Step sequence with timers in PLC Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start the timer when the step is active.

PLC Programming

IF step1_active THEN timer.[1] := TRUE;

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

AEN

BIN

CQ

DPT

Attempts:

3 left

💡 Hint

Common Mistakes

Using PT (preset time) instead of IN to start the timer.

Confusing Q (output) with input signals.

The 'IN' input enables the timer when the step is active.

2fill in blank

medium

Complete the code to check if the timer has finished.

PLC Programming

IF timer.[1] THEN next_step := TRUE;

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

AIN

BET

CQ

DPT

Attempts:

3 left

💡 Hint

Common Mistakes

Using ET (elapsed time) instead of Q to check completion.

Checking PT (preset time) which is a constant.

The 'Q' output becomes TRUE when the timer finishes.

3fill in blank

hard

Fix the error in the timer reset code.

PLC Programming

IF step2_active THEN timer.[1] := FALSE;

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

AET

BQ

CRESET

DIN

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to reset the timer by setting Q or ET.

Using a non-existent RESET input.

Setting 'IN' to FALSE resets the timer by disabling it.

4fill in blank

hard

Fill both blanks to create a step sequence with timer control.

PLC Programming

IF step1_active THEN timer.[1] := TRUE; IF timer.[2] THEN step2_active := TRUE;

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

AIN

BQ

CET

DPT

Attempts:

3 left

💡 Hint

Common Mistakes

Using ET instead of Q to check timer done.

Confusing PT (preset time) with timer signals.

Enable timer with IN and check completion with Q to move to next step.

5fill in blank

hard

Fill all three blanks to define a timer-based step transition.

PLC Programming

timer[1].[2] := T#5s; IF timer[3].Q THEN step1_active := FALSE;

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

AT1

BPT

DET

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing timer instance names.

Using ET instead of Q to check timer completion.

Set preset time PT on timer T1 and check Q output to end step.

Practice

1. What is the main purpose of using timers in a step sequence in PLC programming?

easy

A. To wait a set time before moving to the next step

B. To immediately jump to the last step

C. To reset the entire program

D. To skip steps randomly

Solution

1. Step 1: Understand the role of timers in step sequences

   Timers are used to create delays between steps, ensuring each step runs for a set time.

2. Step 2: Identify the correct timer function

   The timer waits before allowing the sequence to move to the next step, controlling timing precisely.

3. Final Answer:

   To wait a set time before moving to the next step -> Option A

4. Quick Check:

   Timers delay steps = A [OK]

Hint: Timers pause steps to control sequence timing [OK]

Common Mistakes:

• Thinking timers skip steps
• Assuming timers reset the program
• Believing timers jump to last step

2. Which of the following is the correct way to start a timer in a PLC step sequence?

easy

A. StartTimer(T1, 5s)

B. TimerStart T1 5

C. TON T1, 5s

D. T1 = Timer(5)

Solution

1. Step 1: Recognize standard PLC timer syntax

   In many PLC languages, the TON (Timer ON Delay) instruction is used with a timer name and preset time.

2. Step 2: Compare options to standard syntax

   TON T1, 5s uses 'TON T1, 5s' which matches common PLC timer start syntax.

3. Final Answer:

   TON T1, 5s -> Option C

4. Quick Check:

   TON is standard timer start = C [OK]

Hint: Look for TON keyword to start timers [OK]

Common Mistakes:

• Using incorrect function names
• Missing TON keyword
• Wrong timer parameter format

3. Given this step sequence code snippet:

Step 1: Start TON timer T1 for 3 seconds
Step 2: When T1 done, move to Step 2 and start TON timer T2 for 2 seconds
Step 3: When T2 done, move to Step 3

What is the total time before Step 3 starts?

medium

A. 5 seconds

B. 2 seconds

C. 3 seconds

D. Cannot be determined

Solution

1. Step 1: Add timer durations sequentially

   Step 1 waits 3 seconds, then Step 2 waits 2 seconds before Step 3.

2. Step 2: Calculate total wait time

   Total time = 3 seconds + 2 seconds = 5 seconds.

3. Final Answer:

   5 seconds -> Option A

4. Quick Check:

   3s + 2s = 5s total [OK]

Hint: Add timer durations in sequence for total delay [OK]

Common Mistakes:

• Only counting one timer duration
• Confusing timer start with timer done
• Assuming timers run in parallel

4. You have a step sequence with timers but the sequence moves to the next step immediately without waiting. What is the most likely error?

medium

A. Timer is counting up correctly

B. Timer preset value is set to zero

C. Step sequence is missing

D. PLC power is off

Solution

1. Step 1: Identify why timer causes no delay

   If the timer preset is zero, it finishes instantly, causing no wait.

2. Step 2: Check other options

   Counting up correctly means timer works; missing sequence or power off would stop all operation.

3. Final Answer:

   Timer preset value is set to zero -> Option B

4. Quick Check:

   Zero preset = no delay [OK]

Hint: Check timer preset is not zero for delay [OK]

Common Mistakes:

• Ignoring timer preset value
• Assuming power off causes immediate step
• Confusing timer counting with preset

5. You want a step sequence that:
1. Starts motor for 4 seconds,
2. Waits 3 seconds with motor off,
3. Then starts motor again.

Which timer setup correctly implements this sequence?

hard

A. Step 1: TON T1, 4s; Step 2: TON T2, 3s; Step 3: Motor ON

B. Step 1: Motor ON; Step 2: TON T1, 4s; Step 3: TON T2, 3s; Step 4: Motor ON

C. Step 1: TON T1, 3s; Step 2: Motor ON; Step 3: TON T2, 4s

D. Step 1: Motor ON and TON T1, 4s; Step 2: Motor OFF and TON T2, 3s; Step 3: Motor ON

Solution

1. Step 1: Match motor state with timers per step

   Step 1 must run motor ON while timer T1 counts 4 seconds; Step 2 motor OFF with timer T2 for 3 seconds; Step 3 motor ON again.

2. Step 2: Verify options

   Only Step 1: Motor ON and TON T1, 4s; Step 2: Motor OFF and TON T2, 3s; Step 3: Motor ON correctly pairs motor ON/OFF states with timers in the right steps.

3. Final Answer:

   Step 1: Motor ON and TON T1, 4s; Step 2: Motor OFF and TON T2, 3s; Step 3: Motor ON -> Option D

4. Quick Check:

   Motor state matches timers per step = D [OK]

Hint: Pair motor ON/OFF with timers in each step [OK]

Common Mistakes:

• Not turning motor OFF during wait
• Mixing timer durations
• Skipping motor control in steps