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Significance of SoCs in DAQ development

Posted: 07 Nov 2013     Print Version  Bookmark and Share

Keywords:Data acquisition systems  DAQ  signal conditioning  sensors  ADC 

Data acquisition systems (DAQ) measure real world signals (temperature, pressure, humidity etc.). DAQs do it through performing appropriate signal conditioning on a raw signal (amplification, level shifting, etc.), and then digitizing and storing these signals. This digital signals can then be transmit to another digital system for further processing, usually on a periodic basis.

Examples of data acquisition systems include such applications as weather monitoring, recording a seismograph, pressure, temperature and wind strength and direction. This information is fed to computers, which then predict natural events like rain and calamities like earthquakes and destructive winds. An example of a DAQ in the medical field is a patient monitoring system that tracks signals like an Electro-cardiogram (ECG) or Electro-encephalogram (EEG).

A typical DAQ consists of the following components:

 • Sensors that convert real world phenomenon to equivalent electrical analogue signals
 • Signal conditioning circuitry that alters signals from the sensor to a form, which can be digitized
 • Analogue to digital converters (ADC) that convert conditioned analogue signals to a digital representation
 • Store and forward memory, which is used to store digital signal streams for forwarding to another system at a later time
 • A communication interface over which the digital streams are transferred to the other system
 • A microprocessor system or a microcontroller to sequence and control all of the other components.

Figure: Data acquisition system to acquire data from a single sensor.

The figure shows a block diagram of a basic data acquisition system. The details of these internal blocks are explained in the next section.

Sub-systems of a data acquisition system
Sensors: As discussed in the previous section, Data Acquisition Systems track physical parameters such as temperature, pressure, humidity, flow rate, etc. Since processing is flexible to be done in the electrical domain, these parameters are converted into an electrically measurable quantity such as change in resistance or current or voltage by using appropriate sensors. For instance, transducers like thermistors, RTDs (Resistance Temperature detectors) etc. change their resistance with respect to temperature and pressure transducers like strain gauge provide change in resistance with respect to the applied pressure. These can be converted to an electrical quantity like voltage using a wheatstone's bridge [1].

Table 1 lists some of the common physical parameters, which are being monitored in DAQs and also the appropriate sensors/ transducers used.

Table 1: Commonly use electrical transducers.

Isolation
Applications that involve signal acquisition can damage the system in cases where very high voltage signals are being processed. Stepping down these high voltages using a transformer or providing other protection circuitry like optical isolation are highly recommended [2].

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