Data conversion instructions in PLC Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

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

Data conversion instructions change data from one type to another, like from integer to real number, so the PLC can process it correctly.

beginner

Name a common data conversion instruction in PLC programming and its function.

The INT_TO_REAL instruction converts an integer value to a real (floating-point) number.

intermediate

Why should you be careful when converting data types in PLCs?

Because converting data incorrectly can cause loss of information or unexpected behavior, like truncating decimals or overflow errors.

beginner

How does the BOOL_TO_INT instruction work in PLC programming?

It converts a Boolean value (TRUE or FALSE) into an integer, usually 1 for TRUE and 0 for FALSE.

intermediate

What happens if you convert a large REAL number to an INT in a PLC?

The decimal part is dropped, and if the number is too large, it may cause overflow or incorrect values.

Which instruction converts an integer to a real number in PLC programming?

A INT_TO_REAL

B REAL_TO_INT

C BOOL_TO_INT

D STRING_TO_INT

INT_TO_REAL converts integer values to real numbers.

What value does BOOL_TO_INT return for TRUE?

A 0

B TRUE

C -1

D 1

BOOL_TO_INT returns 1 for TRUE and 0 for FALSE.

What risk exists when converting REAL to INT in PLCs?

A Decimal truncation

B Data duplication

C Boolean conversion

D String overflow

REAL to INT conversion drops the decimal part, causing truncation.

Which instruction would you use to convert a string to an integer?

A INT_TO_STRING

B STRING_TO_INT

C REAL_TO_INT

D BOOL_TO_INT

STRING_TO_INT converts string data to integer values.

Why is data conversion important in PLC programming?

A To increase memory size

B To speed up the PLC clock

C To change data types for correct processing

D To create new variables

Data conversion ensures data is in the right type for processing.

Explain how data conversion instructions help in PLC programming and give two examples.

Think about changing data types so PLC can work with different kinds of data.

Describe potential problems when converting data types in PLCs and how to avoid them.

Consider what happens if you convert a big number or a decimal to an integer.

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