Sample time configuration in Simulink - Step-by-Step Execution

Concept Flow - Sample time configuration

Start Simulation

↓

Check Sample Time

↓

Continuous

↓

Integrate

↓

Output Signal

↓

End Simulation

Simulation starts, checks if block uses continuous or discrete sample time, then processes accordingly before output.

Execution Sample

Simulink

sampleTime = 0.1
t = 0.0
while t <= 1.0:
    output = f"Output at {t}"
    print(f"Time {t}: Output {output}")
    t += sampleTime

Simulates discrete sample time steps of 0.1 seconds, outputs signal value at each step.

Execution Table

Step	Time (t)	Sample Time Check	Action	Output
1	0.0	t % 0.1 == 0	Calculate output	Output at 0.0
2	0.1	t % 0.1 == 0	Calculate output	Output at 0.1
3	0.2	t % 0.1 == 0	Calculate output	Output at 0.2
4	0.3	t % 0.1 == 0	Calculate output	Output at 0.3
5	0.4	t % 0.1 == 0	Calculate output	Output at 0.4
6	0.5	t % 0.1 == 0	Calculate output	Output at 0.5
7	0.6	t % 0.1 == 0	Calculate output	Output at 0.6
8	0.7	t % 0.1 == 0	Calculate output	Output at 0.7
9	0.8	t % 0.1 == 0	Calculate output	Output at 0.8
10	0.9	t % 0.1 == 0	Calculate output	Output at 0.9
11	1.0	t % 0.1 == 0	Calculate output	Output at 1.0
12	1.1	t > 1.0	Stop simulation	No output

💡 Time exceeds simulation stop time, simulation ends.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	After 6	After 7	After 8	After 9	After 10	Final
t	0.0	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9	1.0	1.1
output	Output at 0.0	Output at 0.1	Output at 0.2	Output at 0.3	Output at 0.4	Output at 0.5	Output at 0.6	Output at 0.7	Output at 0.8	Output at 0.9	Output at 1.0	N/A

Key Moments - 2 Insights

Why does the output only update at multiples of the sample time?

Because the simulation checks if the current time is a multiple of the sample time (see execution_table rows 1-11), output updates only at these discrete times.

What happens if the time is not a multiple of the sample time?

The simulation does not calculate output and stops or waits (see execution_table row 12), because discrete sample time blocks only update at defined intervals.

Visual Quiz - 3 Questions

Look at the execution table, what is the output at step 5?

A Output at 0.4

B Output at 0.5

C No output

D Output at 0.3

💡 Hint

Check the 'Output' column at step 5 in the execution_table.

At which step does the simulation stop due to time exceeding the limit?

A Step 10

B Step 12

C Step 11

D Step 9

💡 Hint

Look at the 'Action' column for the stop simulation note in execution_table.

If sample time changed to 0.2, how would the output update steps change?

A Output updates every 0.05 seconds

B Output updates every 0.1 seconds

C Output updates every 0.2 seconds

D Output updates continuously

💡 Hint

Sample time controls how often output updates, see concept_flow and execution_table.

Concept Snapshot

Sample time controls when blocks update in Simulink.
Continuous sample time updates constantly.
Discrete sample time updates at fixed intervals.
Set sample time to control simulation steps.
Output updates only at multiples of sample time.

Full Transcript

This visual execution shows how sample time configuration works in Simulink. The simulation starts and checks the sample time. If the block uses discrete sample time, it updates output only at multiples of that sample time, for example every 0.1 seconds. The execution table traces each time step, showing output calculation at each multiple of 0.1 seconds. When time exceeds the simulation stop time, the simulation ends. Variables like time and output change step by step. Key moments clarify why output updates only at sample times and what happens otherwise. The quiz tests understanding of output timing and simulation stopping. The snapshot summarizes sample time behavior simply.

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