Star-delta starter using timers in PLC Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start the star contactor using a timer.

PLC Programming

TON TimerStar(IN:=StartButton, PT:=T#[1]s, Q=>StarContactor);

Drag options to blanks, or click blank then click option'

A15

B5

C10

D20

Attempts:

3 left

💡 Hint

Common Mistakes

Using too short or too long timer values that can cause motor damage.

Confusing the timer preset time unit.

The star contactor timer is set to 10 seconds to allow the motor to start in star configuration before switching to delta.

2fill in blank

medium

Complete the code to energize the delta contactor after the star timer is done.

PLC Programming

IF TimerStar.Q THEN DeltaContactor := [1]; END_IF;

Drag options to blanks, or click blank then click option'

AFALSE

BTRUE

CTimerStar.IN

DStartButton

Attempts:

3 left

💡 Hint

Common Mistakes

Setting DeltaContactor to FALSE instead of TRUE.

Using the timer input or start button instead of the timer output.

The delta contactor should be energized (TRUE) when the star timer finishes (Q is TRUE).

3fill in blank

hard

Fix the error in the timer reset logic to stop the star timer when the delta contactor is energized.

PLC Programming

TimerStar.IN := StartButton AND NOT [1];

Drag options to blanks, or click blank then click option'

AStarContactor

BTimerStar.Q

CStopButton

DDeltaContactor

Attempts:

3 left

💡 Hint

Common Mistakes

Using the star contactor or stop button instead of delta contactor.

Not negating the condition to reset the timer.

The star timer input should be reset (set to FALSE) when the delta contactor is energized to prevent overlap.

4fill in blank

hard

Fill both blanks to complete the logic that ensures the star contactor turns off when the delta contactor turns on.

PLC Programming

StarContactor := StartButton AND [1];
DeltaContactor := TimerStar.Q AND [2];

Drag options to blanks, or click blank then click option'

ANOT TimerStar.Q

BNOT StarContactor

CStartButton

DTimerStar.IN

Attempts:

3 left

💡 Hint

Common Mistakes

Not negating the timer output or star contactor in the conditions.

Using the start button incorrectly in delta contactor logic.

The star contactor is ON only when the timer is not done (NOT TimerStar.Q). The delta contactor is ON only when the timer is done and the star contactor is OFF (NOT StarContactor).

5fill in blank

hard

Fill all three blanks to create a dictionary that maps each contactor to its timer status and control signal.

PLC Programming

contactor_status = {
  '[1]': TimerStar.Q,
  '[2]': StartButton,
  '[3]': DeltaContactor
}

Drag options to blanks, or click blank then click option'

AStarContactor

BTimerStar

CDeltaContactor

DStartButton

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up keys and values in the dictionary.

Using variable names instead of string keys.

The dictionary keys are the contactor names: StarContactor, StartButton, and DeltaContactor. Their values are the timer output, start button signal, and delta contactor status respectively.

Practice

1. What is the main purpose of using timers in a star-delta starter circuit?

easy

A. To control the time the motor stays connected in star and delta modes

B. To increase the motor speed instantly

C. To change the motor direction automatically

D. To measure the motor temperature

Solution

1. Step 1: Understand star-delta starter function

   The star-delta starter reduces starting current by initially connecting the motor in star mode, then switching to delta mode.

2. Step 2: Role of timers in this process

   Timers control how long the motor stays in star mode before switching to delta mode to ensure smooth transition and reduce electrical stress.

3. Final Answer:

   To control the time the motor stays connected in star and delta modes -> Option A

4. Quick Check:

   Timers control connection time = A [OK]

Hint: Timers manage star and delta connection duration [OK]

Common Mistakes:

• Thinking timers increase motor speed
• Confusing timers with direction control
• Assuming timers measure temperature

2. Which of the following is the correct way to declare a timer in a PLC program for star-delta starting?

easy

A. TIMER Timer1 (START=Start, TIME=5s, DONE=Done)

B. TON Timer1 (IN:=Start, PT:=T#5s, Q=>Done)

C. TON Timer1(IN:=Start, PT:=T#5s, Q=>Done);

D. Timer1 = TON(Start, 5)

Solution

1. Step 1: Identify correct timer syntax in PLC

   In IEC 61131-3 standard, TON timers are declared with input IN, preset time PT, and output Q using := and => operators.

2. Step 2: Compare options

   TON Timer1 (IN:=Start, PT:=T#5s, Q=>Done) uses correct syntax: TON Timer1 (IN:=Start, PT:=T#5s, Q=>Done). Others have syntax errors or incorrect format.

