Overview Of Control (Ice Cube) Relays
https://engrtechnologies.blogspot.com/2014/02/overview-of-control-ice-cube-relays.html
Overview Of Control (Ice Cube) Relays
Introduction
An electromechanical relay
is an electrical switch actuated by an electromagnet
coil. As switching devices, they exhibit simple “on” and “off” behavior with no
intermediate states.
The electronic schematic symbol for
a simple single-pole, single-throw (SPST) relay is shown here:
SPST relay (NO contact)
A coil of wire wrapped around a laminated
iron core provides the magnetic field necessary to actuate the switch
mechanism. This particular relay is equipped with normally open (NO) switch contacts, which means the switch will be in the open (off) state
when the relay coil is de-energized.
A single-pole, single-throw relay
with a normally-closed (NC) switch contact would be represented
in an electronic schematic like this:
In the electrical control world, the
labels “Form-A” and “Form-B” are synonymous with “normally
open” and “normally closed” contact status. Thus, we
could have labeled the SPST relay contacts as “Form-A” and “Form-B,” respectively:
A further extension on this theme is
the double-pole, double-throw (DPDT) relay contact. This design
of switch provides two sets of Form-C contacts in one unit, simultaneously
actuated by the electromagnet coil:
DPDT relays are some of the most
common found in industry, due to their versatility. Each Form-C contact set offers a choice of either
normally-open or normally-closed contacts, and the two sets (two
“poles”) are electrically isolated from each other so they may be used in
different circuits.
A DPDT “ice cube”
relay is shown in the following photographs, ready to be plugged into its base
(left) and with the plastic cover removed to expose both sets of Form-C
contacts (right):
These relays connect to the socket
with eight pins: three for each of the two Form-C contact set, plus two more
pins for the coil connections. Due to the pin count (8), this style of relay
base is often referred to as an octal base.
A closer view of one Form-C contact
shows how the moving metal “leaf ” contacts one of two stationary
points, the actual point of contact being made by a silver-coated “button” at
the end of the leaf. The following photographs show one Form-C contact
in both positions:
Industrial control relays usually
have connection diagrams drawn somewhere on the outer shell to indicate which
pins connect to which elements inside the relay.
The style of these diagrams may vary
somewhat, even between relays of identical function. Take for instance the
diagrams shown here, photographed on three different brands of DPDT relay:
Bear in mind that these three relays
are identical in their essential function (DPDT switching), despite differences
in physical size and contact ratings (voltage and current capacities). Only two
of the three diagrams shown use the same symbols to represent contacts, and all
three use unique symbols to represent the coil.