Scaling analog values in PLC Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to scale the input value from 0-10V to 0-100 units.

PLC Programming

scaled_value = (input_voltage [1] 10) * 100

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

A*

B/

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using multiplication instead of division causes incorrect scaling.

Adding or subtracting the voltage does not normalize the value.

We divide the input voltage by 10 to normalize it between 0 and 1 before scaling.

2fill in blank

medium

Complete the code to convert a raw sensor value (0-4095) to a temperature in Celsius (0-100°C).

PLC Programming

temperature_c = (raw_value [1] 4095) * 100

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

A/

B*

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Multiplying raw_value by 4095 causes wrong results.

Adding or subtracting raw_value does not scale properly.

Dividing the raw value by 4095 normalizes it before scaling to temperature.

3fill in blank

hard

Fix the error in the scaling formula to convert a 4-20mA signal to 0-100 units.

PLC Programming

scaled_units = ((current_mA [1] 4) / 16) * 100

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

A/

B+

C*

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Adding 4 instead of subtracting causes wrong offset.

Multiplying or dividing by 4 instead of subtracting causes errors.

Subtract 4mA to zero the signal before scaling by the 16mA span.

4fill in blank

hard

Fill both blanks to scale a sensor value from 100-500 to 0-200 units.

PLC Programming

scaled_value = ((sensor_value [1] 100) * 200) / [2]

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

A-

B+

C400

D100

Attempts:

3 left

💡 Hint

Common Mistakes

Adding 100 instead of subtracting causes wrong offset.

Dividing by 100 instead of 400 causes incorrect scaling.

Subtract 100 to zero the input range, then divide by 400 (500-100) to normalize before scaling.

5fill in blank

hard

Fill all three blanks to create a dictionary mapping sensor names to scaled values above 50.

PLC Programming

scaled_sensors = { [1]: [2] for [3], val in sensors.items() if val > 50 }

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

Aname

Bval * 2

Dsensor

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names causes errors.

Not scaling the value properly results in wrong output.

Use 'name' as key, scale value by multiplying by 2, and iterate with 'name' as variable.

Practice

1. What is the main purpose of scaling analog values in PLC programming?

easy

A. To reduce the size of the PLC program

B. To increase the speed of the PLC processor

C. To convert raw sensor signals into meaningful engineering units

D. To change digital signals into analog signals

Solution

1. Step 1: Understand analog input signals

   Raw sensor signals are usually voltage or current values that need interpretation.

2. Step 2: Purpose of scaling

   Scaling converts these raw signals into meaningful units like temperature or pressure.

3. Final Answer:

   To convert raw sensor signals into meaningful engineering units -> Option C

4. Quick Check:

   Scaling = Convert raw to useful units [OK]

Hint: Scaling means converting raw sensor data to real-world units [OK]

Common Mistakes:

• Confusing scaling with speeding up the PLC
• Thinking scaling reduces program size
• Mixing analog and digital signal conversion

2. Which of the following is the correct formula to scale a raw analog input raw from range raw_min to raw_max into a scaled output range scale_min to scale_max?

easy

A. scaled = (raw - raw_min) * (scale_max - scale_min) / (raw_max - raw_min) + scale_min

B. scaled = raw * (scale_max - scale_min) / (raw_max + raw_min) + scale_min

C. scaled = (raw + raw_min) * (scale_max + scale_min) / (raw_max - raw_min)

D. scaled = (raw - raw_max) * (scale_min - scale_max) / (raw_min - raw_max) + scale_max

Solution

1. Step 1: Recall the scaling formula

   The formula maps raw input linearly to the scaled range using subtraction and division.

2. Step 2: Check each formula

   scaled = (raw - raw_min) * (scale_max - scale_min) / (raw_max - raw_min) + scale_min correctly subtracts raw_min, scales by ratio of output to input range, then adds scale_min.

