As shown in figures "A", "B", "C", and "D"...

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Question 1 of 205eccefa5bacbc34ba4d4887b

As shown in figures "A", "B", "C", and "D" of the illustrated PLC controlled heating system, in addition to the clock timer, run and stop contacts all being closed, what other input requirements must be met for the boiler to be firing? See illustration EL-0260.

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🔍 Key Concepts

• PLC ladder logic: how series contacts represent an AND condition and parallel branches represent an OR condition. • Relationship between the space air, tank water, and boiler water sensor contacts in the ladder diagram (Figure C). • How the timing diagram in Figure D shows which contacts are closed when the Boiler output turns ON.

💭 Think About

• Look closely at Figure C: are the three sensor contacts drawn strictly one-after-another in a single line, or are any of them branched in parallel? What does that mean in terms of AND vs OR logic? • Compare the periods when each sensor is marked "Closed" in Figure D to the period when the Boiler output is "On". Which sensors are closed every time the Boiler is on, and which are not always closed? • From that, decide which sensor (if any) is absolutely required to be closed, and whether at least one, two, or all three must be closed together for the boiler to fire.

✅ Before You Answer

• Verify in Figure C whether the sensor contacts are in series or parallel ahead of the clock timer, run, and stop contacts. • Check in Figure D that whenever the Boiler row shows "On", the required sensor rows above also show Closed for the same time interval. • Confirm that your chosen answer exactly matches that logical requirement (for example, "ALL closed" vs "one specific sensor plus either of the others").

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