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S A NC FC SHD ADC ? DS М P S A NC FC SHD АDC а S A NC FC SHD CDev АS S A NC b FC SHD МP АDC Sensor (S)–converts arbitary physical quantity into electric signal Adaptor (A)–provides signal amplification to a required level; expands a dynamic range of input signal; sensor adjustment and other DCP channel elements according to the load. Normalization circuit (NC)– is used as a filter, unwanted low-frequency and high frequency components are removed from the signal Functional conversion (FC) of analog signal is carried out in order to implement units in sensor structure to display definite mathematical operations and improve its accuracy parameters. Sample and hold device(SHD) – is used to store analog signal for a transformation time period of ADC Analog-to-digital converter (ADC) –transforms analog signal into a digital code Digital switch (DS) – selects a channel and transmits data to a microprocessor. Microprocessor (MP) – on the one hand, it is a complex program-driven device, on the other hand, it is an enormous integrated circuit. Operational amplifier (OA) – is an analog integrated environment (IE), voltage is formed on its output, this voltage is equal to a gain difference between two input voltages . U2 _ U0 U1 + Рис. 1.2 U O K OL U1 U 2 OA is totally insensitive to any components of input signals common to both OA inputs. It is called a commonmode signal and is given by U1 U 2 U i com mod 2 Ideal frequency selective filter– a device or system which has a gaintransfer characteristic between input and output; it is constant in a certain frequency bandwidth and there is a naught output in a stopband. Advantages of an active filter compared with a passive filter : Gain. The active filter with a maximum gain-transfer characteristic can be greater than unity. Minimal load impact. A gain-transfer characteristic of an active filter is practically independent of the load the filter works for and a source that controls the filter. Non-inductive filters. To design an active filter only resistors and capacitors are required, inductance is not required. This feature is particularly important when operating at relatively low frequencies (<10 Hz), otherwise it would require larger inductance. Comparator – a circuit that compares two input voltages Uвх and Uоп; it generates output voltage Uo=Uh, if Uвх ˃Uоп and Uo=Ul if Uвх Uоп, where Uh и Ul - two fixed voltage levels (high and low). U вх U0 U оп Рис. 1.8 To store changing analog signals for the time of conversion, switching and other operations in data collection systems a sample and hold circuit is used _ _ + U1 CН + Управляющее Control voltage напряжение U0