Series logic (AND condition) in PLC Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if both inputs are ON using AND logic.

PLC Programming

if input1 [1] input2 then
  output = ON
end if

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

AXOR

BAND

CNOT

DOR

Attempts:

3 left

💡 Hint

Common Mistakes

Using OR instead of AND will turn output ON if either input is ON.

Using NOT or XOR will not check both inputs correctly.

The AND operator ensures both input1 and input2 must be ON for the output to be ON.

2fill in blank

medium

Complete the code to turn ON the motor only if sensor1 and sensor2 are both active.

PLC Programming

if sensor1 [1] sensor2 then
  motor = ON
else
  motor = OFF
end if

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

AAND

BNOR

CXOR

DOR

Attempts:

3 left

💡 Hint

Common Mistakes

Using OR will run the motor if any sensor is active, not both.

XOR and NOR do not represent simple AND logic.

Using AND ensures the motor runs only when both sensors are active.

3fill in blank

hard

Fix the error in the code to correctly implement series logic with two switches.

PLC Programming

if switch1 [1] switch2 then
  light = ON
end if

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

AOR

BNOT

CAND

DXOR

Attempts:

3 left

💡 Hint

Common Mistakes

Using OR will turn the light ON if either switch is ON.

NOT and XOR do not represent series logic.

AND is needed to ensure the light turns ON only when both switches are ON.

4fill in blank

hard

Fill both blanks to create a condition that turns ON the alarm only if button1 and button2 are pressed.

PLC Programming

if button1 [1] button2 [2] then
  alarm = ON
end if

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

AAND

BOR

C== TRUE

D!= FALSE

Attempts:

3 left

💡 Hint

Common Mistakes

Using OR will activate alarm if any button is pressed.

Using != FALSE is less clear than == TRUE here.

Using AND and == TRUE ensures both buttons are pressed to activate the alarm.

5fill in blank

hard

Fill all three blanks to create a dictionary that maps sensor names to their status only if the status is ON.

PLC Programming

status_map = { [1]: [2] for [1], [2] in sensors.items() if [2] == [3] }

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

Asensor

Bstatus

C'ON'

D'OFF'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'OFF' in the filter will exclude ON sensors.

Using wrong variable names breaks the comprehension.

The dictionary comprehension uses sensor and status variables and filters for status == 'ON'.

Practice

1. What does series logic with an AND condition mean in PLC programming?

easy

A. The output is true when no input conditions are true

B. Only one input condition needs to be true for the output to be true

C. The output toggles randomly regardless of inputs

D. All input conditions must be true for the output to be true

Solution

1. Step 1: Understand AND condition meaning

   AND means all inputs must be true together to get true output.

2. Step 2: Apply to series logic

   In series logic, inputs are connected so output is true only if every input is true.

3. Final Answer:

   All input conditions must be true for the output to be true -> Option D

4. Quick Check:

   AND means all true = output true [OK]

Hint: AND means every input must be true for output true [OK]

Common Mistakes:

• Thinking only one input needs to be true
• Confusing AND with OR logic
• Assuming output toggles without input conditions

2. Which of the following is the correct syntax for a series AND condition in a PLC ladder logic rung?

easy

A. --( )--[ ]--[ ]-- output before inputs

B. --[ ]--+--[ ]--( )-- where contacts are in parallel

C. --[ ]--[ ]--( )-- where both contacts are in series

D. --[ ]--[ ]--[ ]-- without output coil

Solution

1. Step 1: Identify series AND syntax

   Series AND means contacts connected one after another in a line before output coil.

2. Step 2: Match with options

   --[ ]--[ ]--( )-- where both contacts are in series shows two contacts in series before output coil, which is correct.

3. Final Answer:

   --[ ]--[ ]--( )-- where both contacts are in series -> Option C

4. Quick Check:

   Series contacts before coil = AND logic [OK]

Hint: Series contacts before coil mean AND logic [OK]

Common Mistakes:

• Choosing parallel contacts which mean OR logic
• Placing output coil before inputs
• Missing output coil in the rung

3. Given the following PLC ladder logic snippet with two inputs I1 and I2 in series controlling output Q1:
--[ I1 ]--[ I2 ]--( Q1 )--
What will be the state of Q1 if I1 = TRUE and I2 = FALSE?

medium

A. Q1 will be FALSE

B. Q1 will be TRUE

C. Q1 will toggle ON and OFF

D. Q1 will remain in previous state

Solution

1. Step 1: Analyze input states in series

   Since I1 is TRUE but I2 is FALSE, the series AND condition fails because both must be TRUE.

2. Step 2: Determine output Q1 state

   Output Q1 will be FALSE because the AND condition requires all inputs TRUE.

3. Final Answer:

   Q1 will be FALSE -> Option A

4. Quick Check:

   AND needs all TRUE, here I2 is FALSE, so output FALSE [OK]

Hint: If any input FALSE in series, output is FALSE [OK]

Common Mistakes:

• Assuming output is TRUE if one input is TRUE
• Thinking output toggles without input change
• Ignoring the FALSE input in series

4. Identify the error in this PLC ladder logic snippet intended to implement series AND logic:
--[ I1 ]--+--[ I2 ]--( Q1 )--
|
( )
What is wrong with this design?

medium

A. Inputs I1 and I2 are in parallel, not series

B. Output coil Q1 is missing

C. Input I1 is not connected to power rail

D. There is no error; logic is correct

Solution

1. Step 1: Examine input connection style

   The '+' symbol and branching show I1 and I2 are connected in parallel, not series.

2. Step 2: Understand effect on logic

   Parallel inputs mean OR logic, not AND series logic as intended.

3. Final Answer:

   Inputs I1 and I2 are in parallel, not series -> Option A

4. Quick Check:

   Parallel = OR, not series AND [OK]

Hint: Parallel branches mean OR, series means one after another [OK]

Common Mistakes:

• Confusing parallel with series wiring
• Ignoring ladder diagram symbols
• Assuming output coil is missing

5. You want a motor to start only when three safety switches S1, S2, and S3 are all ON. Which ladder logic snippet correctly implements this series AND condition for output M1?

hard

A. --[ S1 ]--+--[ S2 ]--+--[ S3 ]--( M1 )--

B. --[ S1 ]--[ S2 ]--[ S3 ]--( M1 )--

C. --[ S1 ]--[ S2 ]--+--[ S3 ]--( M1 )--

D. --[ S1 ]--( M1 )--[ S2 ]--[ S3 ]--

Solution

1. Step 1: Identify series AND condition

   All switches must be connected in series (one after another) before output coil.

2. Step 2: Check each option

   --[ S1 ]--[ S2 ]--[ S3 ]--( M1 )-- shows S1, S2, S3 in series before M1 coil, correct for AND logic.

3. Final Answer:

   --[ S1 ]--[ S2 ]--[ S3 ]--( M1 )-- -> Option B

4. Quick Check:

   Series contacts = AND condition for motor start [OK]

Hint: Connect all switches in series before output coil for AND [OK]

Common Mistakes:

• Using parallel branches which create OR logic
• Placing output coil before inputs
• Mixing series and parallel incorrectly