Analog and Digital Meters

Transcription

1 Analog and Digital Meters Devices and Measurements Objective At the conclusion of this presentation the student will describe and 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 ohmmeter 5 February Meters

2 Basic 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 5 February Meters 3 Electrical Test Equipment - The Multimeter A multimeter is used to measure voltage, current or resistance, depending upon the function selected 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 resistance 5 February Meters

3 Typical d Arsonval Meter Movement 5 February Meters 5 Meter Deflection is Proportional to Current 5 February Meters 6

4 A Typical Seven Segment Display 5 February Meters 7 Examples of Meter Displays and Symbols Each of the above may be used to represent either an ammeter (A), a voltmeter (V), or an ohmmeter (Ω) 5 February Meters 8

5 Typical Portable Multimeters 5 February Meters 9 Example of a Digital and Analog Multimeter 5 February Meters 1

6 Typical Digital Multimeters (DMM) 5 February Meters 11 A Typical Analog Multimeter 5 February Meters 1

7 Selecting the Proper Range on an Analog Meter Select a range for maximum deflection of the pointer 5 February Meters 13 Measuring a Resistor Remove power if necessary and isolate the component from the circuit under test 5 February Meters 1

8 Schematic Symbols for Meters The analog voltmeter and ammeter must be connected to the circuit with proper polarity to avoid damaging the meter movement The ohmmeter may only be used on unenergized components 5 February Meters 15 Voltage 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 ammeter 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 scale 5 February Meters 16

9 A Voltmeter Connected to Measure Voltage 5 February Meters 17 Current 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 scale 5 February Meters 18

10 An Ammeter Connected to Measure Current 5 February Meters 19 Resistance 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 component 5 February Meters

11 Ohmmeter Connection to Measure Resistance 5 February Meters 1 Reading the Analog Meter

12 Example 1 Assume that the VOM shown is on the AC/DC 6 V scale. What is the reading? 5 February Meters 3 Example 1 Solution Assume that the VOM shown is on the AC/DC 6 V scale. What is the reading?.5 V Note that the reading is made on the 6 V scale and the user places the decimal. 1k 5 AC DC OHMS AC AMPS 5 1 dbm AC 1 DC dbm OHMS AC AMPS ANALOG MULTIMETER 5 February Meters

13 Example Assume that the VOM shown is on the AC AMPS 3 A scale. What is the reading? 5 February Meters 5 Example Solution Assume that the VOM shown is on the AC AMPS 3 A scale. What is the reading? 1.5 A Note that the reading is made on the 3 A AC scale and the user places the decimal place. 1k 5 AC DC OHMS AC AMPS 5 1 dbm AC 1 DC dbm OHMS AC AMPS ANALOG MULTIMETER 5 February Meters 6

14 Example 3 When you change resistance scales on a VOM, what must first be done before measuring a resistor? 5 February Meters 7 Example 3 Solution When 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. 5 February Meters 8

15 Example Assume that the VOM shown is on the Ω x1 scale. What is the reading? 5 February Meters 9 Problem Solution Assume that the VOM shown is on the Ω x1 scale. What is the reading? 3Ω Note that the reading is made on the Ω scale and the user multiplies the reading by 1. 5 February Meters 3