Timers and Smart Relays 030204b Flashcards
What are three basic types of timing devices?
Spring-wound interval timers
Mechanical and electronic time switches
Timing relays
What are spring-wound interval timers commonly used for?
Designed to be used as wall switches for lights, fans, bathtub spa motors and sauna heaters.
What are mechanical and electronic time switches commonly used for?
Found in systems that control security lighting, landscape irrigation, and parking receptacle circuits.
What type of timer use a small electrically driven clock motors that control adjustable trip mechanisms or cams to change the state of the contacts?
Mechanical Time switches.
What are three methods of controlling the timing of a timing relay?
Pneumatically (by air)
Fluid-filled dashpot
Electronically.
What are the five basic timing functions provided by timing relays?
TDOE (Time Delay on Energization) also known as on-delay or delay-on-operation.
TDOD (Time Delay on De-energization) also known as off-delay.
Interval timing
One-shot timing
Repeat cycle timing.
How does time delay on energization contacts work?
Once a coil is energized, the contacts will remain in their normal state for a specified amount of time before changing states. Once the coil is de-energized the contacts will revert back to their normal state immediately.
How does time delay on de-energization contacts work?
The coil is energized and the contacts will change state immediately. Once the coil is de-energized the contacts will not revert back to their normal state until after a specified amount of time has passed.
How does interval timing contacts work?
Contacts will change state immediately once a coil is energized and will revert back to their normal state after a specified amount of time even if the coil remains energized.
How does one-shot timing contacts work?
Requires an extra set of terminals to receive a start signal. The relay coil is continuously energized but contacts do not change state until the start signal is received. After the time has passed the contacts revert back to normal state until they receive the start signal again.
How does repeat cycle timing contacts work?
Provides a regular on-and-off cycle for timed contacts. Can be started by the energization of the coil or by a start signal. Typical operation is the contacts will continue to cycle states until the coil is de-energized.
When are smart relays commonly used?
Used in situations where full-scale PLCs (Programmable Logic Controller) are overkill in terms of complexity and cost.
What is a smart relay?
Simple relays and/or timers that are programmable.
What are some deciding factors when choosing a smart relay?
Number of inputs and outputs needed
Required current and voltage ratings
Whether a keypad or digital display is needed
Wireless communication functionality.
How can smart relays be programmed?
Through the relay’s keypad or a computer.
