the AC measuring state. Connect test leads in series with the load under measurement. You can get reading from LCD. • • • When only the figure ‘1’ is displayed, it indicates overrange situation and the higher range has to be selected. When the value scale to be measured is unknown beforehand, set the range selector at the highest position. A socket is 250mA, the maximum current of 10A socket is 12.5A, over-current will destroy the fuse. MEASUREMENT DEVICES Measuring Resistance and Continuity Test • Connect the black test lead to the COM jack and the red test lead to the Ω jack. • Set the range switch at the desired Ω range position. • Connect test leads across the resistance under measurement. • You can get reading from LCD. MEASUREMENT DEVICES Measuring Capacitance • Connect the black test lead to the COM jack and the red test lead to the jack. • Set the range switch at the desired F range position and press “L/C” button down. • Before connect test leads across two sides of the capacitor under measurement, be sure that the capacitor has been discharged fully. • You can get reading from LCD. MEASUREMENT DEVICES Measuring Inductance • Connect the black test lead to the COM jack and the red test lead • to the H jack. • Set the range switch at the desired H range position and press “L/C” button down. • Connect test leads across two sides of the inductor under • measurement. MEASUREMENT DEVICES Testing Diode • Connect the black test lead to the COM jack and the red test lead to the V jack. (The polarity of red lead is “+”) • Set the range switch at the range position. • Connect the red lead to the anode, the black lead to the cathode of the diode under testing. • You can get reading from LCD. • The meter will show the approximate forward voltage drop of the diode. MEASUREMENT DEVICES Testing Transistor • Set the rotary switch at the hFE range position. • Put two plugs of multifunction testing equipment (spare parts) into COM jack and V jack. • Identify whether the transistor is NPN or PNP type and insert emitter, base and collector leads into the proper holes of the transistor on the multifunction testing equipment (spare parts) for testing. • You can get reading from LCD. MEASUREMENT DEVICES Changing the fuse and battery in Digital Multimeters MEASUREMENT DEVICES The differences between Analog and Digital Multimeter • Analog multimeters give the output as a reading on a scale against a pointer, while digital multimeter output is in numerical form displayed on a LCD. • Analog multimeters give a continuous output and carry a greater uncertainty in the measurement (about 3%), while digital multimeter measurements have a far less uncertainty (about 0.5% or less). Digital multimeters are more accurate than analog multimeters. • Digital multimeters have a better range of measurements than analog multimeters. • Digital multimeters offer additional features such as capacitance, temperature, frequency, sound level measurements and detection of semiconductor device pins (transistor / diode). • Analog multimeters have to be calibrated manually, while most digital multimeters are calibrated automatically before every measurement. • Analog multimeters have to be set for the specific range of measurement manually, while some must digital multimeters have auto ranging feature. • Analog multimeters require practice to take good measurements, while digital multimeters can be operated even by an untrained person. • Analog multimeters are less costly while digital multimeters are expensive. MEASUREMENT DEVICES BREADBOARD • A breadboard is a simple way to quickly create and change a developing circuit, often called a prototype circuit. Parts are just inserted into the same column of the breadboard to connect them. Metal clips underneath the breadboard connect the wires or component leads. MEASUREMENT DEVICES MEASUREMENT DEVICES MEASUREMENT DEVICES CADET MEASUREMENT DEVICES OSCILLOSCOPE • An oscilloscope is a voltage sensing electronic instrument that is used to visualize certain voltage waveforms. • An oscilloscope can display the variation of a voltage waveform in time on the oscilloscope’s screen. • Most oscilloscopes have at least two input channels and each channel can display a waveform on the screen. Multiple channels are useful for comparing waveforms. Diffrent waveforms (sine, square, triangle, DC voltage) Amplitude measurement Phase diffrence measurement Frequency measurement The obtain characteristic curves of semi-conductor circuit elements such as diode, transistor The obtain of charge and discharge curves of condansators Oscilloscope is NOT measure current MEASUREMENT DEVICES OSCILLOSCOPE MEASUREMENT DEVICES OSCILLOSCOPE MEASUREMENT DEVICES MEASUREMENT DEVICES MEASUREMENT DEVICES MEASUREMENT DEVICES MEASUREMENT DEVICES Signal Generator MEASUREMENT DEVICES Signal Generator MEASUREMENT DEVICES Signal Generator MEASUREMENT DEVICES Signal Generator MEASUREMENT DEVICES Voltage Transformer • A transformer is an electrical device that transfers energy from one circuit to another purely by magnetic coupling. • Relative motion of the parts of the transformer is not required for transfer of energy. • If a loads is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load • Transformers are often used to convert between high and low voltages, to change impedance, and to provide electrical isolation between circuits. MEASUREMENT DEVICES Clamp Meter • It is simple to measure very high currents (hundreds of amperes) with the appropriate current transformer. • The electric current in the conductor to be measured, without having to make physical contact with it, or to disconnect it for insertion through the probe. Accurate measurement of low currents (a few milliamperes) with a current transformer clamp is more difficult. • Clamp meter is only measure RMS value of sine wave. Other waveforms readings will be incorrect. MEASUREMENT DEVICES Current Transformer •A current transformer (CT) is used for measurement of electric currents. •The CT is isolate the circuit from high voltage side and is protect to the circuit. •Current transformers are commonly used in metering and protective relays in the electrical power industry. MEASUREMENT DEVICES CADET