Electromagnetic interference, commonly called EMI, is a form of emission from electromagnetic units that causes some disturbance in other electrical items. Every device that works with rapidly changing electrical currents must give off this kind of emissions. These types of currents include microwave, direct currents, alternating currents and radio frequencies.
The interference, in this case, comes in the form of data degradation such as on a hard drive, obstructing the transfer of data through media or causing the electrical equipment to lose all data it stores or has been transferring.
How does Interference Happen?
Electromagnetic interference happens in two ways. It may occur if the victim device comes into contact with the device that is emitting the EMI. This method is called conduction and the source is called a conductor. This type of interference is called conducted EMI.
Interference can happen without physical contact between the devices involved through radiation. This form of interference is called radiated EMI. This form of interference is common with high-speed cabling and high voltage power lines.
Almost all electrical devices emit some form of EMI. If they are allowed to run without regulation, there would be chaos as many devices would not work as they should. For this reason, an organisation called International Special Committee on Radio Interference (CISPR) was created by the International Electrotechnical Commission. This organisation provides guidelines for the measurement, setting limits and offering ways to deal with EMI. The methods discussed below on managing EMI are derived from such regulations.
How to Deal with EMI
Grounding the Electrical System
Earthing is the first method of dealing with electromagnetic interference. It is done to the ground or a water pipe. The Outlet ground acts as an electrical drain where the charge in the EMI flows out of the electrical system. Earthing works on the principle that electricity flows through the path with the least resistance. This means that it will readily move through a heavy and thicker wire, leading to the ground rather than the weak electronic circuits of most of the electronic devices. Always use a three-plug cable for your connections.
If you are working with surface mount equipment, you may make use the surface mount device grounding contacts for quality SMD grounding. There is a choice of soft FR SMD grounding and high temp SMD grounding contacts. All of these SMD contacts come with a metallised outer covering and work well with automatic processing.
Go for Quality Cables
The quality of cables has a bearing towards the potential noise. When it comes to the quality, look at flex ratings, the gauge of the wire and the material that makes the outer casing. You also need to check at the cable’s flex ratings, shielding and terminations. If you go for devices that are metal-encased or high-power equipment, go for a three-flex cable for your electrical installations. Additionally, cables sheathed with solid plastic are good high-power conductors.
Separate Motor Signal and Power Cables
Route your power cables from signal cables. The cables should always run in separate conduits. If not, there should be a distance of at least four inches between them if each has lower than 20 amps current and 8 inches for cables that transfer more than 80 amps. Where you use a separate power filter, ensure that you maintain leads that are entering and leaving your power cabinet. In this case, the filter should be as close enough to the incoming lines as possible.
In case where you are using internal power filters, there should be at least four inches of space between your in-power and the motor leads. Where the motor leads and input power cross, ensure that they cross at right angles.
Make Use of Differential Inputs When Working with Analogue Signals
It is easier to deal with electromagnetic noise when working with analogue signals by installing differential inputs. The correct connection to the differential input involves connecting the signal output to the positive line differential input and the grounding of the device to the negative differential input. You should always go for shielded lines for your signal and a twisted pair to connect to the inputs. Twisted pairs equalize the effect of EMI on each of the wires and reduce errors based on it.
Use of Shields and Gaskets
Shielding is also a perfect way to protect your devices from offending EMI from other devices that may be causing problems especially if there is nothing much you can do to get lower the EMI. High-quality shielding gaskets and other shields help suppress EMI interference and increase immunity for your devices. They also isolate offending circuits shielding, filter and grounding and desensitise sensitive equipment from circuits that are susceptible to EMI interference. You can try solutions such as vent panels, knitted gaskets and wire mesh and metallised fabrics.
If you are working in an environment with high radio and microwave interference, you can go for products that absorb the currents. There are a number of solutions that solve your EMI problems by absorption. These include hybrid absorbers, microwave absorbing foams and customised magnetic and microwave absorbers. If none of these works for your equipment, you may consider cast, machined or moulded silicone or epoxy coatings. The choice of films and foams to use depends on the expected amount of interference, the sensitivity of your instruments and the environment in which your device is working. Ensure that your choice meets the minimum compliance requirements for your industry.
One of the global leaders in solving electromagnetic interference is Laird Technologies who provide stat of the art solutions across the world. The Official recognised distributer for the UK and Ireland is Techni3 who offer a comprehensive back up and after sales service, with knowledgeable engineers on hand to advice customers on the best design solutions and components to reduce electromagnetic interference.
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