Data Acquisition

Data Acquisition and
Interfacing
Lecture 09

Introduction
A data acquisition system consists of many components that are integrated to:
• Sense physical variables (use of transducers)
• Condition the electrical signal to make it readable by an A/D board
• Convert the signal into a digital format acceptable by a computer
• Process, analyze, store, and display the acquired data with the help of software

Data Acquisition System
Block Diagram

Flow of information in DAQ
1.
2.
3.
4.
5.
6.
7.

Input transducer – measure physical quantity
Output from transducer – conditioned i.e. amplify, filter, conversion Conditioned analog signal – digitized using ADC
Digital information – acquired, process and record by computer Modify physical signal, digital output converted to analog by DAC
Analog signals are conditioned
Output transducer interact with physical variables

Transducers
Sense physical phenomena and translate it into electric signals.
Examples:
•
•
•
•

Temperature
Pressure
Light
Force

•
•
•
•

Displacement
Level
Electric signals
ON/OFF switch

Signal Conditioning
Electrical signals are conditioned so they can be used by an analog input board. Types of signal conditioner:
– Amplification
– Isolation
– Filtering
– Linearization

Analog to Digital (A/D) Converter
• Input signal
• Sampling rate
• Throughput

• Resolution
• Range
• Gain

A/D Converter: Input Signal
• Analog
– Signal is continuous
– Example: strain gage. Most transducers produce analog signals

• Digital
– Signal is either ON or OFF
– Example: light switch.

A/D Converter: Sampling Rate
• Determines how often conversions take place. • The higher the sampling rate, the better.
Analog
Input
4 Samples/cycle

16 Samples/cycle

8 Samples/cycle

A/D Converter: Sampling Rate
• Aliasing
– Acquired signal gets distorted if sampling rate is too small.

A/D Converter: Resolution

Bits
The smallest