The relay is an electro-mechanical switch, consisting of a coil, an armature, and contacts.
A current passes through the coil creating a magnetic field that attracts the armature, causing the contacts to move, either making or breaking a connection. The following contacts are known by how they can be thrown:
Ship Normally open contacts (NO)
When the relay is activated, NO contacts connect the circuit and will disconnect the circuit when it is inactive.
Ship Normally closed contacts (NC)
NC contacts disconnect the circuit when the relay is activated and connect when inactive.
Ship Changeover contacts (CO)
The contacts have a common terminal and control two circuits. One is a NO contact and the other is an NC contact. It is also known as a ‘double throw'(DT),
Single Pole Single-Throw contacts on ship (SPST)
These have two terminals that can be connected or disconnected (11-12 or 13-14) and two terminals for the coil. The terminology ‘SPNO’ and ‘SPNC’is sometimes used to indicate the contacts’ de-energized state (Figure b).
Double Pole Single-Throw contacts on ship (DPST)
The relay has four terminals that can be connected or disconnected. This is equivalent to two SPST switches actuated by a single coil and has two terminals for the coil (Figure c).
Single Pole Double-Throw contacts on ship (SPDT)
With a total of five terminals, two for the coll, a further terminal connects to two others as a CO contact (Figure d).
Double Pole Double-Throw
Single Pole Single-Throw contacts on ship (SPST)
These have two terminals that can be connected or disconnected (11-12 or 13-14) and two terminals for the coil. The terminology ‘SPNO’ and ‘SPNC’is sometimes used to indicate the contacts’ de-energized state (Figure b).
Double Pole Single-Throw contacts on ship (DPST)
The relay has four terminals that can be connected or disconnected. This is equivalent to two SPST switches actuated by a single coil and has two terminals for the coil (Figure c).
Single Pole Double-Throw contacts on ship (SPDT)
With a total of five terminals, two for the coll, a further terminal connects to two others as a CO contact (Figure d).
Double Pole Double-Throw contacts on ship (DPDT)
This has eight terminals with two rows of CO contacts. It is equivalent to two SPDT relays actuated by a single coil (Figure e).
Ship miniature relays are also subdivided by their operation:
Non-Latching (stable type)
A relay that is activated when the coil Is energized and turns off when de-energized. Non-latching relays are used In control applications when the switch must return to a neutral state if power is lost.
Latching type relays on ship system
Latching relays are used when power consumption and dissipation are limited. For example, after the Initial actuation of the relay no further power is needed to maintain the state.
1 One Coil Latching Type
This relay uses a pulse input to a single coil and a latching mechanism to maintain the contact as either on or off. By applying signals of opposite polarities the relay is set and reset.
2 Two Coil Latching Type
This relay uses a latching construction and two coils, one to set and another to reset. Setting and resetting is achieved by applying pulse signals of the same polarity.
Miniature relays are designed so that the casing does not become detached under normal use, as performance could be reduced. Consequently, the DIN rail mounting system allows simple replacement of malfunctioned relays. A PCB (Printed Circuit Board) miniature relay, socket-mounted ‘ice cube miniature relays and their terminal designation.
Miniature relays are assembled into control cabinets with their sockets, which can in general be subdivided into two basic types:
- Screw terminals sockets miniature relays
- Screwless terminals sockets (for fast wiring).
All sockets are either panel- or 35 mm rail-mounted (EN 60715). Socket’s terminals as well as relays’ contacts pins are assigned with reference numbers, which should be used when troubleshooting to verify the condition of the contact in an energized and de-energized state.
