Relays Flashcards
What do relays do?
Relays are electrically operated switches that control high-power circuits using low-power signals.
How do relays work?
When a current flows through the coil, it creates a magnetic field that pulls a movable contact to open or close the circuit.
What are the main types of relays?
Electromechanical relays (EMRs) and solid-state relays (SSRs).
What is an electromechanical relay (EMR)?
A relay that uses a physical coil and moving contacts to switch a circuit.
What is a solid-state relay (SSR)?
A relay that uses semiconductor components like thyristors or transistors to switch circuits without moving parts.
What is a single-pole single-throw (SPST) relay?
A relay with one input and one output, functioning as a simple on/off switch.
What is single-pole double-throw (SPDT) relay?
A relay with one input and two outputs, allowing the circuit to toggle between two paths.
What is a double-pole double-throw (DPDT) relay?
A relay that can control two independent circuits and toggle between two paths for each.
What is a latching relay?
A relay that maintains its state (on or off) even after the actuating current is removed.
What is a reed relay?
A relay with contacts sealed in a glass tube, operated by a magnetic field.
What is the coil voltage rating of a relay?
The voltage required to activate the relay’s coil, such as 5V, 12V, or 24V.
What is the contact rating of a relay?
The maximum voltage and current the relay contacts can handle, e.g., 250V AC, 10A.
What is the switching speed of a relay?
The time it takes for the relay to switch states, typically measured in milliseconds.
What is the difference between normally open (NO) and normally closed (NC) contacts?
NO contacts remain open until relay is activated; NC contacts remain closed until activated.
How do you use a relay in a circuit?
Connect the control signal to the coil terminals and the load circuit to the contact terminals.
What is a flyback diode in a relay circuit?
A diode placed across the relay coil to prevent voltage spikes when the coil is de-energised.
What is a relay’s life expectancy?
The number of switching cycles it can perform before failure, typically 10,000 to 1,000,000 cycles.
What is a thermal relay?
A relay that operates based on temperature changes, often used for motor protection.
What is a thermal relay?
A relay that operates based on temperature changes, often used for motor protection.
What is a relay module?
A pre-assembled circuit containing a relay and additional components for easy integration with microcontrollers.
What is the purpose of an auxiliary relay?
To provide additional contacts or functionality to the primary relay in complex systems.
What is a common issue with electromechanical relay?
Contact wear or pitting due to arcing during switches.
What are the advantages of solid-state relays over electromechanical relays?
Faster switching, no moving parts, longer lifespan, and silent operation.
What are the disadvantages of solid-state relays?
Higher cost, potential heat generation, and susceptibility to voltage spikes.
How do you test a relay?
Use a multimeter to check the coil resistance and verify continuity between the contacts when the relay is activated.
What is a relay’s pickup voltage?
The minimum voltage required to activate the relay’s coil.
What is a relay’s dropout voltage?
The voltage at which the relay deactivates and returns to its default state.
How do you prevent relay chattering?
Use a properly rated power supply and avoid fluctuating control signals.
What is a zero-crossing relay?
A solid-state relay that switches at the zero-crossing point of the AC waveform to reduce electrical noise.
What are typical applications of relays?
Motor control, lighting systems, home automation, and industrial machinery.
