How to Test an Inductor with a Multimeter: A Step-by-Step Guide

Inductors are fundamental components in electronic circuits, crucial in filtering, energy storage, and inductance. Testing an inductor is essential to ensure it functions correctly, and a multimeter is one of the most effective tools for this task.

This article will guide you through testing an inductor with a multimeter, helping you verify its condition and performance.

How to Test an Inductor with a Multimeter

1. What You Need

Before you begin, gather the following tools and materials:

  • Multimeter
  • Inductor

2. Set Up Your Multimeter

Setting up your multimeter correctly is crucial for obtaining accurate readings when testing an inductor. Here’s a detailed guide on how to prepare your multimeter for the task:

Selecting the Appropriate Mode

  1. Turn On the Multimeter: Press the power button to turn on your multimeter.
  2. Select Resistance Mode (Ω): Locate the dial or button that switches between different measurement modes. Turn the dial to the resistance measurement setting, often marked by the Ω symbol.

Preparing the Probes

  1. Check the Probes: Ensure that the probes (also known as test leads) are in good condition. Look for any signs of wear, damage, or loose connections. Faulty probes can lead to inaccurate readings.
  2. Connect the Probes: Insert the probes into the correct jacks on the multimeter. Typically, the black probe goes into the common (COM) jack, and the red probe goes into the jack labeled for resistance or inductance (Ω or L).

Choosing the Correct Range

  1. Automatic Range Selection: Many modern digital multimeters have an auto-ranging feature, which automatically selects the appropriate measurement range. This feature simplifies the setup process and ensures accurate readings.
  2. Manual Range Selection: If your multimeter requires manual range selection, choose a range higher than the expected inductor’s resistance. For example, if you expect the inductor to have a few ohms resistance, set the range to the next higher value, such as 20 ohms.

3. Identify the Inductor Terminals

Identifying the terminals of an inductor is a crucial step before performing any measurements. Proper identification ensures accurate testing and prevents potential damage to the inductor and the multimeter.

inductor

Here’s a more detailed approach to this step:

Understanding Inductor Basics

Inductors are passive components that store energy in a magnetic field when an electrical current flows through them. They are usually defined by their inductance value, which is measured in henries (H).

Inductors come in various shapes and sizes, including through-hole, surface-mount, and toroidal designs. Despite these variations, all inductors have two terminals.

Types of Inductors and Their Terminals

  1. Axial Inductors: These inductors resemble resistors and have leads extending from each end. The leads are the terminals you need to connect to the multimeter probes.
  2. Radial Inductors: These inductors have leads protruding from the same side, usually designed to be mounted vertically on a circuit board. The protruding leads are the terminals.
  3. Surface-Mount Inductors: These are small, compact inductors used in surface-mount technology (SMT). They have flat contacts or pads on the bottom that serve as terminals.
  4. Toroidal Inductors: These inductors are wound on a doughnut-shaped core. The wires extending from the coil are the terminals.

Steps to Identify the Terminals

  1. Visual Inspection: Begin by visually inspecting the inductor to locate the terminals. This step is straightforward for axial and radial inductors with easily visible leads. For surface-mount and toroidal inductors, look for the contact pads or wires extending from the coil.
  2. Consult the Datasheet: The inductor’s datasheet provides detailed information about the terminal locations and characteristics. The datasheet often provides diagrams and specifications clarifying which parts of the inductor are terminals.
  3. Labeling and Markings: Some inductors, especially those used in industrial or professional applications, may have markings or labels indicating the terminals. These markings can help ensure you connect the probes correctly.
  4. Circuit Context: If the inductor is part of a larger circuit, trace the circuit board to identify where the inductor connects. The solder points or contact pads on the PCB where the inductor is mounted will indicate the terminals.
  5. Polarity Considerations: While most inductors do not have polarity (they can be connected in either direction), some specialized inductors, such as those with integrated diodes or multiple windings, might have polarity markings. Ensure you note any such markings to avoid incorrect connections.

Practical Tips

  • Use Appropriate Probes: Fine-point probes are used for small or surface-mount inductors to ensure good contact with the terminals.
  • Clean the Terminals: Ensure the inductor terminals are clean and free from oxidation or solder flux residues. This can affect the accuracy of your measurements.
  • Handle with Care: Inductors, especially surface-mount types, can be delicate. Handle them carefully to avoid damaging the terminals or the component itself.

