mt_sol

# mt_sol - Name Solution Real Time Computing Systems EE 4770...

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Name Solution Real Time Computing Systems EE 4770 Midterm Examination 17 March 1999, 8:40-9:30 CST Alias Problem 1 (50 pts) Problem 2 (50 pts) Exam Total (100 pts) Good Luck!

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Problem 1: The partially designed circuit below is to be used to convert temperature x [ - 20 C , 40 C] to a ﬂoating-point number H ( x )= x/ K to be written into variable temp . The circuit uses an RTD, its model function is H t1 ( x )= R 0 (1+ α 1 x ), where R 0 = 100 Ω and α 1 =0 . 00398 / C. The RTD is connected to a - 7V source as shown. The ADC response is H ADC(10V , 16b) . + - v 1 v 2 R 2 R 3 -7 V ADC B I RTD ( a ) Complete the design (choose values for v 2 , R 2 and R 3 ), so that the ADC input is in [0 . 5V , 9 . 5V] over the range of temperatures to be measured. (20 pts)(For reduced credit [ < 20 pts] make full use of the ADC dynamic range.) First, ﬁnd the voltage at the ADC input: H c ( H t1 ( x )) = - R 3 ± v 1 H t1 ( x ) + v 2 R 2 ² Call the resistance at the minimum temperature R min and the resistance at the maximum temperature R max .U s i n g the boundaries of the temperature range R min = H t1 ( - 20 C) = 92 . 04 Ω and R max = H t1 (40 C) = 115 . 92 Ω . As stated in the problem, the ADC input should be a minimum of 0 . 5V this occurs at the maximum temperature: H c ( H t1 (40 C)) = 0 . 5V= - R 3 ± v 1 R max + v 2 R 2 ² . Similarly the ADC input must be 9 . 5V at - 20 C or H c ( H t1 ( - 20 C)) = 9 . 5V= - R 3 ± v 1 R min + v 2 R
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## mt_sol - Name Solution Real Time Computing Systems EE 4770...

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