ELECTRICAL LOGIC CONTROL COMPONENTS
6.1 Relays
Relay is an electrically operated switch. It consists of a coil with an iron core and one or more movable contacts, switched by the magnetic field of the coil assembly
General purpose relays specially designed for users demanding small size sturdy construction and high electrical capacity. Mechanisms are furnished in polycarbonate dust proof enclosure and are recommended for a multitude of electrical control applications for their reliability and compact size.
When the voltage is applied to the coil an electric current flows through the coil, a magnetic field builds up and causes the armature to be pulled into the core of the winding. The switching position is maintained as long as the voltage is applied. When the voltage is removed the armature is restored to its original position by return spring
Contacts: Contacts are most important parts of relay. Their operation and characteristics are influenced by various factors such as contact materials, applied voltage and current, load type, switching frequency.
Relay functions
- Changing from a NC to NO contact (Inversion)
- Multiplying contacts from one to any reasonable number of contacts
- Power amplification
- Voltage change
- Memory function
Types
Plug in relay
Features
- These are used in low level circuits
- Dust free tight case
- Terminals arrangement facilitates attachment to standard relay socket
Printed Circuit Board relay
Features
- Specially designed for users demanding small size ,sturdy construction and high electrical capacity
- Mechanisms are furnished in polycarbonate dust proof enclosures
- AC or DC actuation with voltages up to 240 V AC or 120 V DC
Solid state relay
Features
- Un limited life time:Un like electromechanical relays and contactors, solid state relays have no moving parts and their life is virtually unlimited
Latching relay:
Features
- Low power consumption due to mechanical latch for economic operation
- Relays with mixed coil specification can be produced
6.2 Timing relays
The function of this type of relay is to close or open the contacts whether normally open or normally closed contacts, in a circuit after a particular time delay which is adjustable.
Types
ON delay
Here when the relay is energized the preset time starts to elapse. Once the preset time is reached the switching position is changed. The position of contacts is maintained as long as voltage is applied.
TIMER
In OFF – Delay
In this timer as soon as the timer is energized, the contacts change its position. The time elapse will start only when the timer is triggered OFF.
6.3 COUNTERS
Counters are devices which count the change of electrical signal state at the counter input. The counters are settable so that if the count exceeds the set value, the switching position of the output contact is changed. In Pneumatics, Counters are used for counting the number of parts processed, or the number of cycles. The Counters shall be of Electromagnetic type or Solid state.
The following types of counters are used
Preset Counter - here the contacts actuate and deliver a switching signal when the preset time is over.
UP- Counters - here the counter counts in ascending order
DOWN Counter – here the counter counts in descending order.
Reversible counters – here the counter shall be programmed for either UP or DOWN
COMMENTS