Study the ladder logic program in Figure 6-69, and answer the questions that fol
ID: 2072924 • Letter: S
Question
Study the ladder logic program in Figure 6-69, and answer the questions that follow: Under what condition will the latch rung 1 be true? Under what conditions will the unlatch rung 2 be true? Under what condition will rung 3 be true? When PL1 is on. the relay is in what state (latched or unlatched)? When PL2 is on, the relay is in what state (latched or unlatched)? If AC power is removed and then restored to the circuit, what pilot light will automatically come on when the power is restored? Assume the relay is in its latched state and all three inputs are false. What input change(s) must occur for the relay to switch into its unlatched state ? If the examine if closed instructions at addresses I/I, I/2, and I/3 are all true, what state will the relay remain in (latched or unlatched)?Explanation / Answer
a)
Rung 1 is true when push button and pressure switch are closed.I/1 and I/2 are closed
b)
Rung 2 will be true when limit is closed. I/3 is closed.
c)
Rung 3 will be true only when output 0/9 is false i.e de-energized.
d)
When PL1 is on the relay is latched.
e)
When PL2 is on the relay is Unlatched.
f)
PL1 will be on if before power PL1 is in on state.
PL2 will be on if before power cut PL1 is off.
We know once PL1 is on, it will off only by making unlatch zero.
g)
For the relay to be unlatched Rung 2 should be true. i.e limit switch should be closed
h)
If I/1 , I/2 , I/3 are all true the relay will be in unlatched state.
Unlatch condition is used to make output off. It is retentive i.e even if power is gone the output will be on if it on before until unlatch is 1.