21.4 DC Voltmeters and Ammeters
3 min read•june 18, 2024
DC and are essential tools for measuring electrical properties in circuits. These instruments allow us to quantify voltage and current, providing crucial data for understanding and troubleshooting electrical systems.
Proper use of voltmeters and ammeters requires understanding their connections, internal workings, and potential sources of error. By mastering these concepts, we can accurately measure and analyze DC circuits, laying the foundation for more advanced electrical studies.
DC Voltmeters
Voltmeter connections in circuits
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- Voltmeters measure (voltage) across a component
- Connect in with component ensures same voltage experienced
- components have the same across them
- Voltmeters designed with high
- Minimizes current drawn by voltmeter, preventing significant circuit operation impact
- Ideal voltmeter should draw no current to avoid altering measured voltage (, )
Galvanometer conversions for measurements
- is a sensitive instrument that detects and measures small electric currents
- Converting to voltmeter:
- Connect high-value resistor () in series with galvanometer
- Resistor limits current through galvanometer, allowing voltage measurement
- Resistor value determines voltmeter voltage range
- Converting galvanometer to :
- Connect low-value resistor () in parallel with galvanometer
- Shunt resistor diverts most current away from galvanometer, allowing higher current measurement without damage
- Shunt resistor value determines ammeter current range
Resistance calculations for voltmeter ranges
-
required to convert galvanometer to voltmeter with desired voltage range :
- is the current of galvanometer
- is the of galvanometer
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Series resistance limits current through galvanometer to value when desired voltage applied (50 μA, 1 mA)
DC Ammeters
Ammeter placement in diagrams
- Ammeter measures electric current flowing through a circuit
- Measure current in specific circuit branch by connecting ammeter in series with branch
- Ensures all current flowing through branch also flows through ammeter
- Ammeters designed with low internal resistance
- Minimizes voltage drop across ammeter, preventing significant circuit operation impact
- Ideal ammeter should have zero internal resistance to avoid altering measured current (, )
Uncertainty sources in DC measurements
- Instrument precision and accuracy
- Limited by smallest division on instrument scale and accuracy (±0.5%, ±1 digit)
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- Occurs when observer's eye not perpendicular to scale, leading to incorrect readings
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- Voltmeters: Drawing current from circuit can lower measured voltage
- Ammeters: Introducing resistance can reduce measured current
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- Nearby electronic devices or power lines can induce unwanted currents or voltages (AC power lines, transformers)
-
- Temperature changes can cause component and instrument drift from calibrated values (resistors, semiconductor devices)
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- Poor connections between instrument probes and circuit can introduce additional resistance, affecting measurements (corroded terminals, loose connections)
Measurement Techniques and Instrumentation
Analog vs. Digital Instruments
- Analog instruments use mechanical movements to display measurements
- Digital instruments provide numeric readouts, often with higher precision
- Both types require proper calibration for accurate measurements
Circuit Analysis and Electrical Components
- Understanding basic circuit theory aids in proper instrument use
- Knowledge of various (resistors, capacitors, inductors) essential for accurate measurements
Electrical Safety
- Always follow proper safety procedures when working with electrical circuits
- Use appropriate personal protective equipment and insulated tools
Electromagnetism in Measurement Devices
- Many measurement instruments rely on electromagnetic principles for operation
Key Terms to Review (40)
Ammeter: An ammeter is an electrical instrument used to measure the electric current flowing through a circuit. It is a crucial component in the study of DC voltmeters and ammeters, as it allows for the direct measurement of the current passing through a specific point in an electrical system.
Ammeters: Ammeters are instruments used to measure electric current in a circuit. They are connected in series with the component whose current is to be measured.
Analog meters: Analog meters are instruments used to measure electrical quantities such as voltage and current by using a needle and dial system. They operate based on the deflection of a pointer in response to an electric current or voltage.
