alarm circuits

What is a micro switch?

A small, sensitive switch commonly used onboard ships, activated by very little physical force, typically used for position sensing.

What are the criteria for selecting a limit switch?

• Contact rating (AC or DC)

• Current life expectancy of contacts

• Contact bounce impact on control circuits

• Physical size of switch

• Required movement to operate

• Effect of over-run

• Environmental impact

• Protection needed (e.g. waterproofing)

What does "contact bounce" mean in a limit switch?

It refers to the rapid, unintended on/off switching as contacts settle, which may disrupt control circuits.

What is an electrical relay?

A device that uses a small electrical input to control a larger output load by activating an internal electromagnet to open/close contacts.

Describe the basic components of a relay.

• Electromagnet coil

• Pivoted armature

• Spring (returns armature when de-energized)

• Output contacts: COM (Common), NO (Normally Open), NC (Normally Closed)

How does a relay work?

• When coil is energized by a small input (e.g., 20 mA), it pulls the armature.

• This action switches the output contacts to control a larger current load.

• When coil is de-energized, the spring pulls armature back.

What types of coils are used in relays?

AC or DC coils, with operating voltages up to ~240V DC or 440V AC.

Does the coil voltage affect the output circuit voltage in a relay?

No. The coil voltage (e.g. 12V DC) is independent of the output switch voltage (e.g. 120V AC).

What are two key advantages of using electrical relays in circuits?
A:

1. Small input current can control larger output loads.

2. Output circuit is electrically isolated from input, reducing shock or short circuit risk.