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.
What is a relay? A relay is an electrically operated switch. Most relays use an electromagnetic to operate the switch. An electromagnet is a device that creates a magnetic field by passing an electrical current through a coil of wire. The magnetic field is then turned off when the current is removed.
Why use relays? Relays are commonly used when there is a need to control a switch with high voltage or circuits with large amounts of current passing through them. Operating these types of switches manually can be dangerous, inefficient and impractical. By using relays, operational safety is increased while also providing the ability to use smaller, safer and less expensive electrical equipment to control devices. Using relays allow for control of several devices on a single switch, as opposed to using several switches for each device. Relays can be combined with timers and logic circuits to assist in electrical automation.
How do relays work? A relay consists of two separate circuits that work together to open or close a switch (or contacts). The first circuit drives the coil (or electromagnet). The electricity passes through the coil, creating a magnetic field. The second circuit contains a set contacts and a separate power source. This circuit is what provides power to the electrical load.
When electricity passes through the coil, it creates a magnetic field. This magnetic field pulls the contact from the other circuit closed (or against the stationary contact) which will allow current to pass through the contacts, therefore allowing the load to become energized. When the coil is de-energized, the magnetic field is gone which allows the contact to be pushed back into its original state, de-energizing the load side of the circuit.
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.