Digital_Data_Acquisition

# Digital_Data_Acquisition - Digital Data Acquisition Author...

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Digital Data Acquisition Author: John M. Cimbala, Penn State University Latest revision: 27 July 2007 Introduction Instruments and data can be either analog ( continuous ) or digital ( discrete ). In this learning module, we discuss digital data, and how to convert between analog and digital signals. Review - Decimal to Binary Conversion While we are used to working with decimal numbers ( base 10 ), computers and many modern instruments and electronic devices use binary numbers ( base 2 ). Decimal numbers contain the digits 0 through 9, while binary numbers contain only digits 0 and 1. As a review, here is a listing of the first eight (including zero) decimal and binary numbers: Decimal number Binary number 0 0 1 1 2 10 3 11 4 100 5 101 6 110 7 111 There are simple techniques to convert from decimal to binary and vice-versa: o Decimal to binary : ± Successively divide by 2, as in the following example: convert the decimal number 29 into binary: Value/2 Integer value Remainder 29/2 = 14 + 1 /2 14 1 14 /2 = 7 + 0 /2 7 0 7 /2 = 3 + 1 /2 3 1 3 /2 = 1 + 1 /2 1 1 1 /2 = 0 + 1 /2 0 1 Read this way, bottom to top. ± The binary number is obtained from the “remainder” column, reading from bottom to top ( backwards ); the answer is 11101 . o Binary to decimal : ± Add up each non-zero bit, from left to right, converting the binary number 11101 into decimal: Bit considered (underlined) Value of the place Value of the bit 11101 1 1 × 1 = 1 1110 12 0 × 2 = 0 111 01 4 1 × 4 = 4 11 101 8 1 × 8 = 8 1 1101 16 1 × 16=16 ± The decimal number is obtained by summing the “Value of the bit” column; the answer is 29 . Example : Given: The decimal number x = 4 To do: Convert x to a binary 4-bit number. Solution: We use the technique of successive division by 2, as per the following table: Read this way, bottom to top. Sum this column. Value/2 Integer value Remainder 4 /2 = 2 + 0 /2 2 0 2 /2 = 1 + 0 /2 1 0 1 /2 = 0 + 1 /2 0 1 The resulting binary number is read from the bottom to the top, 0100 x = in binary form. We have added a leading zero so that the result is a 4-bit number. If we were asked for 8 bits, we would write x = 0000 0100. Some calculators have built-in binary-to-decimal and decimal-to-binary converters.

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Analog to Digital Conversion (A/D conversion) Digital data acquisition is used in digital multimeters, digital oscilloscopes, computer-controlled data acquisition systems, and many other modern instruments and electronic devices such as cell phones. In all these examples, the conversion of an analog signal into a digital signal is accomplished with an electronic device called an analog-to-digital converter , which we abbreviate A/D converter . The goal of an A/D converter is to change an analog voltage signal into a digital number (in binary form). An A/D converter is labeled as N -bit, where the number of bits N represents how many bits (ones and zeroes) are used in the digital output of the A/D converter . E.g., an 8-bit converter creates an 8-bit output.
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Digital_Data_Acquisition - Digital Data Acquisition Author...

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