Relays, Timers & Counters
Contactors are electrical control devices used to switch a circuit on or off. They are considered to be a special type of relay that are used in higher power applications. These heavy-duty relays allow lower currents and voltages to switch a much higher power circuit for many thousands of cycles. This makes them an excellent choice for controlling electric motors.
Electromechanical relays are switches that transfer signals via the connection of mechanical contacts to open and close the output circuit. These relays are used when a low-power signal is needed in order to control one or more circuits.
Forcibly guided relays are electromechanical switching devices that are designed in such a way that it is not possible for all contacts to be closed at the same time. If a normally open contact fails when trying to open, the associated normally closed contact cannot close when the power supply is switched off.
Monitoring relays are protective control devices that receive input signals, measure them according to a given parameter and output an alarm signal if a threshold is reached. Monitoring relays are more sophisticated than regular relays because they have adjustable operating conditions that can monitor voltage, temperature, current, and other analog signals.
Safety relays are electromechanical switching devices that are designed to implement safety functions and reduce risk. When an error occurs or a detection zone is violated, the safety relay will initiate a safe and reliable response.
Solid state relays are electronic switching devices that switch on and off with a small input voltage to control a larger output voltage or current. Because solid state relays use semiconductors or electronics to transfer signals, there are no moving subcomponents, resulting in faster performance, less noise emitted and a longer lifespan.
Smart relays are small-scale PLCs designed for simple automation tasks where lower I/O points are required. These tasks include: counting, timing, arithmetic functions, storage, etc. A single smart relay can take the place of many control devices by streamlining and combining controls from many pieces of equipment.
Different types of relays, such as electromagnetic relays, solid state relays, and time delay relays, have specialized components or functions for specific applications.
Click here for more about what a relay is and how it works.
Click here for things you must know about relays.
Click here for more about the differences between relays and contactors.
Click here for more about the differences between single-throw and double-throw relays.
Click here for instructions on how to wire a relay.
Click here for more about the differences between electromechanical and solid state relays.
FAQ
What are poles in a relay?
Poles refer to the number of isolated, energizing circuits that can pass through the switch. A single-pole contact (SP) can carry current though one energizing circuit at a time, while a double-pole contact (DP) can simultaneously carry current through two energizing circuits. Three-pole contacts (3P) and four-pole contacts (4P) are also common, but relays with up to 12 poles are possible.
What are throws in a relay?
Throws refer to the number of closed contact positions that are available per pole on a switch. A single-throw contact (ST) controls one contact circuit, while a double-throw contact (DT) controls two. Throws that are normally open (NO) are open by default. This means that until a current passes through the pole (the energizing circuit) the throw (the contact circuit) is not closed and no current is passing through it. When the contact circuit is closed the current passes through the now completed circuit. Throws that are normally closed (NC) are closed by default. This means that a until a current passes through the pole (the energizing circuit) the throw (the contact circuit) is closed and the current is passing through it. When the contact circuit is open the current no longer passes through the incomplete circuit.