Describe the block diagram and working of a basic data acquisition system. Explain single-channel and multichannel DAQ systems.

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Accepted Answer

## Data Acquisition System (DAS)

A DAQ system collects physical signals (temperature, pressure, strain, biopotential), converts them to digital form and sends them to a computer or microcontroller for display, storage and analysis.

### Block diagram
```mermaid
flowchart LR
  A[Physical quantity] --> B[Sensor or transducer]
  B --> C[Signal conditioning]
  C --> D[Sample and hold]
  D --> E[ADC]
  E --> F[Processor or computer]
  F --> G[Display and storage]
```

### Working
| Block | Function |
|---|---|
| Sensor / transducer | Converts the physical quantity into an electrical signal |
| Signal conditioning | Amplifies, filters, isolates and linearizes the signal |
| Sample and hold | Freezes the input while the ADC converts |
| ADC | Converts the analog value to a digital code |
| Processor / PC | Processes, scales and logs the data |
| Display / storage | Shows results and saves them |

### Single-channel DAQ
One sensor feeds one conditioning circuit and one ADC. It is simple and cheap, and used when only one quantity is measured.

### Multichannel DAQ
Many sensors are measured with one ADC by a **multiplexer (MUX)** that selects one channel at a time, or by one ADC per channel.

```mermaid
flowchart LR
  S1[Sensor 1] --> M[Analog multiplexer]
  S2[Sensor 2] --> M
  S3[Sensor 3] --> M
  M --> SH[Sample and hold]
  SH --> AD[ADC]
  AD --> P[Processor]
  P -->|select lines| M
```

| Point | Single-channel | Multichannel |
|---|---|---|
| Sensors | One | Many |
| Components | Few | MUX, extra control |
| Cost | Low | Higher but shares ADC |
| Sampling | Continuous | Sequential, per-channel rate is lower |

### Exam tip
Draw both block diagrams and mention that the multiplexer shares one ADC to save cost.

Data Acquisition System (DAS)

Block diagram

Working

Single-channel DAQ

Multichannel DAQ

Exam tip

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