Physics
Voltmeter
A voltmeter is an instrument used to measure the voltage or potential difference between two points in an electrical circuit. It typically consists of a sensitive galvanometer connected in parallel with a high resistance, allowing it to measure voltage without significantly affecting the circuit. Voltmeters are essential tools for analyzing and troubleshooting electrical systems.
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8 Key excerpts on "Voltmeter"
eBook - PDFElectrical Principles & Practice NQF4 SB
TVET FIRST
- Jowaheer Consulting and Technologies(Author)
- 2014(Publication Date)
- Macmillan(Publisher)
It is therefore important to know how to connect them in circuits, as each meter has its own limitations and they differ in construction as you have learnt in Levels 2 and 3. In this unit, you will investigate how to connect meters correctly in circuits. Voltmeters A Voltmeter is an instrument that is used to measure the potential difference or voltage between two points in a circuit. Connect a Voltmeter in parallel across the load. You can make the connection across the entire circuit, across a section of the circuit or across a component in the circuit. 31 Module 2: Measuring instruments Note that a Voltmeter must have a high resistance in order to prevent a current flowing through it. Figure 2.1 shows how to connect a Voltmeter in a circuit to measure the voltage. Ammeters An ammeter is an instrument that is used to measure the value of current in an electrical circuit. Connect an ammeter in series with the circuit so that it can read the entire current that flows through the circuit. Note that, in contrast to a Voltmeter, an ammeter has a very low resistance. To connect an ammeter, open the circuit and connect the ammeter as shown in Figure 2.2. Ohmmeters An ohmmeter is an instrument that is used to measure electrical resistance. Connect an ohmmeter in parallel in a circuit. When you measure resistance, make sure that the circuit power is off and that one of the terminals of the device is removed from the circuit. Figure 2.3 shows how to connect an ohmmeter in a circuit. ohmmeter resistor R x = unknown value of resistor Figure 2.3: Connecting an ohmmeter in a circuit Wattmeters A wattmeter is an instrument that measures DC or AC power in a circuit as shown in Figure 2.4. There are two types of wattmeters: electrodynamic wattmeters and dynamometers. Figure 2.5 shows the typical connections of a wattmeter used for measuring the power supplied to a load.
- John G. Webster(Author)
- 2003(Publication Date)
- CRC Press(Publisher)
1 -1 0-8493-1733-9/04/$0.00+$1.50 © 2004 by CRC Press LLC 1 Voltage Measurement 1.1 Meter Voltage Measurement .............................................. 1 -1 Electromechanical Voltmeters • Electromagnetic Voltmeters • Electrodynamic Voltmeters • Electrostatic Voltmeters • Electronic Voltmeters • Analog Voltmeters • Digital Voltmeters 1.2 Oscilloscope Voltage Measurement ................................. 1 -21 The Oscilloscope Block Diagram • The Oscilloscope as a Voltage Measurement Instrument • Analog or Digital • Voltage Measurements • Understanding the Specifications • Triggering • Conclusion • Selecting the Oscilloscope 1.3 Inductive and Capacitive Voltage Measurement ............ 1 -40 Capacitive Sensors • Inductive Sensors • Other Methods 1.1 Meter Voltage Measurement Alessandro Ferrero Instruments for the measurement of electric voltage are called Voltmeters . Correct insertion of a Voltmeter requires the connection of its terminals to the points of an electric circuit across which the voltage has to be measured, as shown in Figure 1.1. To a first approximation, the electric equivalent circuit of a Voltmeter can be represented by a resistive impedance Z v (or a pure resistance R v for dc Voltmeters). This means that any Voltmeter, once connected to an electric circuit, draws a current I v given by: (1.1) where U is the measured voltage. The higher the value of the internal impedance, the higher the quality of the Voltmeter, since it does not significantly modify the status of the electric circuit under test. Different operating principles are used to measure an electric voltage. The mechanical interaction between currents, between a current and a magnetic field, or between electrified conductors was widely adopted in the past to generate a mechanical torque proportional to the voltage or the squared voltage to be measured.
