Parts counter with conveyor in PLC Programming - Step-by-Step Execution

Concept Flow - Parts counter with conveyor

Start Conveyor

↓

Detect Part Sensor

↓

Is Part Detected?

No→Keep Conveyor Running

Yes↓

Increment Part Counter

↓

Check Counter Limit

Yes No↓

Stop Conveyor

↓

End

The conveyor runs and checks a sensor for parts. When a part is detected, the counter increases. If the counter reaches a limit, the conveyor stops.

Execution Sample

PLC Programming

conveyor = True
counter = 0
limit = 3
sensor = [False, True, True, False, True]
for detected in sensor:
    if detected:
        counter += 1
        if counter >= limit:
            conveyor = False

This code simulates a conveyor detecting parts and counting them up to a limit.

Execution Table

Step	Sensor Reading	Part Detected?	Counter Before	Action	Counter After	Conveyor State
1	False	No	0	Keep conveyor running	0	Running
2	True	Yes	0	Increment counter	1	Running
3	True	Yes	1	Increment counter	2	Running
4	False	No	2	Keep conveyor running	2	Running
5	True	Yes	2	Increment counter	3	Stopped

💡 Counter reached limit 3, conveyor stops

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	Final
counter	0	0	1	2	2	3	3
conveyor	Running	Running	Running	Running	Running	Stopped	Stopped

Key Moments - 2 Insights

Why does the conveyor stop only after the third detected part?

Because the counter increments only when a part is detected (see steps 2,3,5 in execution_table). When counter reaches the limit 3 at step 5, the conveyor stops.

What happens when the sensor reads False?

No part is detected, so the counter does not increase and the conveyor keeps running (see steps 1 and 4).

Visual Quiz - 3 Questions

Look at the execution table, what is the counter value after step 3?

A 3

B 2

C 1

D 0

💡 Hint

Check the 'Counter After' column at step 3 in the execution_table.

At which step does the conveyor stop running?

A Step 4

B Step 3

C Step 5

D Step 2

💡 Hint

Look at the 'Conveyor State' column in the execution_table.

If the limit was set to 2, at which step would the conveyor stop?

A Step 3

B Step 4

C Step 5

D Step 2

💡 Hint

Check when the counter reaches 2 in the variable_tracker and execution_table.

Concept Snapshot

Parts counter with conveyor:
- Conveyor runs and sensor detects parts
- Each detected part increments counter
- When counter reaches limit, conveyor stops
- Sensor False means no increment
- Simple loop with condition and counter

Full Transcript

This example shows a parts counter with a conveyor system. The conveyor runs continuously and a sensor detects parts passing by. Each time the sensor detects a part, the counter increases by one. When the counter reaches a set limit, the conveyor stops automatically. If the sensor does not detect a part, the conveyor keeps running and the counter stays the same. This logic helps automate counting parts on a conveyor belt and stopping when a target is reached.

Practice

1. What is the main purpose of a parts counter in a conveyor system?

easy

A. To count the number of parts passing a sensor and stop the conveyor after a set count

B. To increase the speed of the conveyor belt automatically

C. To sort parts by size on the conveyor

D. To clean the conveyor belt during operation

Solution

1. Step 1: Understand the role of the parts counter

   The parts counter uses a sensor to detect each part passing on the conveyor.

2. Step 2: Identify the action after counting

   Once the set number of parts is reached, the conveyor stops to control production.

3. Final Answer:

   To count the number of parts passing a sensor and stop the conveyor after a set count -> Option A

4. Quick Check:

   Parts counter purpose = Count and stop conveyor [OK]

Hint: Focus on counting and stopping conveyor after set parts [OK]

Common Mistakes:

• Confusing counting with sorting
• Thinking the counter speeds up conveyor
• Assuming it cleans the conveyor

2. Which of the following is the correct way to reset a parts counter in a PLC program?

easy

A. Disconnect the sensor from the PLC

B. Increase the counter value by one

C. Stop the conveyor without changing the counter

D. Set the counter value to zero using a reset instruction

Solution

1. Step 1: Identify how counters reset in PLCs

   Counters are reset by setting their value back to zero using a reset instruction.

2. Step 2: Eliminate incorrect options

   Increasing the counter or stopping conveyor does not reset the count; disconnecting sensor stops detection but not reset.

3. Final Answer:

   Set the counter value to zero using a reset instruction -> Option D

4. Quick Check:

   Reset counter = set to zero [OK]

Hint: Reset means setting count back to zero, not stopping conveyor [OK]

Common Mistakes:

• Confusing reset with increment
• Stopping conveyor does not reset count
• Disconnecting sensor is not a reset

3. Given this PLC ladder logic snippet for a parts counter:

IF Sensor = TRUE THEN
  Counter = Counter + 1
END IF
IF Counter >= 10 THEN
  Conveyor = OFF
END IF

What will be the state of the conveyor after 10 parts pass the sensor?

medium

A. Conveyor remains ON

B. Sensor stops detecting parts

C. Conveyor turns OFF

D. Counter resets to zero

Solution

1. Step 1: Analyze the counter increment

   Each time the sensor is TRUE, the counter increases by 1 until it reaches 10.

2. Step 2: Check conveyor control condition

   When counter is 10 or more, the conveyor is turned OFF.

3. Final Answer:

   Conveyor turns OFF -> Option C

4. Quick Check:

   Counter >= 10 stops conveyor [OK]

Hint: Conveyor stops when count reaches or exceeds limit [OK]

Common Mistakes:

• Thinking conveyor stays ON after 10 parts
• Assuming counter resets automatically
• Believing sensor stops detecting

4. Identify the error in this PLC code snippet for counting parts:

IF Sensor = TRUE THEN
  Counter = Counter + 1
END IF
IF Counter = 10 THEN
  Conveyor = OFF
  Counter = 0
END IF

What problem might occur?

medium

A. Counter resets before conveyor stops, so conveyor never stops

B. Counter never increments because sensor is not checked

C. Conveyor never turns OFF because condition uses '=' instead of '>='

D. Sensor input is not used in the code

Solution

1. Step 1: Review counter reset timing

   The counter resets to zero immediately after reaching 10, possibly before conveyor stops.

2. Step 2: Understand effect on conveyor

   If counter resets too soon, the conveyor OFF condition may not hold, causing conveyor to continue running.

3. Final Answer:

   Counter resets before conveyor stops, so conveyor never stops -> Option A

4. Quick Check:

   Resetting counter too early breaks stop logic [OK]

Hint: Reset counter after conveyor stops, not before [OK]

Common Mistakes:

• Resetting counter immediately after reaching target
• Using '=' instead of '>=' causing missed conditions
• Ignoring sensor input usage

5. You want to modify a parts counter program so the conveyor stops only after counting 50 parts, but also resets the counter automatically after stopping. Which sequence of actions in the PLC program is correct?

hard

A. Reset counter, then check if counter >= 50, then stop conveyor

B. Check if counter >= 50, then stop conveyor, then reset counter

C. Stop conveyor first, then check counter, then reset counter

D. Increment counter only after conveyor stops

Solution

1. Step 1: Set condition to check counter value

   The program must check if the counter has reached or exceeded 50 parts.

2. Step 2: Stop conveyor and then reset counter

   After stopping the conveyor, reset the counter to zero to prepare for next batch.

3. Final Answer:

   Check if counter >= 50, then stop conveyor, then reset counter -> Option B

4. Quick Check:

   Stop then reset after count reached [OK]

Hint: Stop conveyor first, then reset counter after count reached [OK]

Common Mistakes:

• Resetting counter before checking count
• Stopping conveyor without checking count
• Incrementing counter only after stopping conveyor