EMI (Electromagnetic Interference)
EMI is unwanted electromagnetic energy disturbing the operation of a device. EMC is a design goal; EMI is what happens when that goal is not met. On an industrial site the main sources are switching power circuits, motor drivers, welding arcs and contactor sparking.
An EMI event has three components, and you can intervene at any one of them:
- Source: the circuit generating the noise. Slowing the switching rate or adding a suppression component works here.
- Coupling path: the route the noise travels. Cable separation, shielding, ferrites and filters act on this component.
- Victim: the affected circuit. It can be an RF receiver, an analogue sensor input or a microcontroller.
In the field the most productive intervention is usually the coupling path, because changing the source is often not possible. Routing power and signal cables separately, crossing them at right angles, terminating the shield at a single point and moving the receiver antenna away from the noise source all give measurable gains. With wireless remote controls the symptom is typical: range is normal while the machine is stopped and drops once the motor or driver runs.
Context where this term is used: 433 MHz or 2.4 GHz?