eBook - PDFElectricity and Electronics for Renewable Energy Technology
An Introduction
- Ahmad Hemami(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
Voltage, Current, and Power 87 turn to left in an analog device.) In some ammeters (not multimeters) with a needle the zero point is in the middle and the motion of the needle indi-cates both positive and negative readings. This is helpful for the circuits in which current can be either positive or negative. 5.6 Measuring Electric Voltage Because voltage is the potential difference between two points, to mea-sure voltage, the two leads of a Voltmeter must be connected to those points. Pay attention for measuring voltage; you should not open the cir-cuit. Whereas for measuring current, one must open the circuit. In Figure 5.3 we need to measure the voltage across the load. Thus, the Voltmeter is connected at points A and B so that the load is between points A and B (Figure 5.4). The measured value is the voltage applied to the load. A Voltmeter, in fact, measures the voltage difference between two points. Note that, whereas in a single (one loop) circuit there is only one cur-rent, there are various voltages depending on the number of components in the circuit and where the measurement is made. For instance, in Figure 5.5 there is a 100 Ω load and two 0.5 Ω wires connecting the load to the 120 V power supply. We may measure the voltage between each pair of points A, B, C, D, and E; for example, A-B, A-D, B-C, B-E, and so on. The measurement across the source shows the source voltage. Note that in Voltmeter: Electrical instrument to measure electric voltage. R Load = 100 Ω 120 V 0.5 Ω A Insert the meter in the circuit 0.5 Ω Figure 5.2 Step 2 for measuring the current in a circuit. V 0.5 Ω 120 V A B 0.5 Ω Figure 5.3 Use a Voltmeter to measure voltage between two points. 88 Electricity and Electronics for Renewable Energy Technology Figure 5.5 all the points A to E are selected at a graphically suitable point in the line connecting two elements together. Any other point on each line denotes the same point of the circuit.
- Russell Smith(Author)
- 2018(Publication Date)
- Cengage Learning EMEA(Publisher)
You can also detect many electric circuit problems with a clamp-on ammeter, and it is the easiest, quickest way to tell if a load or circuit is energized. The ammeter can be purchased with other meters built into it. For example, a single clamp-on ammeter can be purchased that will read amperage, voltage, and resistance. 4.3 VoltmeterS The Voltmeter is used to measure the amount of electromotive force avail-able to a circuit or load. This is an important factor for heating, cooling, and refrigeration technicians because a wide range of voltages are used in this country. Voltmeters range from simple to complex instruments containing many scales. The sim-plest Voltmeter available is a small, inexpensive one capable of distinguishing only among 120, 240, 480, and 600 volts ( Figure 4.17 ). Several manufacturers build simple Voltmeters that can read only voltages, but these are becoming increasingly difficult to obtain. More common is the volt-ohm meter, which reads both volt-age and resistance. These are available in many forms, and service technicians should follow the instructions for the particular model being used. The common volt-ohm meter has three voltage scales and several voltage ranges. Some meters also have a high-voltage jack. Figure 4.18 shows a common type of analog volt-ohm meter. Figure 4.19 shows a digital volt-ohm meter. The Voltmeter was designed much like the ammeter, but a resistor is added to the circuit to prevent a direct short and allow electrons to flow in the meter. The Voltmeter uses two leads that are connected to jacks that lead to the internal wiring. To obtain a reading, the two leads must touch or be connected to the conductors supplying the load or to the circuit that transfers the electromotive Simple Voltmeter © Cengage ® FIGURE 4.17 Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.
eBook - PDF- John Linsley Hood(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
Digital instruments can give a much greater degree of precision in reading (usually limited to +/-1 in the least significant digit), particularly in measurements of circuit resistance, and are particularly useful in determining the differential potential existing between non-zero points, such as across the load resistor (points 'x' and 'y') of the simple amplifier circuit shown in Figure 17.1. However, they do not usually approach the ideal zero voltage drop condition in current meas-urement applications as closely as, for example, an electronic analogue meter, and they are virtually use-less for measurements of changing voltage or current levels, which makes them very awkward to use as a peak or a null detector during circuit adjustments. There are, indeed, some digital Voltmeters (DVMs) which have a ten or fifteen segment 'bar-graph' dis-play, in addition to the digital read-out, but these offer nowhere near the delicacy of adjustment possible with even a cheap analogue meter. W / o Figure 17.1 Most direct reading analogue displays are based on the use of a 'moving coil' indicating instrument, some-times called a d'Arsonville movement, after its inven-tor. The construction of these is shown, schematically, in Figure 17.2. In this, a coil of wire, wound on a thin rectangular former, is suspended in the gap between a pair of magnetic pole-pieces, and pivoted so that it is Test and measurement equipment 289 free to swing about its axis. A pointer is attached to this movable coil, and the whole movement is caused to return to some predetermined zero position by means of a pair of spiral wound springs. These are mounted in opposition, so that very little torque is required to cause the movement to swing about its axis. The displacement of the meter movement away from its zero position is due to the interaction of the magnetic field due to the permanent magnet and that due to passage of current through the coil to which the external meter circuit is connected.
