Data Acquisition and Filtering Assignment Help
A computer is not able to directly process the raw analog signals but it requires an interfacing device that modifies the raw signal accordingly. Data Acquisition and Filtering are the interfacing stages between a computer and the real world. It comprises three major stages. Signal processing initiates with sensing the real-time signal, it is done by a transducer which converts a physical quantity to an analog signal. For example, if we need to analyze a heat signal, we will first use a thermocouple which transforms the temperature into electrical form (analog signal). Analog signals are sensed by transducers but there is inherent noise associated with them. Moreover, power line interference may also produce harmonics in the processed signal. The system senses data from different kinds of sensors at a time, therefore, it is imperative to modify them into a uniform nature. Sometimes, it may be hazardous for the system to directly input the signal, therefore, an isolator is needed in a few cases. For instance, biomedical devices are directly connected to a human body, therefore, a buffer is necessary for biomedical devices to ensure that the devices do not draw a large current. Before further processing the signal, it is necessary to mitigate or condition the noise at the initial stage. Hence, a band-pass filter is employed at the input stage for reducing power-line interference. It is computationally complex and cumbersome to process analog signals in their actual forms. Secondly, the filtered data is then digitized at a specified resolution because a processing unit accepts data in digital form only. This analog to digital conversion may introduce noise in the signal. The modified data is then transmitted to a computer through a data bus. CPU processes the data, extracts useful information and displays meaningful data on the user interface. After this, reversal starts in which the digital signal is converted back to the analog form which can easily be used to interpret or analyze the data nature.
Analog signals are typically in microvolts or millivolts and have a low frequency, to efficiently process the signal, operational amplifiers and filters with low cut-off level are included at the acquisition stage to amplify and filter the measured signal to the desired level. Filters are used between different stages of processing devices to filter the noise generated by the instrument.
One example of the Data Acquisition system is the ECG plotter. The circuit measures and modifies heartbeats and plots them on an oscilloscope. Its transducers are three leads connected to the human body. Heartbeats are ionic signals, leads convert them into electrical signals. Heartbeats have a magnitude of a very low order, consequently, ECG employs three op-amps to amplify the signal to a suitable level. The operational amplifier also offers high input impedance which prevents the current surge. ECG signal is prone to both external and internal noises. Internal noises are generated by circuitry while external by transducers.