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14 Cards in this Set
- Front
- Back
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Poles described the number of... |
Isolated circuits that can pass through a relay at one time |
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Throw is the number of different... |
Closed contact positions per pole |
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Break is the number of... |
Separate contacts used to open or close individually circuits |
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What are the 2 most common failure causes of relays |
Contamination and mechanical wear |
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If dual relays are used in parallel to increase reliability, each relay should be capable of handling... |
The full current of the load |
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Why is it not recommended to parallel two 5A to control a 10 A load? |
They tend to not turn on at the same time. And Both relays should be able to handle the full current incase 1 stops working |
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Why Is it sometimes necessary to derate the continous current of relay contacts when controlling some loads? |
Some have high current/voltage spikes when started/stopped |
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Why should the voltage to energize or trigger a relay be at least 110% of the min rated energize voltage |
Operation of a relay at less then nominal ratings can result in switching failures or increased switching times |
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Why should the voltage drop out or de energize a relay be less then 90% of the max rated coil dropout voltage |
If not derated the voltage may not turn off |
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Relays most commonly fail in the.. |
Stuck open |
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In some applications solid state relays are preferred over electromechanical relays du to.. |
Decreased chatter noise, increased reliability, and more consistent performance with age (depends on environment)
Ssr are more resistant to shock and vibrations, faster response time, and no contact bounce |
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2 types of relays |
Mechanical and solid state |
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Solid state relays dont have actual coils and contacts.. instead they use.. |
Semiconductor switching devices such as transistors, rectifiers. SSR have no moving parts. |
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Types of contamination.. |
Metallic- causes shorted conditions Non metallic- creates an open circuit. |