Analog vs. Digital Instruments: Analog and digital instruments are two distinct approaches to measuring and displaying physical quantities. Analog instruments use continuous, variable signals to represent measurements, while digital instruments convert physical quantities into discrete numerical values for display. The choice between analog and digital instrumentation is an important consideration in various fields, including physics, engineering, and electronics.
Calibration: Calibration is the process of adjusting or standardizing a measurement instrument or system to provide a reliable and accurate output. It ensures that the measurements made by the instrument are consistent with known reference standards or values.
Circuit Analysis: Circuit analysis is the process of studying and understanding the behavior of electrical circuits, including the flow of current, the distribution of voltages, and the overall functionality of the circuit. It involves the application of fundamental principles and laws to analyze and solve problems related to the operation of various electrical components within a circuit.
Contact Resistance: Contact resistance is the electrical resistance that occurs at the interface between two conductive materials when they are in physical contact. It is an important consideration in the design and operation of electrical circuits and devices, as it can affect the overall performance and efficiency of the system.
Current sensitivity: Current sensitivity in a measuring instrument is the deflection per unit current. It indicates how effectively an instrument can detect small currents.
Current Shunt: A current shunt is an electrical device used in conjunction with an ammeter to measure large currents. It provides an alternative low-resistance path for a portion of the current being measured, allowing the ammeter to measure a smaller, more manageable current.
Digital meters: Digital meters are electronic devices used to measure electrical quantities such as voltage, current, and resistance. They display readings in a numerical form on an LCD or LED screen.
Digital Multimeter: A digital multimeter is an electronic measuring instrument that can display various electrical quantities, such as voltage, current, and resistance, in a digital format. It is a versatile tool used for troubleshooting and analyzing electrical circuits and components.
Electrical Components: Electrical components are the fundamental building blocks of electronic circuits, responsible for the generation, control, and manipulation of electrical signals and energy. These components are essential in the operation of various electrical devices, from simple household appliances to complex industrial machinery.
Electrical Safety: Electrical safety refers to the practices, precautions, and guidelines designed to protect individuals from the hazards associated with the use of electrical equipment and systems. It aims to minimize the risk of electric shock, fire, and other electrical-related injuries or incidents.
Electromagnetic Interference: Electromagnetic interference (EMI) is the disruption of the normal operation of an electronic device or system caused by the presence of electromagnetic radiation. This interference can affect the performance and reliability of various electronic components and systems, including those used in DC voltmeters and ammeters.
Full-scale deflection: Full-scale deflection is the maximum deflection of a measuring instrument's pointer or indicator, corresponding to the maximum current or voltage that the instrument can measure. It represents the upper limit of the instrument's range.
Full-Scale Deflection: Full-scale deflection refers to the maximum or full-range reading that can be displayed on the scale of a measuring instrument, such as a voltmeter or ammeter. It represents the upper limit of the instrument's measurement capability, beyond which the readings will be inaccurate or off-scale.
Galvanometer: A galvanometer is an instrument for detecting and measuring small electric currents by deflection of a needle. It operates on the principle that an electric current passing through a coil produces a magnetic field.
Galvanometer: A galvanometer is a sensitive instrument used to detect and measure small electric currents. It operates on the principle of the torque experienced by a current-carrying loop in a magnetic field, and is a crucial component in the functioning of voltmeters and ammeters.
Hall Effect Sensor: A Hall effect sensor is a transducer that varies its output voltage in response to changes in the magnetic field. It is commonly used to measure the strength of a magnetic field or to detect the presence of a magnetic object.
Internal resistance: Internal resistance is the opposition to the flow of current within a battery or power source, causing a voltage drop when current flows. It affects the terminal voltage and efficiency of the power source.
Internal Resistance: Internal resistance is the resistance within an electrical component or device that impedes the flow of electric current. It is an inherent property that arises from the physical and chemical characteristics of the component's materials and construction, and it affects the overall performance and behavior of the circuit.
