In PLC ladder logic for a valve control with start and stop, which approach represents a proper latch/holding circuit?

In PLC ladder logic for a valve control with start and stop, which approach represents a proper latch/holding circuit?

• A. Use a latch that is energized directly by the start pushbutton.
• B. Use a latch/holding contact: start pushbutton in series with a memory bit coil; the coil output latches through a normally open contact of the same memory bit; stop button resets the memory bit.
• C. Use a timer to delay turning on the valve.
• D. Use a separate CPU to manage the latching.

Answer: (B)