BROOKDALE ELEC 103 - Analog and Digital Meters Devices and Measurements

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Meters 23 July 2005Professor Andrew H. Andersen 1ELEC 103Analog and Digital Meters Devices and Measurements23 July 2005 Meters 2Objective• At the conclusion of this presentation the student will describeand identify:– Safety precautions when using test equipment– Analog Multimeters– Digital Multimeters– How to connect a voltmeter to a circuit to measure voltage– How to connect an ammeter to a circuit to measure current– How to connect an ohmmeter to measure resistance• The student will be able to:– Read voltage from an analog voltmeter– Read current from an analog ammeter– Read resistance from an analog ohmmeterMeters 23 July 2005Professor Andrew H. Andersen 223 July 2005 Meters 3Basic Circuit Measurements• A voltmeter measures voltage across (in parallel) a resistance or load• An ammeter is inserted in the current path (in series) to measure current• Resistance is measured across a resistor, out-of-circuit, with an ohmmeter• Digital Multimeters (DMM’s) measure voltage, current and resistance with the same connections as the analog meter23 July 2005 Meters 4Electrical Test Equipment - The Multimeter• A multimeter is a single piece of text equipment that may be used to measure voltage, current or resistance, depending upon the function selected– Analog mulitmeters have both range and function switches– Digital multimeters are usually autoranging– A voltmeter is used to measure voltage across a component or circuit– An ammeter is used to measure current through a circuit– An ohmmeter is used to measure resistanceMeters 23 July 2005Professor Andrew H. Andersen 323 July 2005 Meters 5Typical d’Arsonval Meter Movement23 July 2005 Meters 6Meter Deflection is Proportional to CurrentMeters 23 July 2005Professor Andrew H. Andersen 423 July 2005 Meters 7A Typical Seven Segment Display23 July 2005 Meters 8Examples of Meter Displays and SymbolsEach of the above may be used to represent either an ammeter (A), a voltmeter (V), or an ohmmeter (Ω)Meters 23 July 2005Professor Andrew H. Andersen 523 July 2005 Meters 9Typical Portable Multimeters23 July 2005 Meters 10Example of a Digital and Analog MultimeterMeters 23 July 2005Professor Andrew H. Andersen 623 July 2005 Meters 11Typical Digital Multimeters (DMM)23 July 2005 Meters 12A Typical Analog MultimeterMeters 23 July 2005Professor Andrew H. Andersen 723 July 2005 Meters 13Selecting the Proper Range on an Analog MeterSelect a range for maximum deflection of the pointer23 July 2005 Meters 14A Simpson 260 Analog MultimeterMeters 23 July 2005Professor Andrew H. Andersen 823 July 2005 Meters 15Schematic Symbols for MetersThe analog voltmeter and ammeter must be connected to the circuit with proper polarity to avoid damaging the meter movementThe ohmmeter may only be used on unenergized components23 July 2005 Meters 16Voltage Measurements• To measure voltage, the voltmeter is placed in parallel across the component; that is, one lead is place on each side of the component• Set an analog voltmeter to the highest range when measuring an unknown voltage• Then switch to the next lowest rage until maximum deflection of the pointer is obtained while remaining on the scaleMeters 23 July 2005Professor Andrew H. Andersen 923 July 2005 Meters 17A Voltmeter Connected to Measure Voltage23 July 2005 Meters 18Current Measurements• To measure current, the ammeter must be placed in series with the component; that is, it must be in line with the current path• Usually, power is removed from the circuit before connecting or removing the ammeter• Set an analog ammeter to the highest range when measuring an unknown current• Then switch to the next lowest rage until maximum deflection of the pointer is obtained while remaining on the scaleMeters 23 July 2005Professor Andrew H. Andersen 1023 July 2005 Meters 19An Ammeter Connected to Measure Current23 July 2005 Meters 20Resistance Measurements• To measure resistance– If necessary circuit power must be removed – Usually at least one lead of the component must be removed from the circuit– the ohmmeter is connected across a componentMeters 23 July 2005Professor Andrew H. Andersen 1123 July 2005 Meters 21Ohmmeter Connection to Measure ResistanceReading the Analog MeterMeters 23 July 2005Professor Andrew H. Andersen 1223 July 2005 Meters 23Example 1Assume that the VOM shown is on the AC/DC 6 V scale. What is the reading?23 July 2005 Meters 24000ACDCACDC0005010 2521100 20 410 4 2150 30 6200 40 820 8 4250 50 102510 5300 60 123012 6ANALOG MULTIMETER AC AMPSdBmdBmOHMS01234510202050OHMS1k AC AMPS1042024681011Example 1 SolutionAssume that the VOM shown is on the AC/DC 6 V scale. What is the reading?4.5 VNote that the reading is made on the 60 V scale and the user places the decimal.Meters 23 July 2005Professor Andrew H. Andersen 1323 July 2005 Meters 25Example 2Assume that the VOM shown is on the AC AMPS 3 A scale. What is the reading?23 July 2005 Meters 26000ACDCACDC0005010 2521100 20 410 4 2150 30 6200 40 820 8 4250 50 102510 5300 60 123012 6ANALOG MULTIMETER AC AMPSdBmdBmOHMS01234510202050OHMS1k AC AMPS1042024681011Example 2 SolutionAssume that the VOM shown is on the AC AMPS 3 A scale. What is the reading?1.25 ANote that the reading is made on the 30 A AC scale and the user places the decimal place.Meters 23 July 2005Professor Andrew H. Andersen 1423 July 2005 Meters 27Example 3When you change resistance scales on a VOM, what must first be done before measuring a resistor?23 July 2005 Meters 28Example 3 SolutionWhen you change resistance scales on a VOM, what must first be done before measuring a resistor?Zero the meter by shorting the leads together and adjusting the Zero Adjust control.Meters 23 July 2005Professor Andrew H. Andersen 1523 July 2005 Meters 29Example 4Assume that the VOM shown is on the Ω x100 scale. What is the reading?23 July 2005 Meters 30Problem 4 SolutionAssume that the VOM shown is on the Ω x100 scale. What is the reading? 340ΩNote that the reading is made on the Ω scale and the user multiplies the reading by


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