Timers Flashcards
What are the three types of timers?
Dashpot
Motor Driven
Solid State
How does the dashpot timer work?
Uses airflow. either a bellow or diaphragm adjusted by a set screw valve
How does a motor driven timer work?
It uses a small synchronous motor controlled by the supply voltage frequency to control a synchronous clock
What kind of contacts does a motor driven timer have?
It has both timing contacts and instantaneous contacts
What does the shaded coil/ ring do?
It keeps contacts closed on all AC coils when the sine wave reaches zero sixty times a second
Uses lenz’s law principle like the shaded pole motor
What does the solid state timer use to control the time rate?
A resistive/ capacitive circuit to control time rate
What is the most accurate timer?
The solid State timer
What are the functions of solid state timers?
On-Delay
Off-Delay
Repeat/recycle
One Shot
Reset
What is the only drawback of the solid state timer?
They do not have instantaneous contacts like the motor driven timer and the Allen Bradley pneumatic timer
What happens when the solid state timer is on Repeat/ Recycle function?
The timing function happens over and over as long as power is applied
Example- Traffic Lights and Flashers
What happens when the solid state timer is on the reset function?
The timing function only happens once and must be de-energized and then re-energized to happen again
What happens when the solid state timer is on the One Shot function?
When power is applied the contacts change state and the timing also begins
What are the two types of solid state connections?
8 pin and 11 pin
What timer is usually one function and has a shorter time delay?
8 pin
What timer usually has multiple functions and a high time delay?
11 pin
What are the methods of stopping motors?
Plug Brake
Friction Brake
AC friction brake
DC motor break
What is a plug brake?
Designed to stop a motor abruptly using counter
What is a friction brake?
it uses brake pads or a friction belt as its stopping force and is controlled by a solenoid. When power is off or lost the motor can not rotate
What is the AC electric break?
Used to control the rate that an a motor can stop.
How does an AC electric break work?
Uses DC injection into the motor starters windings when AC power is removed
This creates a non rotating DC electromagnetic field that cuts into the rotor bars and stops rotation.
What is regenerative?
The Energy is either sent back to the electrical system or a battery bank for recharging