Kirchhoff's Laws: Kirchhoff's Laws are a set of fundamental principles that describe the behavior of electric circuits. They provide a framework for understanding the flow of current and the distribution of voltage in both simple and complex electrical networks.
Loading Effect: The loading effect refers to the influence that a measuring device, such as a voltmeter or ammeter, has on the circuit being measured. This effect can alter the behavior of the circuit and impact the accuracy of the measurements taken.
Measurement Techniques: Measurement techniques refer to the methods and instruments used to quantify physical properties or parameters in a systematic and accurate manner. These techniques are essential for obtaining reliable data and making informed decisions in various scientific and engineering applications.
Multiplier Resistance: Multiplier resistance is a resistor or a combination of resistors used in electronic circuits, particularly in voltmeters and ammeters, to increase the range or sensitivity of the measuring instrument. It serves as a scaling factor, allowing the instrument to measure higher voltages or currents than its original design capacity.
Ohm's Law: Ohm's law is a fundamental principle in electrical engineering that describes the relationship between the voltage, current, and resistance in an electrical circuit. It states that the current flowing through a conductor is directly proportional to the voltage applied across it, and inversely proportional to the resistance of the conductor.
Parallax Error: Parallax error is a type of systematic error that occurs when the position of a measurement scale is not aligned with the pointer or indicator used to take the measurement. This discrepancy between the perceived and actual position of the measurement can lead to inaccurate readings, particularly in instruments such as voltmeters and ammeters.
Parallel: Parallel circuits are electrical circuits where components are connected across common points or junctions, providing multiple paths for current to flow. In a parallel configuration, the voltage across each component is the same.
Parallel: Parallel refers to a configuration or arrangement where components or elements are connected side-by-side, with each one operating independently but simultaneously. This concept is fundamental in understanding various electrical and electronic systems.
Potential difference: Potential difference is the work done to move a unit charge between two points in an electric field. It is measured in volts (V) and often referred to as voltage.
Potential Difference: Potential difference, also known as voltage, is the measure of the work required to move an electric charge between two points in an electric field. It represents the difference in electric potential energy between two locations, and is a fundamental concept in understanding the behavior of electric circuits and the flow of electric current.
Potentiometer: A potentiometer is an instrument for measuring the potential (voltage) in a circuit. It can also be used as a variable resistor to adjust voltage levels.
Potentiometer: A potentiometer is a three-terminal resistor used to measure or control voltage in an electrical circuit. It functions as an adjustable voltage divider, allowing for precise control of the output voltage within a specified range.
Sensitivity: Sensitivity refers to the ability of a measuring instrument to detect small changes in the quantity being measured. This is crucial for instruments to provide accurate readings, as higher sensitivity allows for better detection of variations in electrical signals, making it essential in precise measurements and analysis.
Series Resistance: Series resistance refers to the total resistance encountered by an electric current flowing through a circuit when the components are connected in a series configuration, where the current passes through each component sequentially.
Shunt resistance: Shunt resistance is a low-value resistor connected in parallel with an ammeter to allow most of the current to bypass the meter. It is used to extend the current range of the instrument while keeping the meter movement safe.
Shunt Resistance: Shunt resistance is a resistance connected in parallel with a device or component in an electrical circuit. It is used to control the amount of current flowing through the device or to measure the current flowing through it by diverting a portion of the current around the device.
Thermal Effects: Thermal effects refer to the changes in the properties and behavior of electrical components and circuits due to the influence of temperature. These effects can significantly impact the performance and reliability of electronic devices and systems.
Voltmeter: A voltmeter is an electronic instrument used to measure the potential difference, or voltage, between two points in an electrical or electronic circuit. It is a crucial tool for understanding and analyzing electrical systems across various contexts, including the study of electrical potential, electric hazards, and the operation of DC circuits.
Voltmeters: Voltmeters are instruments used to measure the electrical potential difference, or voltage, between two points in an electric circuit. They are connected in parallel with the component across which the voltage is to be measured.