Describe data retrieval and plotting. How can plots help in interpreting measurement data?

Question

Accepted Answer

## Data Retrieval and Plotting

### Data retrieval
Retrieval means reading the stored data back for analysis.

```mermaid
flowchart LR
  A[Storage: SD card or logger memory] --> B[Transfer via USB UART Ethernet]
  B --> C[Import into PC software]
  C --> D[Parse and clean data]
  D --> E[Plot and analyse]
```

- Data is saved as CSV, TXT or binary files, often with timestamps.
- Tools: Excel, MATLAB, Python (pandas, matplotlib), LabVIEW, vendor software.
- Cleaning: remove invalid samples, fill gaps, convert units.

### Plotting
| Plot | Use |
|---|---|
| Line plot (value vs time) | Trends, drift, signal waveform |
| Scatter plot | Relationship between two variables, calibration |
| Histogram | Distribution of measurements |
| Spectrum plot (FFT) | Frequency content, noise peaks |
| Bar chart | Comparison of channels or groups |
| Box plot | Spread and outliers |

### How plots help interpretation
1. Show trends, peaks, steps and drift quickly.
2. Reveal outliers and sensor faults.
3. Show noise and interference (e.g. 50 Hz in the spectrum).
4. Allow comparison of channels, trials or conditions.
5. Verify calibration through a fitted line and its slope.
6. Communicate results clearly to others.

Good plots have labelled axes with units, a title, a legend and a suitable scale.

### Exam tip
Mention retrieval steps first, then 3 plot types and 4 benefits.

Data Retrieval and Plotting

Data retrieval

Plotting

How plots help interpretation

Exam tip

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