Data Acquisition

Data acquisition is a computer technique used to convert the measure of an electric or physical phenomenon like current, voltage, temperature, pressure or sound. The computer-based acquisition uses a structural hardware, software and a computer to find out the measurements. The mechanism of data acquisition is separate for each individual component. However, it shares a common characteristic of acquiring, analyzing and presenting information.

Data acquisition software incorporate different features like:

• Sensors: They help in converting physical parameters into electrical signals.
• Signal conditioning circuitry: This helps in converting sensor signals into digital values.
• Analog-Digital Converters: This helps in converting analog signals into digital signals.

A DAQ controller usually controls data acquisition applications. However, if there are any custom made applications, then the DAQ software is developed by using various general-purpose programming languages like BASIC or C. There are many specialized programming languages for developing data acquisition and they include EPICS, LabVIEW and MATLAB.

How is data acquisition performed?

Data acquisition begins with the measurement of physical properties or physical phenomenon like temperature, pressure, light intensity, fluid flow, and force. The measurement is not performed on the direct physical property. It is converted into a unified form and then this sample data is being analyzed and measured by the data acquisition system. The devices called sensors conduct these tasks of the data acquisition system or data acquisition software.

Transducer, which is a type of sensor, converts the physical properties into an electrical signal or into the corresponding electrical character like resistance or capacity, which in turn can be converted into an electrical signal. The ability of the data acquisition system depends on the performance of these sensors their effectiveness in transforming the physical properties into electrical signals. The sensors of these systems are specific according to the applications used. Sometimes, DAQ also employs different techniques in one system. For example, there can be a system to convert the physical properties into electrical signals and then electrical signals are converted into digital signals.

Signal conditioning is used in the data acquisition equipment if transducer is not capable of producing the signal that can be used in the DAQ hardware controller. Many types of signal conditioning are used in the data acquisition systems depending on the transducer used. The signal from the transducer can be modified using the signal conditioning based on the requirement. Examples of signal conditioning include, signal amplification, filtering of the signal, lock-in amplifier to perform demodulation, isolation, bridge completion, linearization and so on.

DAQ Hardware and Software:

DAQ hardware is an interface in between the computer and the signals. It can be in the form of a device that can be connected to the serial or parallel ports or to a USB. DAQ hardware is also available in the form of cards that can be connected to the PCI, ISA, PCI-E slots on the motherboard. However, the usual preference is the external device as it gives ample space at the back for different connections and is easy to access.

DAQ software is usually the packaged application that supports the DAQ hardware interfaces. It comes in three different forms, low-level software that supports the device drivers of the hardware devices, off-the shelf applications that helps in programming like log, analyze and display of the acquired data, and the applications that can directly registered with the hardware components.

Article published December 4th, 2009
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