Are you experiencing unexplained issues such as dropped connections, restarting gateways, or malfunctioning peripherals? In many cases, this is caused by electromagnetic interference (EMI) generated when switching relays. This article helps you quickly identify the problem and apply the correct solution.
Do you recognize this problem?
USB connections that unexpectedly disconnect.
HDMI connections that briefly drop out.
Audible interference on audio equipment.
PLCs behaving erratically or incorrectly.
Calculus gateways that reboot or temporarily lose their connection.
Cause at a glance
When relays are switched, especially with inductive or heavy loads such as heaters, motors, or contactors, high voltage spikes can occur. These spikes generate electromagnetic interference (EMI), which can disrupt other electronic equipment nearby. Because this interference depends on load type and switching moment, the problem may occur intermittently.
How to prevent EMI?
DC relays (12-24V)
Use relays with built-in suppression (such as a varistor), or install an external suppression component across the relay coil (A1 and A2). The suppression must be installed as close as possible to the relay coil to be effective.
A suitable low-voltage varistor is, for example, the Panasonic ERZV10D101. This item is for sale via this link: https://be.farnell.com/panasonic/erzv10d101/varistor-10mm-disc-100v/dp/1845438.
AC relays (230V)
Use a suitable suppression module for mains voltage. This module is installed across the relay coil and provides effective suppression of voltage spikes.
Alternatively, an X1/Y2-rated ceramic disc capacitor of 10nF with a minimum voltage rating of 300V can be used. This item is for sale via this link: https://be.farnell.com/vishay/vy2103m63y5ug6tv7/cap-0-01-f-20/dp/2860170.
Important!
Suppression components have a limited lifetime, just like the relays themselves. It is recommended to replace them together when a relay is replaced.
Grounding the 12-24V power supply
In some cases, connecting the GND or V- of a 12-24V power supply to earth ground can help reduce interference that propagates through conductors.
Attention!
In temporary installations or installations with unreliable grounding, this may actually increase interference or even cause damage. Always evaluate grounding carefully.
Basic rules for using a Calculus gateway
Never route USB or data cables close to relays or switch cabinets.
Maintain a minimum distance of 10 cm between relays and Calculus gateways.
Route power supplies and signals separately for each device and avoid shared conductors.
Why suppression is necessary
Relays and contactors can generate electromagnetic interference when switching. This interference can affect nearby devices, especially when multiple relays or heavy loads are switched. Suppression limits these effects and improves the overall reliability of the installation.