Data conversion instructions in PLC Programming - Step-by-Step Execution

Concept Flow - Data conversion instructions

Start

↓

Input Data

↓

Select Conversion Instruction

↓

Execute Conversion

↓

Output Converted Data

↓

End

The flow shows how data is taken as input, a conversion instruction is selected and executed, then the converted data is output.

Execution Sample

PLC Programming

INT_VAR := 123;
REAL_VAR := INT_TO_REAL(INT_VAR);
BOOL_VAR := REAL_TO_BOOL(REAL_VAR);

This code converts an integer to a real number, then converts that real number to a boolean.

Execution Table

Step	Instruction	Input Value	Conversion Result	Output Variable
1	INT_TO_REAL	INT_VAR = 123	123.0	REAL_VAR
2	REAL_TO_BOOL	REAL_VAR = 123.0	TRUE	BOOL_VAR
3	End	-	-	-

💡 All conversions executed; program ends.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
INT_VAR	undefined	123	123	123
REAL_VAR	undefined	123.0	123.0	123.0
BOOL_VAR	undefined	undefined	TRUE	TRUE

Key Moments - 2 Insights

Why does converting a real number to boolean result in TRUE?

Because any non-zero real number converts to TRUE in REAL_TO_BOOL, as shown in step 2 of the execution_table.

What happens if the integer value is zero when converting to boolean?

If the integer is zero, after conversion to real and then boolean, the boolean will be FALSE, since zero converts to FALSE.

Visual Quiz - 3 Questions

Look at the execution_table at step 1, what is the value of REAL_VAR after conversion?

A 123

B 123.0

C TRUE

D 0

💡 Hint

Check the Conversion Result column at step 1 in execution_table.

At which step does BOOL_VAR get its value assigned?

A Step 2

B Step 3

C Step 1

D Before Step 1

💡 Hint

Look at the Output Variable column in execution_table to see when BOOL_VAR is assigned.

If INT_VAR was 0, what would BOOL_VAR be after step 2?

A TRUE

B 123.0

C FALSE

D undefined

💡 Hint

Recall that zero converts to FALSE in boolean conversion as explained in key_moments.

Concept Snapshot

Data conversion instructions change data types in PLCs.
Common conversions: INT_TO_REAL, REAL_TO_BOOL.
Non-zero values convert to TRUE; zero converts to FALSE.
Use conversion instructions to match data types for operations.

Full Transcript

This lesson shows how data conversion instructions work in PLC programming. We start with an integer variable set to 123. Then we convert it to a real number using INT_TO_REAL, resulting in 123.0. Next, we convert that real number to a boolean using REAL_TO_BOOL, which results in TRUE because the number is non-zero. Variables change values step by step as shown in the variable tracker. Key points include understanding that zero converts to FALSE and non-zero to TRUE in boolean conversions. The execution table traces each step clearly. This helps beginners see how data changes type and value in a PLC program.

Practice

1. What is the main purpose of data conversion instructions in PLC programming?

easy

A. To create new variables automatically

B. To speed up the PLC scan time

C. To change data types so PLCs can process them correctly

D. To reset the PLC program

Solution

1. Step 1: Understand data conversion instructions

   Data conversion instructions change one data type to another so the PLC can handle the data properly.

2. Step 2: Identify the main purpose

   The main goal is to ensure data compatibility during processing or display.

3. Final Answer:

   To change data types so PLCs can process them correctly -> Option C

4. Quick Check:

   Data conversion = change data types [OK]

Hint: Data conversion = changing data types for compatibility [OK]

Common Mistakes:

• Thinking it speeds up the PLC scan
• Confusing with variable creation
• Assuming it resets the program

2. Which of the following is the correct syntax to convert an integer to a real number in a typical PLC program?

easy

A. INT_TO_REAL(value)

B. REAL(value)

C. TO_REAL(value)

D. CONVERT_REAL(value)

Solution

1. Step 1: Recall standard PLC conversion functions

   Most PLCs use functions like INT_TO_REAL to convert integers to real numbers.

2. Step 2: Match syntax options

   INT_TO_REAL(value) is the standard and correct syntax for this conversion.

3. Final Answer:

   INT_TO_REAL(value) -> Option A

4. Quick Check:

   Integer to real = INT_TO_REAL() [OK]

Hint: Look for function names starting with source type + _TO_ + target type [OK]

Common Mistakes:

• Using generic names like REAL(value)
• Assuming TO_REAL is standard
• Using CONVERT_REAL which is not typical

3. Given the following PLC code snippet:

INT_VAR := 1234;
REAL_VAR := INT_TO_REAL(INT_VAR);
INT_CONV := REAL_TO_INT(REAL_VAR);

What is the value of INT_CONV after execution?

medium

A. 1235

B. 1234

C. 1233

D. 0

Solution

1. Step 1: Convert INT_VAR to REAL_VAR

   INT_VAR is 1234, converted to real: REAL_VAR = 1234.0 (no change in value, just type).

2. Step 2: Convert REAL_VAR back to INT_CONV

   REAL_TO_INT(1234.0) converts back to integer 1234 without loss.

3. Final Answer:

   1234 -> Option B

4. Quick Check:

   Conversion back and forth keeps value same [OK]

Hint: Converting int to real and back keeps original integer value [OK]

Common Mistakes:

• Assuming rounding changes value
• Thinking conversion truncates incorrectly
• Confusing data types with values

4. Identify the error in this PLC code snippet:

REAL_VAR := 12.7;
INT_VAR := REAL_TO_INT(REAL_VAR);
BOOL_VAR := INT_TO_BOOL(REAL_VAR);

medium

A. REAL_VAR should be integer type

B. REAL_TO_INT cannot convert real to int

C. Missing semicolon after first line

D. INT_TO_BOOL cannot convert REAL directly

Solution

1. Step 1: Check each conversion

   REAL_TO_INT(REAL_VAR) is valid to convert real to int.

2. Step 2: Check INT_TO_BOOL(REAL_VAR)

   INT_TO_BOOL expects an integer input, but REAL_VAR is real type, causing an error.

3. Final Answer:

   INT_TO_BOOL cannot convert REAL directly -> Option D

4. Quick Check:

   Conversion functions require correct input types [OK]

Hint: Check input type matches conversion function parameter [OK]

Common Mistakes:

• Assuming all conversions accept any type
• Ignoring type mismatch errors
• Thinking missing semicolon causes conversion error

5. You have a PLC program that reads a sensor value as a 16-bit integer but needs to display it as a floating-point number with two decimal places. Which sequence of data conversion instructions is best to achieve this?

hard

A. INT_TO_REAL(sensor_value) then multiply by 0.01

B. REAL_TO_INT(sensor_value) then divide by 100

C. INT_TO_BOOL(sensor_value) then convert to REAL

D. BOOL_TO_INT(sensor_value) then multiply by 100

Solution

1. Step 1: Convert integer sensor value to real

   Use INT_TO_REAL to convert the 16-bit integer to a floating-point number.

2. Step 2: Adjust scale for decimal places

   Multiply the real number by 0.01 to shift decimal two places for display.

3. Final Answer:

   INT_TO_REAL(sensor_value) then multiply by 0.01 -> Option A

4. Quick Check:

   Convert int to real, then scale for decimals [OK]

Hint: Convert int to real first, then scale for decimals [OK]

Common Mistakes:

• Trying to convert real to int first
• Using boolean conversions incorrectly
• Multiplying before converting data type