eBook - ePub- Dale Patrick, Stephen Fardo(Authors)
- 1999(Publication Date)
- Newnes(Publisher)
Unit 2Measuring Voltage, Current, and Resistance
Another important activity in the study of electronics is measurement. Measurements are made in many types of electronic circuits. The proper ways of measuring resistance, voltage, and current should be learned. These are the three most common electric measurements.UNIT OBJECTIVES Upon completing this unit, you will be able to do the following:1. Connect an ammeter in a circuit and measure current.2. Demonstrate how the Voltmeter, ammeter, and ohmmeter are connected to a circuit.3. Measure current, voltage, and resistance of basic electronic circuits.4. Compare calculated and measured values of a circuit.5. Demonstrate safety while making electric measurements.6. Demonstrate proper, safe use of an ohmmeter to measure resistance.Important Terms
Before reading this unit, review the following terms for a basic understanding of terms associated with electronic measurement.Ammeter A meter used to measure current (amperes).Continuity check A test to see whether a circuit is an open or closed path.Multimeter A meter used to measure two or more electric quantities, such as a volt-ohm-milliammeter (VOM), which measures voltage, resistance, and current, or a digital Voltmeter (DVM).Multirange meter A meter that has two or more ranges to measure an electric quantity.Ohmmeter A meter used to measure resistance (ohms).Polarity The direction of an electric potential (– or +) or a magnetic charge (north or south).Schematic A diagram used to show how the components of electric circuits are wired together.Voltmeter A meter used to measure voltage.Volt-ohm-milliammeter (VOM) A multifunction, multirange meter that usually is designed to measure voltage, current, and resistance; also called a multimeter.Measuring Resistance
Many important electric tests may be made by means of measuring resistance. Resistance is opposition to the flow of current in an electric circuit. The current that flows in a circuit depends on the amount of resistance in that circuit. You should learn to measure resistance in an electric circuit by using a meter.
eBook - PDF- Stephen Herman(Author)
- 2016(Publication Date)
- Cengage Learning EMEA(Publisher)
21 MEASURING INSTRUMENTS Unit 3 Objectives After studying this unit, the student should be able to: ❯❯ Discuss the operation of a digital multimeter. ❯❯ Measure voltages with a digital multimeter. ❯❯ Measure resistance with a digital multimeter. ❯❯ Determine the amount of current flow in a circuit. ❯❯ Discuss the operation of an oscilloscope. ❯❯ Discuss various oscilloscope controls. ❯❯ Connect an oscilloscope in a circuit. ❯❯ Interpret wave forms produced on the display of an oscilloscope. The ability to measure values of voltage, current, and resistance in an electronic circuit is paramount for an industrial electrician. The two most common instruments to perform this job are the multimeter and the oscilloscope. Multimeters can be divided into two basic types: analog and digital. Analog meters are characterized by the fact that they contain a meter movement with a moving pointer, Figure 3-1. Although meters of this type have been used by electricians for many years, they are generally not the best choice for troubleshooting electronic circuits. Most analog Voltmeters work on the principle of inserting resistance in series with the meter movement to affect a change in the full scale value of the meter, Figure 3-2. A common resistance value for a DC Voltmeter is 20,000 ohms per volt. This means that if the meter is set for a full scale value of 15 volts, it will have an internal resistance of 300 k V (20,000 3 15). If the meter is set on the 15-volt range, it will require a current of 50 m A (microamperes) to operate the meter movement (15V/300 k V ). If this meter is used to measure the voltage in a circuit that contains low resistance and a high current capacity, there is no problem. The amount of current needed to operate the meter movement is not sufficient to disrupt the circuit. Now assume that this meter is to be used to measure the voltage drop across a 120-k V resistor in a circuit that contains a current flow of 100 m A.
eBook - PDF- Michael Brumbach(Author)
- 2016(Publication Date)
- Cengage Learning EMEA(Publisher)
When preparing to measure voltage or current, you should verify the operation of your meter on a known, good source of voltage or current. You should test the meter on the function and range that you expect to use. Many a technician has been injured or killed as a result of trusting a faulty meter. Imagine that you are preparing to work on a circuit. You need to know if the circuit is energized or not, so you connect your meter into the circuit to measure voltage, and you read 0 V. You assume that the circuit is de-energized and begin to work. Upon coming into contact with the circuit, you receive an electrical shock! How can this happen if the meter indicates 0 V? Your meter is defective and cannot measure voltage. THE DIGITAL MULTIMETER The most common multimeter in use today is the digital multimeter (Figure 4–1). The digital multi-meter is so named because the measured value is displayed in a digital readout. This is an improve-ment over the older analog style of display in which you had to match a moving indicator (vane or nee-dle) to a fixed scale. These analog indicators were prone to inaccuracies and difficulties in obtain-ing correct measurements. The digital display has made using a multimeter much easier. The digital multimeter, or DMM, may be bench or panel mounted, or more commonly in maintenance, handheld. The operation of these DMMs is essentially the same. The major differ-ences are in their functions and accuracies. Most bench or panel-type DMMs have more ranges, FIGURE 4–1 Digital multimeter. Copyright 2017 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
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