3. Final Answer:

   TON Timer1 (IN:=Start, PT:=T#5s, Q=>Done) -> Option B

4. Quick Check:

   Correct IEC timer syntax = B [OK]

Hint: Use TON with IN:=, PT:=, Q=> for timers [OK]

Common Mistakes:

• Using incorrect assignment operators
• Missing time format T#5s
• Adding semicolons inside declarations

3. Given the following PLC code snippet for a star-delta starter:

IF Start THEN
  TimerStar(IN:=TRUE, PT:=T#10s);
  IF TimerStar.Q THEN
    TimerDelta(IN:=TRUE, PT:=T#5s);
  END_IF
END_IF

What is the output state of TimerDelta.Q after 12 seconds of Start being TRUE?

medium

A. TRUE

B. TimerDelta.Q resets to FALSE

C. Undefined

D. FALSE

Solution

1. Step 1: Analyze TimerStar behavior

   TimerStar starts when Start is TRUE and runs for 10 seconds. After 10 seconds, TimerStar.Q becomes TRUE.

2. Step 2: Analyze TimerDelta behavior after TimerStar.Q

   Once TimerStar.Q is TRUE (after 10s), TimerDelta starts and runs for 5 seconds. At 12 seconds, TimerDelta has been running for 2 seconds, so TimerDelta.Q is still FALSE. But the code only sets TimerDelta.IN to TRUE when TimerStar.Q is TRUE, so TimerDelta is active.

3. Step 3: Re-examine timing

   At 12 seconds, TimerDelta has been running for 2 seconds (less than 5s), so TimerDelta.Q is FALSE.

4. Final Answer:

   FALSE -> Option D

5. Quick Check:

   TimerDelta.Q after 2s < 5s = FALSE [OK]

Hint: Timer output Q is TRUE only after preset time PT [OK]

Common Mistakes:

• Assuming TimerDelta.Q is TRUE immediately
• Ignoring timer preset times
• Confusing timer input IN with output Q

4. Identify the error in this star-delta timer PLC code snippet:

IF Start THEN
  TimerStar(IN:=Start, PT:=T#10s);
  IF TimerStar.Q THEN
    TimerDelta(IN:=Start, PT:=T#5s);
  END_IF
END_IF

What is the main problem?

medium

A. TimerDelta never starts because IN is tied to Start, not TimerStar.Q

B. TimerStar timer preset time is too short

C. Start input is not used correctly

D. Timers are missing reset logic

Solution

1. Step 1: Check TimerStar input

   TimerStar.IN is correctly tied to Start, so it runs when Start is TRUE.

2. Step 2: Check TimerDelta input

   TimerDelta.IN is tied to Start, not TimerStar.Q. This means TimerDelta starts immediately with Start, not after TimerStar.Q becomes TRUE.

3. Step 3: Identify the problem

   TimerDelta should start only after TimerStar.Q is TRUE to ensure star mode completes before delta starts. Current code starts TimerDelta too early.

4. Final Answer:

   TimerDelta never starts because IN is tied to Start, not TimerStar.Q -> Option A

5. Quick Check:

   TimerDelta.IN must depend on TimerStar.Q [OK]

Hint: TimerDelta.IN should depend on TimerStar.Q, not Start [OK]

Common Mistakes:

• Linking TimerDelta.IN directly to Start
• Ignoring timer sequence dependencies
• Not resetting timers properly

5. You want to design a star-delta starter PLC program where the motor starts in star mode for 8 seconds, then switches to delta mode for 10 seconds, and finally stops. Which timer logic sequence correctly achieves this?

hard

A. Start triggers both TimerStar and TimerDelta simultaneously, motor stops after 18s

B. Start triggers TimerDelta (10s), when TimerDelta.Q is TRUE start TimerStar (8s), then stop motor

C. Start triggers TimerStar (8s), when TimerStar.Q is TRUE start TimerDelta (10s), when TimerDelta.Q is TRUE stop motor

D. Start triggers TimerStar (8s), motor stops immediately after TimerStar.Q is TRUE

Solution

1. Step 1: Understand star-delta timing sequence

   The motor must start in star mode for 8 seconds, then switch to delta mode for 10 seconds, then stop.

2. Step 2: Analyze options

   Start triggers TimerStar (8s), when TimerStar.Q is TRUE start TimerDelta (10s), when TimerDelta.Q is TRUE stop motor correctly sequences timers: TimerStar runs first, then TimerDelta starts after TimerStar.Q is TRUE, then motor stops after TimerDelta.Q is TRUE.

3. Step 3: Eliminate incorrect options

   Start triggers TimerDelta (10s), when TimerDelta.Q is TRUE start TimerStar (8s), then stop motor reverses sequence, Start triggers both TimerStar and TimerDelta simultaneously, motor stops after 18s runs timers simultaneously (wrong), Start triggers TimerStar (8s), motor stops immediately after TimerStar.Q is TRUE stops motor too early.

4. Final Answer:

   Start triggers TimerStar (8s), when TimerStar.Q is TRUE start TimerDelta (10s), when TimerDelta.Q is TRUE stop motor -> Option C

5. Quick Check:

   Sequential timers for star then delta = C [OK]

Hint: Chain timers: star first, then delta, then stop [OK]

Common Mistakes:

• Starting timers simultaneously
• Reversing star and delta order
• Stopping motor too early