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.