Timer preset and accumulated values in PLC Programming

Introduction

Timers help machines wait for a set time before doing something. The preset is the time you want to wait. The accumulated value shows how much time has passed.

Turn on a motor after a delay to avoid sudden starts.

Wait for a safety check before moving a robot arm.

Control how long a light stays on automatically.

Pause a conveyor belt for a set time before restarting.

Syntax

PLC Programming

TIMER_NAME.PRE = preset_time_in_milliseconds
TIMER_NAME.ACC = accumulated_time_in_milliseconds

PRE is the preset time you set for the timer.

ACC shows how much time has passed since the timer started.

Examples

This sets the timer preset to 5 seconds (5000 milliseconds).

PLC Programming

T1.PRE = 5000
// Set timer T1 to 5 seconds

This checks if the timer has reached the preset time.

PLC Programming

IF T1.ACC >= T1.PRE THEN
  // Timer finished
END_IF

Set a 10-second timer and reset the accumulated time to zero.

PLC Programming

T2.PRE = 10000
// Set timer T2 to 10 seconds
T2.ACC = 0
// Reset accumulated time

Sample Program

This program sets a timer for 3 seconds. It simulates the timer running by increasing the accumulated time in steps of 500 milliseconds. It prints if the timer is still running or done.

PLC Programming

// Simple timer example
// Set timer T1 preset to 3 seconds
T1.PRE = 3000

// Simulate timer running by increasing ACC
FOR i = 0 TO 3500 STEP 500 DO
  T1.ACC = i
  IF T1.ACC >= T1.PRE THEN
    PRINT "Timer done at " + STR(T1.ACC) + " ms"
  ELSE
    PRINT "Timer running: " + STR(T1.ACC) + " ms"
  END_IF
END_FOR

Important Notes

The accumulated value resets when the timer stops or is reset.

Preset time is usually set once before starting the timer.

Accumulated value helps check progress during the timer countdown.

Summary

Timers use preset values to know how long to wait.

Accumulated values show how much time has passed.

Use these to control delays and timed actions in automation.

Practice

1. What does the preset value of a timer represent in PLC programming?

easy

A. The number of times the timer has been reset

B. The current time counted by the timer

C. The total time the timer should count before activating

D. The delay before the timer starts counting

Solution

1. Step 1: Understand timer preset meaning

   The preset value is the target time set for the timer to reach before it triggers.

2. Step 2: Differentiate from accumulated value

   The accumulated value shows elapsed time, not the target time.

3. Final Answer:

   The total time the timer should count before activating -> Option C

4. Quick Check:

   Preset = target time [OK]

Hint: Preset is the goal time, accumulated is progress [OK]

Common Mistakes:

• Confusing preset with accumulated value
• Thinking preset changes during timing
• Assuming preset is a delay before start

2. Which of the following is the correct way to set a timer's preset value to 5000 milliseconds in a typical PLC timer instruction?

easy

A. TIMER.PRESET = 5000

B. TIMER.ACC = 5000

C. TIMER.SET = 5000

D. TIMER.TIME = 5000

Solution

1. Step 1: Identify correct property for preset

   In PLC timers, the preset value is usually set with the property named 'PRESET'.

2. Step 2: Check other options

   'ACC' is for accumulated time, 'SET' and 'TIME' are not standard properties for preset.

3. Final Answer:

   TIMER.PRESET = 5000 -> Option A

4. Quick Check:

   Preset set with .PRESET property [OK]

Hint: Preset uses .PRESET, accumulated uses .ACC [OK]

Common Mistakes:

• Using .ACC to set preset
• Using non-standard property names
• Confusing preset with timer start command

3. Given the following timer status after running:
TIMER.PRESET = 10000
TIMER.ACC = 7500
What is the timer's current state?

medium

A. Timer has finished counting and is done

B. Timer is paused at 7500 milliseconds

C. Timer is reset and not started

D. Timer is still counting and not done

Solution

1. Step 1: Compare accumulated and preset values

   The accumulated value (7500) is less than the preset (10000), so the timer has not reached its target.

2. Step 2: Determine timer state

   Since accumulated is less than preset, the timer is still counting and not done.

3. Final Answer:

   Timer is still counting and not done -> Option D

4. Quick Check:

   ACC < PRESET means timer running [OK]

Hint: If ACC < PRESET, timer is running [OK]

Common Mistakes:

• Assuming timer is done when ACC < PRESET
• Confusing paused with running
• Thinking reset means ACC is non-zero

4. A timer's accumulated value never increases even though the timer is enabled. Which is the most likely cause?

medium

A. The preset value is set to zero

B. The timer is not enabled or triggered properly

C. The accumulated value is manually reset continuously

D. The timer's accumulated value is greater than preset

Solution

1. Step 1: Understand timer behavior when enabled

   The accumulated value increases only when the timer is enabled and counting.

2. Step 2: Analyze causes for no increase

   If the timer is not enabled or triggered, the accumulated value stays the same.

3. Final Answer:

   The timer is not enabled or triggered properly -> Option B

4. Quick Check:

   Timer must be enabled to accumulate time [OK]

Hint: Timer must be enabled to increase ACC [OK]

Common Mistakes:

• Assuming preset zero stops accumulation
• Ignoring timer enable condition
• Thinking ACC resets automatically

5. You want a process to run exactly 15 seconds after a start signal. Which timer setup ensures the process starts only after 15 seconds have fully elapsed?

hard

A. Set TIMER.PRESET = 15000 and start process when TIMER.ACC >= TIMER.PRESET

B. Set TIMER.PRESET = 15000 and start process immediately when timer starts

C. Set TIMER.PRESET = 15000 and start process when TIMER.ACC = 0

D. Set TIMER.PRESET = 15000 and start process when TIMER.ACC < TIMER.PRESET

Solution

1. Step 1: Understand timing requirement

   The process must start only after 15 seconds have fully passed.

2. Step 2: Use timer values to control start

   Starting the process when accumulated time is equal or greater than preset ensures 15 seconds elapsed.

3. Final Answer:

   Set TIMER.PRESET = 15000 and start process when TIMER.ACC >= TIMER.PRESET -> Option A

4. Quick Check:

   Start after ACC >= PRESET for exact delay [OK]

Hint: Start process only when ACC reaches preset [OK]

Common Mistakes:

• Starting process immediately on timer start
• Starting before accumulated time reaches preset
• Using ACC = 0 as start condition