In electronics and instrumentation, one of the most common and frustrating issues is EMI, which stands for Electromagnetic Interference.
It can cause equipment to behave strangely, give incorrect readings, or even stop working completely.
In this article, we will explain what EMI is, where it comes from, how it affects your instruments, and how to protect your systems from EMI
EMI (Electromagnetic Interference) is unwanted noise or signals that interfere with the normal operation of electronic devices.
It is like someone shouting in your ear while you are trying to listen to soft music, the loud noise (EMI) disturbs the signal you want to hear.
EMI is caused by electromagnetic fields that are produced by other electrical or electronic equipment. These fields can interfere with signals being transmitted or received by nearby devices, especially if those signals are weak or sensitive, such as sensor outputs.
Main Types of Electromagnetic Interference
There are three main types of EMI
1. Conducted EMI
This type of interference travels through wires or cables.
Conducted EMI occurs when electrical noise travels through a physical connection, such as wires or power lines, from the source to the affected device. It commonly originates from equipment like large motors or power supplies
2. Radiated EMI
This type of interference travels through the air in the form of electromagnetic waves.
For example, walkie-talkies or mobile phones can send out strong radio waves that disturb nearby sensitive instruments
3. Coupled EMI
It occurs when the source of interference and the affected device are close to each other but not directly connected by wires.
This type of interference is passed through either magnetic fields (inductive coupling) or electric fields (capacitive coupling).
There are two types of coupled EMIs
- Inductive (magnetically coupled) EMI happens when the magnetic field from one wire or device creates an unwanted current in another nearby wire. A common example is when a power cable runs close to an audio cable, causing a humming noise in the audio system.
- Capacitive (electrically coupled) EMI occurs when two wires or conductors are very close and act like a capacitor, allowing unwanted signals to pass between them. This usually happens on circuit boards or where many wires are packed tightly and run over long distances.
Common Sources of Electromagnetic Interference
EMI can come from many sources in an industrial or laboratory environment. Some common sources include:
- Electric motors and pumps
- Variable frequency drives (VFDs)
- Relay contacts and switching circuits
- Welding machines
- Microwave ovens
- Power lines or transformers
- Mobile phones and radio transmitters
Even small electronic devices can cause EMI if they are poorly designed or not properly shielded
How to Protect Electronic Instruments from EMI?
Now we know how dangerous EMI can be, here are some simple ways to reduce or prevent it:
1. Use Shielded Cables
Use shielded signal cables, especially for low-level analog signals. The shielding helps to block EMI from entering the cable. Make sure the shield is grounded correctly – usually at one end only.
2. Proper Grounding
Good grounding is essential. Ground loops can act like antennas and pick up EMI. All instruments should be properly grounded to avoid floating voltages and noise pickup.
3. Keep Power and Signal Cables Separate
Never run power cables and signal cables in the same tray or conduit. EMI from power cables (especially those going to motors or VFDs) can easily enter signal wires if they are placed together.
4. Use Ferrite Beads or Filters
Ferrite beads or line filters can be installed on power or signal cables to block high-frequency noise.
5. Enclosures and Shielding
Always use metal enclosures or EMI-proof housings for sensitive devices. These can block radiated EMI.
6. Twisted Pair Wires
Use twisted-pair cables for analog and digital signals. Twisting helps cancel out noise from nearby sources.
7. Use Opto-Isolators or Signal Isolators
These devices help protect signals by isolating the input and output sides electrically. This prevents ground loops and reduces the chance of EMI.
Tips for Instrument Technicians
- Always use proper cable routing during installation.
- Use differential inputs on controllers whenever possible to reduce noise.
- Check for loose connections, as they can increase noise pickup.
- During maintenance, inspect for damaged cable insulation or ungrounded shields.
- When working near VFDs, welders, or large motors, expect EMI and plan your installation accordingly.
Final Thoughts
Electromagnetic Interference (EMI) is a hidden problem that can seriously affect the performance of your electronic instruments. It comes from many sources from motors to mobile phones and can cause incorrect readings, communication failures, or even shutdowns.
The good news is that EMI can be controlled using smart design, good installation practices & proper shielding.
As students and future professionals in instrumentation and electronics, it is important to understand EMI and how to deal with it, so your systems work reliably and accurately in the real world.
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