Block Description: Basic elements required for Data acquisition System are (1) Transducer. (2) Amplifiers or signal conditioners. (3) Multiplexers. (4) Sample and Hold circuit . (5) Analog to Digital converters.
(1)Transducer It is desirable that an emf obtained from transducer is proportional to quantity being measured, is used as input to the data acquisition system thus transducers such as thermocouple, strain gauges and piezoelectric devices etc. are used. An exception to this usual function of transducer ,some sensor produces frequency which can be counted with electronic counter to obtain integral of measured quantity.
(2) Amplifiers or signal conditioning EquipmentSignal conditioning Equipment includes any equipment that assists in transforming the output of transducer to the desired magnitude or form required by next stage of the DAS. It produces the required conditions in the transducers so that they work properly. Signal conditioners may include devices for amplifying, refining, or selecting certain positions of these signals. Examples of signal conditioning equipment include known constant voltage sources for strain gauge bridges, zero bridge balance devices for strain gauge circuits, temperature control devices for thermocouple junctions, voltage amplifiers and servo-systems.
(3)Multiplexers. Multiplexing is the process of sharing a single channel with more than one output. The multiplexer accepts multiple analog inputs and connects them sequentially to one measuring input. Multiplexing is a means of using the same transmission channel for transmitting more than one quantity. Multiplexing becomes necessary in measurement systems when the distance between transmitting and receiving point is large and many quantities are to be transmitted. If a separate channel is used for each quantity, the cost of installation, maintenance, and periodic replacement becomes prohibitively large and therefore a single channel is used which is shared by the various quantities. Multiplexing is commonly accomplished by either time or frequency sharing of the transmission channel between the individual quantities.
(4)A/D Converters A/D converter based on dual slope techniques are useful of low frequency data, such as from thermocouples or analog devices.