Sample time configuration in Simulink - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set a fixed-step sample time of 0.1 seconds.

Simulink

set_param('model','Solver','FixedStepDiscrete','FixedStep',[1])

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

A'0'

B'auto'

C'0.1'

D'inf'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'auto' instead of a numeric string for FixedStep.

Leaving FixedStep as '0' which disables fixed-step.

Using 'inf' which is invalid for fixed-step size.

The fixed-step sample time is set by specifying the 'FixedStep' parameter as '0.1' seconds.

2fill in blank

medium

Complete the code to configure a block with a sample time of 0.05 seconds.

Simulink

set_param('model/Block','SampleTime',[1])

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

A'-1'

B'-2'

C'inf'

D'0.05'

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-1' which means inherited sample time.

Using 'inf' which means continuous sample time.

Using '-2' which is invalid.

The SampleTime parameter is set to '0.05' seconds as a string to specify the block sample time.

3fill in blank

hard

Fix the error in setting the sample time to discrete with period 0.2 seconds.

Simulink

set_param('model','Solver','FixedStepDiscrete','FixedStep',[1])

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

A0.2

B'0.2'

C'auto'

D'0'

Attempts:

3 left

💡 Hint

Common Mistakes

Passing 0.2 as a number instead of a string.

Using 'auto' which disables fixed-step.

Using '0' which disables fixed-step.

The FixedStep parameter must be a string representing the step size, so '0.2' is correct.

4fill in blank

hard

Fill both blanks to set a block's sample time to inherited and enable sample time override.

Simulink

set_param('model/Block','SampleTime',[1],'AllowSampleTimeOverride',[2])

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

A'-1'

B'on'

C'off'

D'0.1'

Attempts:

3 left

💡 Hint

Common Mistakes

Using '0.1' instead of '-1' for inherited sample time.

Setting AllowSampleTimeOverride to 'off' which disables override.

SampleTime '-1' means inherited sample time, and AllowSampleTimeOverride 'on' enables overriding.

5fill in blank

hard

Fill all three blanks to configure a model with variable-step solver, continuous sample time, and zero fixed step.

Simulink

set_param('model','Solver',[1],'FixedStep',[2],'SampleTime',[3])

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

A'VariableStepDiscrete'

B'0'

C'inf'

D'FixedStepDiscrete'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'FixedStepDiscrete' instead of 'VariableStepDiscrete' for solver.

Setting FixedStep to a non-zero value for variable-step solver.

Using SampleTime other than 'inf' for continuous time.

VariableStepDiscrete solver is used for variable-step, FixedStep '0' disables fixed step, and SampleTime 'inf' means continuous.

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