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Signal conditioning and data acquisition system in engineering

By Edited Nov 13, 2013 0 0

Concept of signal conditioning in field of engineering

Signal conditioning is basically the process of making modification in the original signal. This modification may be carrying different types of purposes along with it like making the signal usable at the oncoming stages of the particular system, changing it from one form to another one so that required processing may be done over it. Here are some quantities which are used n conditioning of the system which will be discussed about it our farther talk. Measurand, which is the basically a physical quantity as is detected by the first stage of the instrumentation or measurement system. The first stage with which we have become familiar is actually called detector transducer stage.

The quantity is detected and then transduced into to another form like electrical form and this is the most common case. The output of the stage followed has to be modified before it becomes usable and satisfactory to drive the signal presentation stage which is the third and the last of a a measurement system. The last stage of the measurement system may consist of indicating, recording displaying; data processing elements o ether can also be some control elements. Here methods used for modifying the transduced signal into a usable format for the final stage of the measurement system are described. The measurement of dynamic physical quantities requires faithful representation of their analogue or digital output obtained from the intermediate stages this can be signal conditioning stage and this places a severe stain on the signal conditioning equipment. The signal condition equipment may be required to do linear processing like amplification of the weak signal and their attenuation called attenuation integration, addition and subtraction. They are also required to do non-linear processing like modulation of the signal obtained, its demodulation sampling of the signal, filtering and clipping and also clamping squaring the signal, liberalizing or multiplication by another function and many more like them. These tasks are by no means simple but very complicated by the virtue of accomplishment and coordination with other sections of the system.

Signal conditioning and Data acquisition and block diagram

Signal condition or also called data acquisition equipment in many a situation is an excitation and amplification system for passive transducers. It may be an amplifier system for active transducer. In both the applications the transducer output is brought up to a sufficient level to make it useful for conversion, process indication and also for recording the result for future use. Excitation used for passive transducers because of the reason that these transducers do not make the voltage and current of their own. So this is the reason that the transducers like stain gauss, potentiometer, resistance thermometer, inductive transducer, capacitive transducer requires excitation from some external mean.

There are also many active transducers like technogenerators, thermocouple, inductive pick up and piezo-electric crystals, on the other hand, do not requires an external source of excitation since they produce their own electrical output on the account of application of the physical quantities. But these signals usually have low voltage level and hence need amplification to make it possible to feed to oncoming stages of the system so that required result may be obtained. The excitation sources may be an alternative or direct (D.C.) voltage source. The D.C. system is comparatively simpler and this can also shown with the help of the following figure which is actually a block diagram of the functioning which actually occurs.


Block diagram of signal condition system

The resistance transducer like strain gauges, constitute one arm or more than one arm of a wheat stone bridge which is excited by an isolated D.C. source. The bridge can be balanced by a potentiometer and can also be calibrated for unbalanced conditions.

Some points about the transducers used in signal conditioning

The transducers used are the variable resistance or variable inductor type of transducer. They are employed in between carrier frequencies of 50 Hz to 200 kHz, the carrier frequency is much higher, and they are at least 5 to 10 times the signal frequencies. Transducer parameter variation amplitude modulate the carrier frequencies at the bridge output and wave form is amplitude and demodulated. The demodulation is phase sensitive so that the polarity of D.C. output indicates the direction of the parameter changes in the bridge output. In carrier system amplitude drift and spurious signal are not much important unless they modulate the carrier. However, it is more difficult to achieve a stable carrier oscillator than a comparable D.C. stabilized source. In carrier systems, it is easier to obtain very high rejection of frequency pick up. Active filters can be used to reject this frequency and prevent overloading of A.C. amplifier. The phase sensitive, demodulators filters out carrier frequency components of the data signal.


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