Comparison instructions (EQ, NE, GT, LT) in PLC Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if input A equals input B.

PLC Programming

IF A [1] B THEN
  OUTPUT := TRUE;
END_IF;

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

ANE

BEQ

CGT

DLT

Attempts:

3 left

💡 Hint

Common Mistakes

Using NE instead of EQ will check for not equal.

Using GT or LT checks greater or less, not equality.

The EQ instruction checks if two values are equal.

2fill in blank

medium

Complete the code to check if sensor value is greater than threshold.

PLC Programming

IF SensorValue [1] Threshold THEN
  Alarm := TRUE;
END_IF;

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

AGT

BEQ

CNE

DLT

Attempts:

3 left

💡 Hint

Common Mistakes

Using LT will check if SensorValue is less than Threshold.

Using EQ checks equality, not greater than.

GT means greater than, so it checks if SensorValue is above Threshold.

3fill in blank

hard

Fix the error in the code to check if counter is not equal to max value.

PLC Programming

IF Counter [1] MaxValue THEN
  Reset := TRUE;
END_IF;

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

AEQ

BGT

CNE

DLT

Attempts:

3 left

💡 Hint

Common Mistakes

Using EQ will check if Counter equals MaxValue, which is opposite.

Using GT or LT checks greater or less, not inequality.

NE means not equal, so it correctly checks if Counter is different from MaxValue.

4fill in blank

hard

Fill both blanks to check if temperature is less than limit and pressure is not equal to zero.

PLC Programming

IF Temperature [1] Limit AND Pressure [2] 0 THEN
  Warning := TRUE;
END_IF;

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

ALT

BEQ

CNE

DGT

Attempts:

3 left

💡 Hint

Common Mistakes

Using EQ instead of NE for Pressure will check equality, not inequality.

Using GT instead of LT for Temperature will check greater than, not less.

LT checks if Temperature is less than Limit, NE checks if Pressure is not equal to zero.

5fill in blank

hard

Fill all three blanks to create a condition: speed greater than minSpeed, speed less than maxSpeed, and status not equal to errorCode.

PLC Programming

IF Speed [1] minSpeed AND Speed [2] maxSpeed AND Status [3] errorCode THEN
  Run := TRUE;
END_IF;

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

AEQ

BLT

CNE

DGT

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up GT and LT operators.

Using EQ instead of NE for status check.

GT checks Speed > minSpeed, LT checks Speed < maxSpeed, NE checks Status != errorCode.

Practice

1. Which comparison instruction checks if two values are exactly the same in PLC programming?

easy

A. EQ

B. NE

C. GT

D. LT

Solution

1. Step 1: Understand the meaning of EQ

   EQ stands for 'equal' and checks if two values are exactly the same.

2. Step 2: Compare with other instructions

   NE means not equal, GT means greater than, and LT means less than, so they do not check equality.

3. Final Answer:

   EQ -> Option A

4. Quick Check:

   EQ means equal [OK]

Hint: EQ means equal, so it checks if values match exactly [OK]

Common Mistakes:

• Confusing EQ with NE
• Thinking GT checks equality
• Mixing LT with EQ

2. Which of the following is the correct syntax to check if variable A is greater than variable B in a PLC program?

easy

A. IF A LT B THEN

B. IF A NE B THEN

C. IF A EQ B THEN

D. IF A GT B THEN

Solution

1. Step 1: Identify the comparison for 'greater than'

   GT means 'greater than', so to check if A is greater than B, use 'A GT B'.

2. Step 2: Check other options

   LT means less than, EQ means equal, NE means not equal, so they are incorrect for this check.

3. Final Answer:

   IF A GT B THEN -> Option D

4. Quick Check:

   GT means greater than [OK]

Hint: GT means greater than, so use it to compare if A > B [OK]

Common Mistakes:

• Using LT instead of GT
• Confusing EQ with GT
• Using NE for greater than check

3. Given the following PLC code snippet:

VAR
  X: INT := 5;
  Y: INT := 10;
  Result: BOOL;
END_VAR

Result := X LT Y;

What will be the value of Result after execution?

medium

A. Syntax Error

B. FALSE

C. TRUE

D. Undefined

Solution

1. Step 1: Understand the comparison LT

   LT means 'less than'. The code checks if X (5) is less than Y (10).

2. Step 2: Evaluate the condition

   Since 5 is less than 10, the condition is true, so Result will be TRUE.

3. Final Answer:

   TRUE -> Option C

4. Quick Check:

   5 LT 10 = TRUE [OK]

Hint: LT means less than; 5 < 10 is true [OK]

Common Mistakes:

• Thinking LT means greater than
• Assuming Result is FALSE
• Confusing syntax with error

4. Identify the error in this PLC comparison instruction:

IF A NEQ B THEN
  // do something
END_IF

medium

A. Missing THEN keyword

B. NEQ is not a valid comparison instruction

C. Comparison should be EQ instead of NEQ

D. IF statement missing parentheses

Solution

1. Step 1: Check the comparison instruction used

   The code uses 'NEQ' which is not a standard PLC comparison instruction.

2. Step 2: Identify correct instruction

   The correct instruction for 'not equal' is 'NE', not 'NEQ'.

3. Final Answer:

   NEQ is not a valid comparison instruction -> Option B

4. Quick Check:

   Use NE for not equal, not NEQ [OK]

Hint: Use NE for not equal, not NEQ [OK]

Common Mistakes:

• Using NEQ instead of NE
• Forgetting THEN keyword
• Adding unnecessary parentheses

5. You want to write a PLC program that turns on a motor only if the temperature is greater than 50 and the pressure is less than 100. Which combination of comparison instructions correctly checks this condition?

hard

A. IF Temperature GT 50 AND Pressure LT 100 THEN Motor := TRUE;

B. IF Temperature LT 50 OR Pressure GT 100 THEN Motor := TRUE;

C. IF Temperature EQ 50 AND Pressure EQ 100 THEN Motor := TRUE;

D. IF Temperature NE 50 AND Pressure NE 100 THEN Motor := TRUE;

Solution

1. Step 1: Translate the condition into comparisons

   The motor should turn on if temperature is greater than 50 (GT 50) and pressure is less than 100 (LT 100).

2. Step 2: Check each option

   IF Temperature GT 50 AND Pressure LT 100 THEN Motor := TRUE; uses GT and LT with AND, matching the condition exactly. Other options use wrong comparisons or OR instead of AND.

3. Final Answer:

   IF Temperature GT 50 AND Pressure LT 100 THEN Motor := TRUE; -> Option A

4. Quick Check:

   GT and LT with AND matches condition [OK]

Hint: Use GT for greater, LT for less, combine with AND for both conditions [OK]

Common Mistakes:

• Using OR instead of AND
• Using EQ instead of GT or LT
• Mixing NE with equality checks