What is Current and How to Measure It: Full Guide

Measuring current is crucial for gauging the performance and safety of devices or circuits. This makes it a fundamental skill for anyone working in the field of electrical engineering. In this article, we will discuss some basic knowledge about currents and provide a guide on using the necessary tools to measure currents effectively. 

1. What is Current?

Current refers to the flow rate of electrons (also known as electrical charge) in a complete electrical circuit. It is measured in amperes (A) or simply amp for short, expressing the amount of electrons flowing past a single point in a circuit over time. For example, 1 ampere represents 1 coulomb of charge (6.24 x 10^18 electrons) past a specific point in a circuit within one second. 

In the Ohm’s Law equation V = I x R, current is also expressed as I for intensity, while V represents voltage (measured in volts) and R represents resistance (measured in ohms). This equation shows that the current flowing through a circuit is directly proportional to the voltage applied and inversely proportional to the resistance of the circuit.

To form a current, two essential conditions must be met:

1. Voltage Source: There must be a voltage source, such as a battery or generator, which creates an electric field, forcing the electrons to move through the conductor.
2. Closed Circuit: The circuit must form a continuous, unbroken loop. This means there must be a path for the electrons to flow from the voltage source, through the conductor, and back to the source. If the circuit is broken (e.g., by an open switch), the electrons cannot flow, and there will be no current.

Within the closed circuit, the flow direction of the electrons will determine whether the current is direct or alternating:

• Direct Current (DC) which is commonly produced by batteries or DC generators, flows in one direction only,  and it is mostly used in home appliances and other consumer devices. 
• Alternating Current (AC) changes direction periodically, flowing back and forth like a wave. It is more efficient for long-distance transmission, which is why it's the preferred choice for powering homes and most electrical grids.

By knowing which type of current you are dealing with, you can choose the optimal equipment settings later on when you are doing measurements.

2. How to Measure Current 

Measuring current involves using specialized instruments to quantify the flow of electrical charge through a circuit. The most common tools used for this task are digital multimeters (DMMs). DMMs are versatile instruments that can measure current, as well as voltage and resistance. By understanding how to use DMMs, you will be able to grasp the basics of current measurement with most equipment. 

Source: Freepik

Before beginning, carefully review your digital multimeter's user manual to understand its specific features and safety instructions. Then, you can follow our step-by-step guide to measure current with your digital multimeter:

1. De-energize Circuit: Ensure the circuit is powered off to prevent electrical shock or damage to the multimeter.

2. Connect Test Leads: Plug the appropriate test leads into the multimeter. The black lead typically connects to the "COM" (common) terminal, while the red lead is inserted into the "A" (ampere) terminal.

3. Clear Buffer: If your multimeter has a memory buffer, clear it to avoid interference from previous readings.

4. Select Current Mode: Turn the dial or press the appropriate button to select the "current" mode on the multimeter.

5. Choose Range: Select the current range that best suits your expected measurement. To prevent overloading, start with a higher range and then gradually decrease it.

6. Break the Circuit: Carefully disconnect the circuit at a suitable point.

7. Insert Multimeter: Connect the red and black leads to the exposed wires of the circuit. Ensure the multimeter is inserted in series so that the current flows through the DMM.

8. Activate Multimeter: Press the "trigger" or "read" button on the multimeter.

9. Observe Reading: Hold the leads in place for a few seconds and the current measurement will be displayed on the multimeter's screen after it stabilizes. 

10. Disconnect: Once you've completed your measurements, disconnect the multimeter from the circuit and power it back on. 

Using DMMs effectively lets you confidently measure current, ensuring precision and safety across your projects. Our featured DMMs include the Keithley DMM6500 and Siglent SDM3065X, each offering reliable performance for various measurement tasks.

3. Equipment Alternatives for Measuring Current

Digital multimeters pose limitations in certain situations. Thus, electrical engineers may consider the following equipment as alternatives:
 

• Oscilloscopes: These are essential for measuring and analyzing time-varying currents, especially alternating current (AC). On top of measuring the rate, they can also display the current waveform, providing valuable insights into its characteristics. Our featured products include the Tektronix MSO5B and Siglent SDS3000X HD, renowned for their high-resolution displays and advanced analysis features.
   
• Source Measure Unit (SMU): SMUs are recommended for more complex measurements and applications requiring higher precision. It combines the functionalities of a DMM, power supply, electronic load, current source, and pulse generator, making them suitable for various electronic testing tasks. The Keithley 2400 and Yokogawa GS610 are leading our selection, each recognized for delivering dependable performance across diverse testing scenarios.

If you are interested in how they work, you can check out the articles below to learn more about Source Measure units and Oscilloscopes:

➤ What is a Source Measure Unit(SMU): Features, Applications & More

➤ What is an Oscilloscope: Function, Usages, Types & More 

3. Precise Current Measurement Equipment at ESE 

As a trusted equipment supplier, ESE remains dedicated to providing top-quality products to meet your testing requirements, including easy-to-use Source Measure Units that combine various measurement functions to streamline your operations. Our commitment to excellence ensures that you receive the highest standard of support and service. For more information about our comprehensive product range or to place an order, please don't hesitate to contact us. Your satisfaction is always our priority.

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