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Fe_sol - Name David M Koppelman Real Time Computing Systems EE 4770 Final Examination 15 May 1998 17:30-19:30 CDT Problem 1 Problem 2 Problem 3

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Name David M. Koppelman Real Time Computing Systems EE 4770 Final Examination 15 May 1998, 17:30-19:30 CDT Alias The Solution Problem 1 (30 pts) Problem 2 (30 pts) Problem 3 (20 pts) Problem 4 (20 pts) Exam Total (100 pts) Good Luck!
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Problem 1: Precise temperature measurements over a 3 C range are to be made using a thermis- tor. Though the range is 3 C, it can fall within 250 K to 350 K, that is, it might be [250 K , 253 K] for one set of measurements and [302K , 305 K] for another. Design a circuit to convert the temper- ature, x [250 K , 350 K], into floating point number H ( x )= x/ Ktobewr ittentovar iab le tee so that two consecutive measurements that fall within a 3 C range are made precisely, as described below. To achieve the high precision over a narrow range the circuit will use an instrumentation amplifier with an adjustable gain and a digital-to-analog converter (DAC) as a bias source, as shown below. The gain of the amplifier is set to i × a 1 from the interface routine by calling setGain(i) ,where i [1 , 256] and a 1 is a chosen value for the amplifier. The voltage is set to j × v 2 by calling setVolt(j) j [0 , 2 16 - 1] and v 2 is another chosen value. See the sample code below. The thermistor has model function H t2 ( T R 0 e β/T β = 3000 K and R 0 =0 . 059Ω. The circuit uses a 16-bit, 10-volt ADC. Resistor R = 9289 Ω and voltage source v A = - 10 V. Except for a 1 and v 2 the circuit is already designed. Do not find values for R and v A , use the values specified above. For partial credit find an interface routine (to write tee ) assuming a fixed gain for the instrumentation amplifier (choose a convenient value) so that the entire temperature range can be measured ([250 K , 350 K]). Also choose a convenient value for v - . For full credit the interface routine must provide the high precision for small changes from call to call. The routine should remember the previous gain and bias setting used. If the current temperature can be measured using those values they won’t be changed before reading the temperature. If the temperature can’t be measured (it falls outside of the range previously used) new gain and bias values should be chosen so that the current temperature is at the center of a new 3 C range (or as close as possible), and the temperature should be measured using the new values. (The ADC output is zero for negative values and is 2 16 - 1 for values above 10 volts.) Be sure to provide values for a 1 and v 2 .(30p t s ) ADC DAC + - + - v A R j v 2 (voltage) j i i a 1 /* Sample code. */ setGain(3); /* Set amp gain to 3 * a_1 */ setVolt(4); /* Set DAC output to 4 * v_2 */ r=readInterface(); /* Read ADC output. . */ Use next page for solution, schematic and data repeated. 2
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Problem 1, continued. The thermistor has model function H t2 ( T )= R 0 e β/T ,where β = 3000 K and R 0 =0 . 059Ω. The circuit uses a 16-bit, 10-volt ADC. Resistor R = 9289 Ω and voltage source v A = - 10 V.
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This note was uploaded on 11/28/2011 for the course EE 4770 taught by Professor Staff during the Fall '99 term at LSU.

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Fe_sol - Name David M Koppelman Real Time Computing Systems EE 4770 Final Examination 15 May 1998 17:30-19:30 CDT Problem 1 Problem 2 Problem 3

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