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An ammeter is an electrical instrument used to measure the current flowing through a circuit. It is specifically designed to measure electric current, which is the rate of flow of electric charge, typically measured in units called amperes (amps).

Functionality and Design

Measurement Principle

  • Current Measurement: An ammeter is connected in series with the circuit or device under test. When current flows through the circuit, it passes through the ammeter, which measures the amount of current passing through it.
  • Scaling: Ammeters are calibrated to display the current in amperes (A), with the scale typically ranging from milliamps (mA) to several amps, depending on the application.

Types of Ammeters

  • Analog Ammeters: Traditional ammeters with a needle or pointer that moves across a calibrated scale to indicate the current.
  • Digital Ammeters: Modern ammeters that display the current reading digitally on a numerical display. They may offer additional features such as data logging and connectivity.

Internal Construction

  • Shunt Resistor: In analog ammeters, a shunt resistor is used to divert most of the current around the meter movement, allowing only a small, measurable amount of current to pass through the meter itself.
  • Galvanometer Mechanism: Analog ammeters often use a galvanometer mechanism to translate the current into a proportional mechanical movement of the needle.


Electrical Testing and Troubleshooting

  • Circuit Analysis: Ammeters are used by electricians, engineers, and technicians to measure current in circuits for analysis, troubleshooting, and maintenance.
  • Load Testing: They are essential for determining the current drawn by various electrical devices and components, ensuring they operate within safe limits.

Automotive and Battery Testing

  • Automotive Applications: In automotive diagnostics, ammeters are used to measure the charging and discharging currents of batteries and electrical systems.
  • Battery Testing: They help assess the condition of batteries by measuring the current during charging and discharging cycles.

Laboratory and Educational Use

  • Experimental Setup: Ammeters are used in physics and electronics laboratories to conduct experiments and verify theoretical principles related to electric current.
  • Educational Tools: They are valuable educational tools for teaching students about electrical circuits, Ohm’s law, and the behavior of electrical components.

Safety Considerations

Proper Usage

  • Current Rating: Ammeters should be selected based on their current rating to avoid damaging the instrument or causing inaccurate readings.
  • Series Connection: Care must be taken when connecting an ammeter in series with a circuit to ensure proper circuit operation and accurate current measurement.

Instrument Limitations

  • Overload Protection: Some ammeters are equipped with fuses or current-limiting protection to prevent damage from excessive currents.
  • Environmental Conditions: Operating ammeters within specified temperature and humidity ranges helps ensure accuracy and longevity.

An ammeter is a fundamental instrument in electrical engineering and testing, used to measure electric current accurately in circuits and devices. Whether in analog or digital form, ammeters play a crucial role in maintaining electrical systems, troubleshooting faults, and ensuring safe operation of electrical equipment in various applications ranging from industrial settings to educational laboratories. Understanding how to correctly use and interpret ammeter readings is essential for anyone involved in electrical maintenance, testing, or educational instruction related to electricity and electronics.


  • Recording Ammeter
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