Transcription of UNIT I - INTRODUCTION OF RELAYS
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UNIT I - INTRODUCTION OF RELAYS
UNIT I - INTRODUCTION OF RELAYS A rela y comprises of a n electroma gnet a nd a contact unit. The definition is: Activating the contact unit using electr oma gnetic attraction, which is produced when electr ic curr ent exceeding the specified va lue flows to the electroma gnet; the volta ge a nd current (input signa l) applied to the coil opens or shuts the contact. Rela ys used for i. as inter faces between contr ol circuits and loa d circuits, ii. for signa l multiplication, iii. for separation of dir ect curr ent and alter nating curr ent circuits, infor mation. Functions Number of pins Description 1 2 Normally closed contact 3 4 Normally open contact 5 6 Normally closed contact, time delay 7 8 Normally open contact, time delay 1 2 4 Changeover contact 5 6 8 Changeover contact, time delay A1 A2 The coil terminals (common) relay contacts are either normally open (NO) or normally closed (NC), The term normally refers to the state in which the coil is not energized.
θ is the angle by which S 2 lands S 1.If β 1 = β 2 =90 o, the comparator is called cosine comparator and if β 1 =0 and β 2 =180 o, it is a sine comparator. In short, a phase comparator compares two input quantities in phase angle (vertically) irrespective of the magnitude and operates if the phase angle between them is < 90o. There are two types of phase comparators:
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