Residential Security, Access Control, and Surveillance Copyright © 2005 Heathkit Company, Inc. All Rights Reserved Presentation 1 – Magnetism and Work

2 Objectives At the end of this presentation, you will be able to:

3 Describe how a magnetic field forms around a permanent magnet. Describe the effect of a magnetic field on a reed switch. Explain why it doesn’t take the same amount of magnetic force to hold a reed switch closed as it does to close the switch. Describe how a relay works. Describe how a solenoid works.

4 Magnetic Fields All atoms are surrounded by lines of force called electrical fields. In a similar manner, all magnets are surrounded by a magnetic field. The Magnetic Field which surrounds a magnet is made up of magnetic lines of force.

5 Magnets have a North and South pole. Magnetic Lines of Force surround the entire magnet and are called Flux lines.

6 There are a number of basic rules and characteristics that govern flux lines: Flux lines have direction (polarity). Flux lines always form a complete loop. Flux lines cannot cross one another. Flux lines tend to form the smallest possible loops.

7 Like poles repel because the flux lines repel. Unlike poles attract because the flux lines link and shorten.

8 There are several characteristics that apply to magnets: Flux refers to the complete magnetic field that surrounds the magnet. Flux density refers to the number of flux lines per a unit of area. Induction is the creation of a magnetic field in other materials by passing them through a magnetic flux. Permeability refers to the way a material accepts magnetic flux. Reluctance is an opposition to flux within a material.

9 Magnetic Induction occurs when a magnet causes a magnetic field to form in another object, like this piece of iron. This can also occur if an object with a high permeability remains in close proximity to the magnet.

10 A reed switch is a good example of a mechanism that uses magnetic induction to perform a task. Reed Switch

11

12 Electricity and Magnetism You don’t need a magnet to have a magnetic field. Electrical current can create a magnetic field. Motion is the link between electricity and magnetism. Moving charged particles create a magnetic field. A large number of moving particles creates a larger field. Current flow is the movement of negatively charged electrons. Increasing current flow increases the magnetic field. Single-conductor magnetic field has no practical value.

13 Coiling a conductor improves the magnetic characteristics because this: Brings the flux lines into closer proximity Concentrates the flux lines into the center of the coil Creates a North and South pole. Therefore, a coiled conductor exhibits the properties of a magnet.

14 (Current)

15 Relay

16 Relay Uses Relays allow you to control an electrical circuit from a distance. Relays allow you to control a circuit carrying a large current with a small current. Relays allow you to control one power source with a second power source that is completely isolated from the first power source. Relays with multiple contacts allow you to control several different current paths with a single current.

17 Solenoid

18 Solenoid Construction

19 Solenoid Magnetic Fields Weak Field Strong Field

20 Creating a Third Field

21 Fully Active Solenoid

22 Solenoid Uses Solenoids allow you to control mechanical devices. Open and close valves to regulate fluid control in a mixing process. Latch and unlatch a door locking mechanism. Automate device selection in a storage system. Open and close high-current contacts such as those used to run an automobile starter motor, while at the same time, engaging the starter drive gear with the flywheel ring gear.

Residential Security, Access Control, and Surveillance Copyright © 2005 Heathkit Company, Inc. All Rights Reserved End