Answer

Correct option: (ii) Converting physical quantities into digital data

Explanation

A Data Acquisition (DAQ) system collects real-world physical signals and converts them into a form that a computer or microcontroller can process.

A typical DAQ sequence is:

Physical quantity → Sensor → Signal Conditioning → ADC → Digital Data → Processing/Storage

For example, a temperature sensor produces an electrical signal corresponding to temperature. The signal is conditioned if required and then converted into a digital value by an Analog-to-Digital Converter (ADC).

Why the other options are incorrect

• (i) Data storage: Storage may be included in a DAQ system, but it is not its primary purpose.
• (iii) Wireless communication: Wireless communication may be used for transmitting acquired data, but it is not the fundamental purpose of DAQ.
• (iv) Power amplification: Power amplification is not the primary function of a DAQ system.

Therefore, the correct answer is (ii).

Solution: Architecture and Working of a Data Acquisition System (DAQ)

Definition

A Data Acquisition System (DAQ) is a system used to collect physical measurements from the real world, convert them into electrical and digital signals, process the acquired data, and finally display, store, or transmit the information.

Examples include temperature measurement, vibration monitoring, motor-speed measurement and heart-rate monitoring.

Basic Block Diagram

Physical Quantity
       ↓
Sensor / Transducer
       ↓
Signal Conditioning
       ↓
Multiplexer (for multiple channels)
       ↓
Sample & Hold
       ↓
ADC
       ↓
Microcontroller / Computer
       ↓
Processing → Storage → Display / Communication / Control

Main Components

1. Sensor / Transducer

Converts a physical quantity such as temperature, pressure, displacement or heart rate into an electrical signal.

2. Signal Conditioning

Prepares the sensor output for digitization. It may involve:

• Amplification
• Filtering
• Isolation
• Linearization
• Level shifting

3. Multiplexer

In a multichannel DAQ, a multiplexer selects one input channel at a time and sends it to the acquisition path.

4. Sample-and-Hold

Samples the analog signal and holds its value constant during ADC conversion when required by the ADC architecture.

5. ADC

The Analog-to-Digital Converter converts the conditioned analog voltage into a digital number. For an ideal $n$-bit ADC with input range $V_{FS}$, the approximate LSB size is:

$$LSB = \frac{V_{FS}}{2^n}$$

6. Microcontroller / Computer

Processes the digital samples, performs calculations and may execute control algorithms.

7. Storage and Display

Data can be stored in memory, SD cards or a computer and presented as numerical values, graphs or reports.

Working

1. The physical parameter is measured by a sensor.
2. The sensor produces an electrical signal.
3. Signal conditioning amplifies, filters and scales the signal.
4. The multiplexer selects a channel when multiple sensors are present.
5. The signal is sampled and converted into digital form by the ADC.
6. The microcontroller or computer processes the digital samples.
7. The resulting information is stored, displayed, transmitted or used for automatic control.

Single-Channel and Multichannel DAQ

Type	Description
Single-channel	Acquires data from one sensor/input.
Multichannel	Acquires data from several sensors/inputs using multiplexing or multiple ADC channels.

Applications

• Temperature data logging
• Motor-speed monitoring
• Industrial process control
• Vibration monitoring
• Heart-rate monitoring
• Environmental monitoring
• Biomedical instrumentation

Conclusion

A DAQ system forms the complete measurement chain from physical quantity → sensor → signal conditioning → ADC → digital processing → storage/display/control. Its accuracy depends on sensor quality, conditioning, sampling rate, ADC resolution and proper noise reduction.