4. Measure the Resistance

  1. Connect the Probes: Connect the multimeter probes to the inductor terminals. Polarity is not important when measuring resistance.
  2. Read the Resistance: Observe the multimeter reading. A good inductor should have low resistance, typically close to zero ohms. High resistance indicates a problem, such as a broken winding or poor connections.

5. Analyze the Results

  • Low Resistance and Correct Inductance: The inductor is likely in good condition if the resistance is low.
  • High Resistance: High resistance suggests a damaged inductor with possible broken windings or poor connections.

6. Tips for Accurate Testing

  • Use Quality Probes: Ensure your multimeter probes are in good condition to avoid false readings.
  • Stable Environment: Perform tests in a stable environment, free from significant temperature fluctuations or electromagnetic interference.
  • Reference Values: Always compare your readings with the inductor’s datasheet or specifications to make an informed assessment.

How Can the Physical Design of an Inductor Affect Its Performance in a Circuit?

The physical design of an inductor affects its performance in several ways, including its inductance value, quality factor (Q factor), and resistance. Here are some key aspects to consider:

1. Core Material

The core material of an inductor plays a vital role in determining its inductance and efficiency. Common core materials include:

  • Air Core: These inductors use air as their core material. They are commonly employed in high-frequency applications because they can avoid core saturation and maintain low losses. However, air core inductors typically have lower inductance values compared to those with ferromagnetic cores.
  • Ferrite Core: Ferrite cores are made from a type of ceramic material that enhances the inductance by concentrating the magnetic field. Ferrite core inductors are commonly used in power applications and for EMI filtering due to their high inductance and ability to handle significant current.
  • Iron Core: Iron core inductors provide high inductance and are used in applications requiring substantial energy storage. However, they can suffer from core losses at high frequencies.

2. Winding Configuration

The way the wire is wound around the core also impacts the inductor’s performance:

  • Single-Layer Winding: This configuration involves a single layer of wire wrapped around the core. It is simple and effective for small inductors but can limit the inductance value and current-handling capability.
  • Multi-Layer Winding: Multiple layers of wire increase the inductance and current-handling capability. However, multi-layer windings can introduce parasitic capacitance, affecting performance at high frequencies.
  • Toroidal Winding: Toroidal inductors have wire wound around a doughnut-shaped core. This design minimizes electromagnetic interference (EMI) because the magnetic field is contained within the core. Toroidal inductors are highly efficient and suitable for high-frequency applications.
inductor in PCB

3. Size and Shape

The physical dimensions of an inductor influence its inductance and resistance:

  • Larger Inductors: Generally provide higher inductance and can handle more current due to larger wire gauges and better heat dissipation. They are often used in power applications.
  • Smaller Inductors: Suitable for high-frequency applications and compact designs, but they might have higher resistance and lower current-handling capability due to thinner wires and limited space for heat dissipation.

4. Shielding

Some inductors are designed with shielding to reduce electromagnetic interference. Shielded inductors are essential in sensitive electronic applications where EMI can affect circuit performance.

Conclusion

Testing an inductor with a multimeter is straightforward and can help you ensure your electronic circuits function correctly. Following the steps outlined in this guide, you can quickly diagnose and verify the condition of inductors, ensuring they meet their specified performance parameters.

Regular testing and maintenance of inductors can save time and resources for your electronic projects, leading to more reliable and efficient circuits.

Frequently Asked Questions

How can I tell if my inductor is damaged?

Measure its resistance and inductance with a multimeter. If the resistance is high or the inductance significantly differs from the specified value, the inductor is likely damaged. A good inductor should have low resistance and an inductance close to its rated value.

Can I test an inductor while it’s still in the circuit?

It’s best to test an inductor out of the circuit to avoid interference from other components. Disconnect it from the circuit for accurate measurements. In-circuit testing can give misleading results due to parallel pathways.

What should I do if my multimeter doesn’t have an inductance setting?

You can still test the inductor’s resistance with the ohms setting. Low resistance suggests the inductor is likely good, while high resistance indicates potential issues. For precise inductance measurements, consider using an LCR meter.

Alex Klein Author

Author

Alex Klein is an electrical engineer with more than 15 years of expertise. He is the host of the Electro University YouTube channel, which has thousands of subscribers.