Relay is the name for a switch that is operated electro-mechanically or electronically. Their main task is to make and break connections to control the flow of current in electrical circuits. They’re used for various purposes ranging from validating semiconductors to interfacing low power computers or microcontrollers with high power machinery.
There are two main types of relays. Electromechanical Relays use an inductor to mechanically operate the arm of the switch while Solid State Relays (SSR) have no moving parts but instead use the electrical and optical properties of semiconductors to perform their switching functions. At ACCES I/O we use Field Effect Transistor (FET) switches for non-mechanical solutions as they have faster switching speeds and smaller form factors than traditional SSRs.
In order to choose the right relay for your application it is useful to first take note of the key differences between main types of relays.
In Electromechanical Relays (commonly just relays) the connection is controlled by an arm that opens and closes as a response to the magnetic field induced in the coil on the other side. The mechanical robustness of this connection allows it to operate in harsh conditions and to support a wide range of signals, but that’s also what makes this connection slower (5-15ms) and bulkier. Another important occurrence in Electromechanical Relays resulting from its construction is so called contact bounce that causes a noise after switching the relay position to closed but it can be efficiently cushioned by using a debouncing filter.
FETs (often called high side or low side switches) due to their non-mechanical nature offer zero contact bounce and are much faster (0.5-1ms) and smaller. The common problem with them is that they require a minimum load to work and they can switch only DC signals. They’re recommended whenever faster and more frequent switching is required and are a perfect solution for low noise applications like precise measurements.
For more information about different variants of FETs and Electromechanical Relays and guidance on how to choose the right relay for your application, click here.