Component of Data Acquistion System

Data Acquisition System And Interfacing to the computer:

Data Acquisition System(DAS) is the instrumentation system where specific data is acquired reliably, economically and efficiently. Data acquisition is the process of sampling signals that measure real world physical conditions and converting the resulting samples into digital numeric values that can be manipulated by a computer. Data acquisition systems, abbreviated by the acronymsDASorDAQ, typically convert analog waveforms into digital values for processing. A simplified block diagram of a typical data acquisition system is shown below:

Main components of a typical data acquisition system are:
• Transducers and sensors
• Signals
• Signal conditioning
• DAQ hardware
• Driver and application software

1.Transducers and sensors:

Transducers are devices that transform physical parameters (such as temperature, pressure, flow, and strain) into electrical parameters (such as voltage, current, and resistance). The electrical parameter is measured by measurement hardware and the result is converted to engineering units. For example, when measuring a thermocouple, the measurement hardware actually reads a dc voltage, which it then converts to a corresponding temperature using a mathematical algorithm. The following table shows several types of transducers with their corresponding output

2.Signals:

The appropriate transducers convert physical phenomena into measurable signals. However, different signals need to be measured in different ways. For this reason, it is important to understand the different types of signals and their corresponding attributes. Signals can be categorized into two groups:

i.) Analog Signals

ii.)Digital Signals

Analog Signals

An analog signal can exist at any value with respect to time. A few examples of analog signals include voltage, temperature, pressure, sound, and load. The three primary characteristics of an analog signal are level, shape, and frequency

Digital Signals

A digital signal cannot take on any value with respect to time. Instead, a digital signal has two possible levels: high and low. Digital signals generally conform to certain specifications that define the characteristics of the signal. They are commonly referred to as transistor-to-transistor logic (TTL). TTL specifications indicate a digital signal to be low when the level falls within 0 to 0.8 V, and the signal is high between 2 and 5 V. The useful information that you can measure from a digital signal includes the state and the rate.

3.Signal conditioning:

Signal conditioning is used to amplify, attenuate, shape, or isolate signals from transducers before they are sent to the measurement hardware. Signal conditioning converts the signal to a form that is better measured by the system, or in some cases, makes it possible to measure the signal at all. Examples of signal conditioning include:

• Amplification of small signals
• Attenuation of large signals
• Thermocouple compensation for temperature measurements
• Current sourcing for 2-wire and 4-wire resistance measurements
• Filtering to remove system noise
• Shunt resistors for current measurements

In some data acquisition systems, the signal conditioning components are incorporated internally within the system. These systems can measure dc voltage, ac voltage, resistance, frequency, current, and temperature on any input channel without the need for external signal-conditioning components.

4.Data acquisition hardware:

Data acquisition hardware acts as the interface between the computer and the outside world. It primarily functions as a device that digitizes incoming analog signals so that the computer can interpret them. Other data acquisition functionality includes the following:

a.Analog input/output
b.Digital input/output
c.Counter/timers
d.Multifunction(combination of analog, digital, and counter operations on a single device)

5.Driver and application software:

Data acquisition applications are usually controlled by software programs developed using various general purpose programming languages such asAssembly,BASIC,C,C++,C#,Fortran,Java,LabVIEW,Pascal etc. Stand-alone data acquisition systems are often called data loggers.

Driver Software

Software transforms the PC and the data acquisition hardware into a complete data acquisition, analysis, and presentation tool. Without software to control or drive the hardware, the data acquisition device does not work properly. Driver software is the layer of software for easily communicating with the hardware. It forms the middle layer between the application software and the hardware. Driver software also prevents a programmer from having to do register-level programming or complicated commands to access the hardware functions.

Application Software

The application layer can be either a development environment in which you build a custom application that meets specific criteria, or it can be a configuration-based program with preset functionality. Application software adds analysis and presentation capabilities to driver software. To choose the right application software, we should evaluate the complexity of the application, the availability of configuration-based software that fits the application, and the amount of time available to develop the application. If the application is complex or there is no existing program, use a development environment.

References-

1.www.newark.com/dataacquistionsystem

2.https://en.wikipedia.org/wiki/Data_acquisition