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Time-Delay Electromechanical Relays
19 questions By Tony R. Kuphaldt
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Question 16 of 19
A simple time-delay relay may be constructed by connecting a large capacitor in parallel with the relay coil, like this:
Explain how this circuit works, and also determine what type of time-delay relay function is provided by it (NOTO, NOTC, NCTO, or NCTC).
Reveal answerNormally-closed, timed-closed (NCTC).
Follow-up question: what purpose does the diode serve in this circuit?
Notes:For substantial time delays (many seconds) on large relays (high-current coils), the capacitor must be huge, making this a somewhat impractical circuit for all but miniature relays.
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Question 17 of 19
Suppose you needed to build a circuit that pulsed a lamp on and off (once) when a pushbutton is released. In other words, you wanted the lamp to do this:
Draw a ladder logic diagram for a circuit that would fulfill this function, using at least one time-delay relay.
Reveal answer
Notes:This is a good problem-solving exercise, figuring out how to creatively combine time-delay relays to perform a specific function.
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Question 18 of 19
Suppose you needed to build a circuit that delayed the energization of a lamp when the button was pushed, and also delayed its turning off when the button was released. In other words, you wanted the lamp to do this:
Draw a ladder logic diagram for a circuit that would fulfill this function, using at least one time-delay relay.
Reveal answer
Follow-up question: which relay controls the on-delay time, and which relay controls the off-delay time?
Notes:This is a good problem-solving exercise, figuring out how to creatively combine time-delay relays to perform a specific function.
