EET 110 – Survey of Electronics Chapter 21 – Direct Current & Alternating Current Chapter 22 – Low Voltage Signal Systems

Direct Current Current that flows in only one direction in a circuit. Polarity (+ and – terminals) of the source are fixed.

Alternating Current Direction and amplitude of current changes at regular intervals Polarity of the AC terminals changes – resulting a reversal of current flow

AC Generation A wire is moved in a magnetic field OR a magnetic field is moved near a wire. The mechanical energy (motion) is converted to electrical energy by moving the electrons

Left Hand Rule

AC Generation

Sinusoid Waveforms

Waveform features Period (T) – length of TIME to complete one cycle of waveform Frequency (f) – number of cycles completed per second f = 1/T

Waveform size Measurements include Peak amplitude Peak to Peak amplitude Average value ‘effective’ value Also known as RMS (Root Mean Squared) value

Peak Value

Peak to Peak value

Average/Effective value It is obvious that the average of a sine wave is zero. However, an average voltage is delivered. If we look at ½ wave, we can calculate that A(average) = (2/  )A(peak) Or A(average) =.637 A(peak) Effective is Arms =.707 Ap

Sinusoid by angle measurement

Three-Phase AC Phase the the angular separation or difference between two sinusoids It is possible for three separate ‘phases’ to be delivered, each separated by 120 degrees Wired as either Wye or Delta

DC Generation Since the voltage/current in the wire changes polarity – we have to correct for this to get DC There are two ways to do this Mechanically – slip rings Electronically – Diodes

DC Generation Otherwise, generators vary by How we get the magnetic field Permanent magnet Separate field coils Self excitation Prime Mover What supplies the mechanical motion Water Steam …

Assignment Problems 1 & 2

EET 110 – Survey of Electronics Chapter 22 – Low Voltage Signaling Systems

Examples of LV systems Door Chime Burglar alarm systems Annunciator systems Telephone Circuits Cable pair Switched network Dialing –tone versus pulse

Alarm Systems Sensors Entry open window/door Glass monitor Passive Infra Red Heat Motion Panic Button Floor Switch