AC (Alternating current)-An electric current that rises to a maximum in one direction falls back to zero and then rises to a maximum in the opposite direction and then repeats. The electricity in ordinary home or office outlets is AC. Alternating current differs from direct current (DC) in that its direction is reversed 60 times per second (50 times per second in some countries), while DC current flows in one direction only whether pulsed or steady.

Ampere (Amp)-Unit of electrical current

Amp-hour (Ah)-Unit of electrical current

Amplifier- A circuit that increases the voltage, current, or power of a signal.

Analog- Information represented as continuously varying voltage or current rather than in discrete levels as opposed to digital data varying between two discrete levels.

AWG- Abbreviation for "American wire gauge". A gauge that assigns a number value to the diameter of a wire.

Battery- A DC voltage source containing two or more cells that convert chemical energy to electrical energy. The most commonly used battery in the security industry is a Sealed-Lead-Acid back-up or stand-by battery.

Circuit- Interconnection of components to provide an electrical path between two or more components.

Circuit Breaker- A protective device used to open a circuit when current exceeds a maximum value - in effect, a reusable fuse.

Closed Circuit- Circuit having a complete path for current flow.

Contact- Current carrying part of a switch, relay or connector.

Current– Current is the quantity of electrons passing a given point. Current is like the water flowing through a pipe, while voltage is like the water pressure.

Current draw- Amount of current a device needs to operate

Dead Short - Short circuit having zero resistance.

DC (Direct current)- An electric current flowing in one direction only.

Decibel - (dB)a logarithmic representation of gain or loss. Siren volume is rated in dB.

Digital- Relating to devices or circuits that have outputs of only two discrete levels. Examples: 0 or 1, high or low, on or off, true or false etc.

Fuse- A protective device in the current path that melts or breaks when current exceeds a predetermined maximum value.

Ground - An intentional or accidental conducting path between an electrical system or circuit and the earth or some conducting body acting in place of the earth. A ground is often used as the common wiring point or reference in a circuit.

Impedance- (Z) Measured in ohms it is the total opposition to the flow of current offered by a circuit. Impedance consists of the vector sum of resistance and reactance.

Jack- Socket or connector into which a plug may be inserted.

LED- Abbreviation for "light emitting diode."

Linear– The relationship between input and output in which the output varies in direct proportion to the input.

Mhos- Unit of conductivity - the opposite of Ohms.

Mil- One thousandth (0.001) 1 Amp (A) = 1,000 milliamp (mA)

Negative– A terminal that has an excess of electrons.

Normally Closed– A designation, which states that the contacts of a switch or relay are closed or connected when at rest. When activated, the contacts open or separated.

Normally Open– A designation, which states that the contacts of a switch or relay are normally open or not connected. When activated the contacts close or become connected.

Ohm- Unit of resistance symbolized by the Greek capital letter omega (Ù) – the opposite of Mhos.

Parallel– A circuit having two or more paths for current flow, also called shunt.

Polarity- Term used to describe positive and negative charges.

Positive- Polarity of point that attracts electrons as opposed to negative, which supplies electrons.

Power– The work performed by an electrical current, with the unit of power being the watt.

Power Supply- Electrical equipment used to deliver either AC or DC voltage - can be Linear or Switching.

• Linear:A linear regulated supply maintains a constant output voltage by throwing away the difference between input and output voltage times current as heat. Linear power supplies are classified as such because they eliminate excess energy (power) by dissipating heat to the surrounding air. This form of conversion is simple and thus was the first to be used for power supplies. Simplicity also constitutes the major advantage of linear power supplies. The major disadvantage to them is their lack of efficiency, usually only 30-50%.

• Switching:A switching power supply, or switcher, maintains a constant output voltage by storing the difference between input and output voltage times current in a magnetic field, then periodically drawing out this stored energy. The latter device is much more efficient. There are both advantages and disadvantages of a switching mode power supply versus a linear supply. The major advantage is the increased efficiency, upwards of 80% in some cases as well as minimized space. However in order to achieve this efficiency, increased complexity and RF interference are introduced.

• The difference between linear and switching mode power supplies is the regulators. The switching mode regulator converts the DC input to an AC output through the use of a switch. This AC waveform can then be filtered back to a DC value. Instead of dissipating the proper amount of heat as in a linear regulator, the output of a switching mode regulator is controlled by the duty cycle of the switch, i.e. the percentage of time the switch is on.

PTC– Positive thermal coefficient circuit breaker.

Relay– An electromechanical device that opens or closes contacts when a current is passed through a coil.

Self contained Siren– A speaker complete with an electronic siren driver circuit board.

Siren driver– An electronic circuit board that generates sounds to be played through a speaker.

Structured Wiring– A planned wiring method by which all services (phone, data, television, music, and security) originate from a central location or hub.

Volt- Unit of potential difference or electromotive force. One volt is the potential difference needed to produce one ampere of current through a resistance of one ohm.

Wire– Single, solid, or stranded group of conductors having a low resistance to current flow. Used to make connections between circuits or points in a circuit.

Wire Gauge- American wire gauge (AWG) is a system of numerical designations of wire diameters.

Wireless- Term describing radio communication that requires no wire between two communicating points.

Yelp (Siren Sound)- Yelp is a common term in the security industry used to describe a specific type of noise generated by a siren driver or a control panel. The sound could be described as a fast woo-woo sound.