Water Billing System

Topics: Relay, Alternating current, Voltage Pages: 77 (19504 words) Published: September 7, 2011
Relay Technical Information

Definition of Relay Terminology
(also referred to as primary or input) • Nominal Coil Voltage (Rated Coil Voltage) A single value (or narrow range) of source voltage intended by design to be applied to the coil or input. • Pick-Up Voltage (Pull-In Voltage or Must Operate Voltage) As the voltage on an unoperated relay is increased, the value at or below which all contacts must function (transfer). • Drop-Out Voltage (Release or Must Release Voltage) As the voltage on an operated relay is decreased, the value at or above which all contacts must revert to their unoperated position. • Maximum Continuous Voltage The maximum voltage that can be applied continuously to the coil without causing damage. Short duration spikes • Coil Designation Single side stable type Non-polarized Polarized 1 coil latching type —

of a higher voltage may be tolerable, but this should not be assumed without first checking with the manufacturer. • Nominal Operating Current The value of current flow in the coil when nominal voltage is impressed on the coil • Nominal Operating Power The value of power used by the coil at nominal voltage. For DC coils expressed in watts; AC expressed as volt amperes. Nominal Power (W or VA) = Nominal Voltage × Nominal Current. • Coil Resistance This is the DC resistance of the coil in DC type relays for the temperature conditions listed in the catalog. (Note that for certain types of relays, the DC resistance may be for temperatures other than the standard 20°C 68°F.)

2 coil latching type 4-terminal 3-terminal




or —




A black coil represents the energized state. For latching relays, schematic diagrams generally show the coil in its reset state. Therefore, the coil symbol is also shown for the reset coil in its reset state.

CONTACTS (secondary or output)
• Contact Forms Denotes the contact mechanism and number of contacts in the contact circuit. • Contact Symbols Form A contacts (normally open contacts)

Form A contacts are also called N.O. contacts or make contacts. Form B contacts are also called N.C. contacts or break contacts. Form C contacts are also called changeover contacts or transfer contacts. • MBB Contacts Abbreviation for make-before-break contacts. Contact mechanism where Form A contacts (normally open contacts) close before Form B contacts open (normally closed contacts). • Rated Switching Power The design value in watts (DC) or volt amperes (AC) which can safely be switched by the contacts. This value is the product of switching voltage × switching current, and will be lower than the maximum voltage and maximum current product.

• Maximum Switching Voltage The maximum open circuit voltage which can safely be switched by the contacts. AC and DC voltage maximums will differ in most cases. • Maximum Switching Current The maximum current which can safely be switched by the contacts. AC and DC current maximums may differ. • Maximum Switching Power The upper limit of power which can be switched by the contacts. Care should be taken not to exceed this value. • Maximum Carrying Current The maximum current which after closing or prior to opening, the contacts can safely pass without being subject to temperature rise in excess of their design limit, or the design limit of other temperature sensitive components in the relay (coil, springs, insulation, etc.). This value is usually in excess of the maximum switching current. • Maximum Switching Capability The minimum value of voltage and current which can be reliably switched by the contacts. These numbers will vary from device type to device type. Factors affecting minimums include contact material, contact pressure, wipe, ambient conditions and type of relay enclosure (sealed vs. non-sealed). • Maximum Switching Capacity This is listed in the data column for each type of relay as the maximum value of the contact capacity and is an interrelationship of the...
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