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Definition
| Part inside a switch that completes the flow path for current. Used in all types of switches and relays, including limit switches, pushbutton switches, and reed switches. |
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Term
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Definition
| A switch that physically senses when something is in a specific position, and then either opens or closes the contacts. Common application is valve position indication |
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Definition
| Contacts in a casing that either open or close when a magnet is passed nearby. |
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Term
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Definition
| Manual switch, spring return, either NORMALLY OPEN or NORMALLY CLOSED. |
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Term
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Definition
| Used to select from 3 or more connections |
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Definition
| Used to limit the current flowing through a circuit |
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Definition
| Switching device, which often uses a coil and linkage to operate contacts. |
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Term
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Definition
| Composed of wire wrapped around an air core. When current is passed through the coil, it creates a magnetic field inside the core and draws a magnetic slug into it. This slug is then connected to a mechanical device, through linkages, which operate contacts. |
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Term
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Definition
Used for valve position indication and pump/motor status.
Valves: Green – CLOSED, Red – OPEN, Both – INTERMEDIATE
Pumps/Motors: Green – OFF, Red – ENERGIZED |
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Term
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Definition
| Used to convert small electrical signal into a larger signal to be used for control circuitry. |
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Term
Discuss failure modes of a Typical Automatic Valve Control Circuit |
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Definition
If, while the valve is open, a loss of 125 VDC occurs, the K3 relay will de-energize, which will release the open signal, and the valve will close. |
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Term
| Discuss failure modes of a typical Valve Control Circuit |
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Definition
If LS-2 or LS-3 fails open or closed, that will affect only the position indicating lamps and will not affect valve operations. However, these lamps must be functional for safe and proper plant operations.
If LS-1 fails open, the K2 relay will not become energized, which will prevent the alarm from being energized in the event that the valve does not come off its closed seat after 10 seconds of trying to open it. |
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Term
| Discuss failure modes of a typical Valve Motor Control Circuit |
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Definition
If LS-3, 4, or 5 fail in either position, actual valve operations will still be possible, however, the valve position indications and alarm will not function.
If LS-1 fails open, the valve will not be able to be opened.
If LS-2 fails open, the valve will not be able to be closed. |
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