Sample time configuration in Simulink - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Sample Time Types in Simulink

Which of the following sample time types in Simulink represents a fixed discrete rate?

A Inherited sample time

B Continuous sample time

C Discrete sample time

D Variable-step sample time

💡 Hint

Think about which sample time type runs at fixed intervals.

Discrete sample time runs at fixed intervals, unlike continuous or inherited sample times.

❓ Predict Output

intermediate

Sample Time Output of a Discrete Block

What is the sample time output of a Discrete-Time Integrator block configured with a fixed step size of 0.1 seconds?

Simulink

Step size = 0.1 seconds
Block: Discrete-Time Integrator

A Sample time = 0.1

B Sample time = -1

C Sample time = 1

D Sample time = 0

💡 Hint

The sample time matches the fixed step size for discrete blocks.

The Discrete-Time Integrator block outputs at the fixed step size, so sample time is 0.1 seconds.

❓ data_output

advanced

Determining Sample Time from Model Configuration

A Simulink model is configured with a fixed-step solver of 0.05 seconds. A block inside the model has sample time set to -1 (inherited). What is the effective sample time of this block?

A -1 (inherited, no fixed value)

B 0.05 seconds

C 0 seconds (continuous)

D Variable depending on input

💡 Hint

Inherited sample time takes the solver step size if discrete.

With a fixed-step solver of 0.05 seconds, inherited sample time resolves to 0.05 seconds.

🔧 Debug

advanced

Identifying Sample Time Conflict Error

Given two connected blocks in Simulink: Block A has sample time 0.1 seconds, Block B has sample time 0.05 seconds. What error will occur when simulating?

A Sample time propagation conflict error

B Continuous sample time error

C No error, simulation runs normally

D Solver configuration error

💡 Hint

Blocks connected with different discrete sample times cause conflicts.

Simulink requires connected blocks to have compatible sample times; differing discrete times cause conflicts.

🚀 Application

expert

Optimizing Model Performance with Sample Time Configuration

You have a Simulink model with multiple discrete blocks running at different sample times: 0.01s, 0.1s, and 1s. To optimize simulation speed without losing accuracy, which approach is best?

A Set all blocks to the fastest sample time (0.01s) to synchronize updates.

B Set all blocks to inherited sample time and rely on solver to decide.

C Set all blocks to continuous sample time to avoid discrete steps.

D Use rate transition blocks to manage different sample times and keep blocks at their own rates.

💡 Hint

Consider how to handle multiple rates efficiently in Simulink.

Using rate transition blocks allows blocks to run at their own sample times while managing data transfer safely, optimizing speed and accuracy.

Practice

1. What does the sample time in Simulink control?

easy

A. The color of the block in the model

B. How often a block executes during simulation

C. The size of the block on the screen

D. The type of data the block processes

Solution

1. Step 1: Understand sample time meaning

   Sample time defines the frequency at which a block runs during simulation.

2. Step 2: Match sample time to options

   Only How often a block executes during simulation describes execution frequency, others describe unrelated features.

3. Final Answer:

   How often a block executes during simulation -> Option B

4. Quick Check:

   Sample time = execution frequency [OK]

Hint: Sample time means block run frequency [OK]

Common Mistakes:

• Confusing sample time with block appearance
• Thinking sample time controls data type
• Assuming sample time affects block size

2. Which of the following is the correct way to set a fixed sample time of 0.1 seconds in a Simulink block?

easy

A. Set Sample time to 'inf'

B. Set Sample time to '-1'

C. Set Sample time to '0.1'

D. Set Sample time to 'triggered'

Solution

1. Step 1: Identify fixed sample time syntax

   Fixed sample time is set by a positive number representing seconds, e.g., 0.1.

2. Step 2: Evaluate options

   '-1' means inherited, 'inf' means continuous, 'triggered' is not a numeric value.

3. Final Answer:

   Set Sample time to '0.1' -> Option C

4. Quick Check:

   Fixed sample time = positive number [OK]

Hint: Fixed sample time is a positive number [OK]

Common Mistakes:

• Using '-1' for fixed sample time
• Confusing 'inf' with fixed sample time
• Entering non-numeric values for sample time

3. Consider a Simulink model with two blocks: Block A has a sample time of 0.05 seconds, and Block B has a sample time of 0.1 seconds. If the simulation runs for 0.2 seconds, how many times will Block A execute?

medium

A. 4 times

B. 3 times

C. 5 times

D. 2 times

Solution

1. Step 1: Calculate executions for Block A

   Block A runs every 0.05 seconds. Total simulation time is 0.2 seconds. Executions occur at t=0, 0.05, 0.1, 0.15 (not at 0.20 since simulation ends at 0.2).

2. Step 2: Divide total time by sample time

   Number of executions = (0.2 / 0.05) = 4 (executions at 0, 0.05, 0.1, 0.15).

3. Final Answer:

   4 times -> Option A

4. Quick Check:

   Executions at t=0, 0.05, 0.1, 0.15 = 4 times [OK]

Hint: Number of executions = floor(total time / sample time) + 1 [OK]

Common Mistakes:

• Forgetting the initial execution at t=0
• Confusing Block A's sample time with Block B's
• Counting execution at simulation end time incorrectly

4. You set a block's sample time to '-1' but the block does not inherit the sample time as expected. What is the most likely cause?

medium

A. The block has a fixed sample time set elsewhere

B. The sample time value '-1' is invalid

C. The block is set to continuous sample time

D. The block is inside a triggered subsystem

Solution

1. Step 1: Understand '-1' sample time meaning

   Sample time '-1' means inherit from parent or driving block.

2. Step 2: Identify why inheritance fails

   If block is inside a triggered subsystem, inheritance may not work because triggered subsystems have their own timing.

3. Final Answer:

   The block is inside a triggered subsystem -> Option D

4. Quick Check:

   Triggered subsystem blocks may block inheritance [OK]

Hint: Triggered subsystems block sample time inheritance [OK]

Common Mistakes:

• Thinking '-1' is invalid
• Ignoring subsystem context
• Assuming continuous sample time causes issue

5. You want to speed up your simulation by reducing the number of block executions but keep accuracy high. Which sample time configuration strategy is best?

hard

A. Use a larger fixed sample time for less critical blocks and smaller for critical ones

B. Set all blocks to continuous sample time

C. Set all blocks to inherited sample time '-1'

D. Use triggered sample time for all blocks

Solution

1. Step 1: Understand trade-off between speed and accuracy

   Larger sample times reduce executions but may reduce accuracy; smaller sample times increase accuracy but slow simulation.

2. Step 2: Apply selective sample time setting

   Assign larger sample times to less critical blocks and smaller to critical blocks to balance speed and accuracy.

3. Final Answer:

   Use a larger fixed sample time for less critical blocks and smaller for critical ones -> Option A

4. Quick Check:

   Selective sample time balances speed and accuracy [OK]

Hint: Adjust sample times by block importance [OK]

Common Mistakes:

• Setting all blocks to continuous slows simulation
• Using inherited sample time everywhere loses control
• Triggering all blocks may cause unnecessary executions