3. Final Answer:

   scaled = (raw - raw_min) * (scale_max - scale_min) / (raw_max - raw_min) + scale_min -> Option A

4. Quick Check:

   Scaling formula = scaled = (raw - raw_min) * (scale_max - scale_min) / (raw_max - raw_min) + scale_min [OK]

Hint: Use (raw - raw_min) * output_range / input_range + scale_min [OK]

Common Mistakes:

• Adding raw_min instead of subtracting
• Using addition instead of subtraction in denominator
• Mixing max and min values incorrectly

3. Given a raw input value of 2500 from a sensor with raw range 0-4095, scaled to temperature range 0-100°C using the formula scaled = (raw - 0) * (100 - 0) / (4095 - 0) + 0, what is the scaled temperature?

medium

A. 61.07°C

B. 25.00°C

C. 100.00°C

D. 0.61°C

Solution

1. Step 1: Substitute values into formula

   scaled = (2500 - 0) * (100 - 0) / (4095 - 0) + 0 = 2500 * 100 / 4095

2. Step 2: Calculate the scaled value

   scaled = 250000 / 4095 ≈ 61.07°C

3. Final Answer:

   61.07°C -> Option A

4. Quick Check:

   2500/4095 ≈ 0.61 * 100 = 61.07 [OK]

Hint: Divide raw by max raw, multiply by max scale [OK]

Common Mistakes:

• Using raw_max as 2500 instead of 4095
• Forgetting to subtract raw_min
• Mixing up numerator and denominator

4. A PLC program uses this scaling code snippet:

scaled = (raw - 100) * (200 - 0) / (1000 - 0) + 0

What is the error in this scaling formula?

medium

A. The raw_min value should be 0, not 100

B. The denominator should be (1000 - 100) instead of (1000 - 0)

C. The formula should subtract scale_min, not raw_min

D. The scale_max value should be 100, not 200

Solution

1. Step 1: Identify raw input range

   Raw input minimum is 100, maximum is 1000, so input range is 1000 - 100 = 900.

2. Step 2: Check denominator in formula

   The formula uses (1000 - 0) = 1000, which is incorrect; it should be (1000 - 100) = 900.

3. Final Answer:

   The denominator should be (1000 - 100) instead of (1000 - 0) -> Option B

4. Quick Check:

   Input range = max - min = 900, not 1000 [OK]

Hint: Denominator = raw_max - raw_min, not raw_max - 0 [OK]

Common Mistakes:

• Using wrong input range denominator
• Confusing scale and raw min/max
• Subtracting scale_min instead of adding

5. You have a sensor outputting raw values from 500 to 3500 representing pressure from 20 to 100 psi. Which formula correctly scales a raw input raw to pressure?

hard

A. pressure = (raw - 500) * (100 - 20) / (3500 - 500) + 0

B. pressure = (raw - 0) * (100 - 20) / (3500 - 500) + 20

C. pressure = (raw - 500) * (100 - 20) / (3500 - 0) + 20

D. pressure = (raw - 500) * (100 - 20) / (3500 - 500) + 20

Solution

1. Step 1: Identify raw and scale ranges

   Raw range: 500 to 3500; pressure range: 20 to 100 psi.

2. Step 2: Apply scaling formula

   Use (raw - raw_min) * (scale_max - scale_min) / (raw_max - raw_min) + scale_min.

3. Step 3: Check each option

   pressure = (raw - 500) * (100 - 20) / (3500 - 500) + 20 correctly uses raw_min=500, raw_max=3500, scale_min=20, scale_max=100.

4. Final Answer:

   pressure = (raw - 500) * (100 - 20) / (3500 - 500) + 20 -> Option D

5. Quick Check:

   Correct raw and scale min/max used in formula [OK]

Hint: Always subtract raw_min and add scale_min in formula [OK]

Common Mistakes:

• Using 0 instead of raw_min in subtraction
• Adding 0 instead of scale_min at end
• Mixing raw_max with 0 in denominator