Chem 498A/C Fall 1997
Name _______________________________________
Time limit: 2 hours.
1. a. What resistance will be measured in the following circuit from
point A to point B (i.e. if an ohmmeter is connected between point A and point
B)?
b. If a battery is connected between points A and B, which single
resistor in the above circuit has the largest voltage across it?
c. In the following circuit, which single resistor has the largest
current flowing through it? Explain your reasoning.
2. Suppose you need a line-operated regulated power supply that is
capable of supplying 5 volts DC with both line and load regulation for load
currents from 0 to 100 mA. You have on hand a power transformer with a 115 VAC
primary and a 6 VAC secondary, a large number of rectifier diodes (1 amp
current rating, 100 volt peak reverse breakdown voltage), a 2000 µF
electrolytic filter capacitor, a 5 volt, 5 watt Zener diode, and a full supply
of resistors in all standard values up to 5 watts power dissipation. Design
and draw the schematic diagram of a circuit that will meet the above
requirements.
3. In the following Wheatstone bridge, all the resistors are 100 Ohms , M is a voltmeter whose input resistance is very much higher that 100 Ohms , and the battery supplies 12.0 volts.
If the voltmeter can detect a minimum voltage change of 1 mV, then what is the smallest resistance change in R_{4} (in ohms) that could be detected, assuming that the other 3 resistors do not change?
4. When planning to acquire data from an instrument into a computer, how do you determine when to use an RS-232 interface and when to use a analog-to-digital converter?
5. Suppose an instrument 's analog output has a 0 - 100 mV DC voltage range and an output resistance of 1000 ohms. You want to digitize this signal with a CIO-AD08 12-bit ADC that has a 0 - 5 volt range with full 12-bit full-scale resolution?. Design a circuit that will accomplish this, showing all component values.
6. In the lab you used this QuickBASIC program to read the CIO-AD08 12-bit ADC in the IBM-PC:
7. (a) In the digital signal processing exercise (using SPECTRUM), for what purposes did you utilize the fourth derivative operation?. What is the relationship between the amplitude of the n^{th} derivative of a peak-shaped signal (e.g. Gaussian or Lorentzian peak) and its (b) peak height and (c) peak width?
8. In the experiment involving the stepper motor connected to the monochromator, what is the purpose of the transistor switches between the computer's digital outputs and the remote inputs of the stepper controller box? That is, why not connect the computer and the controller box directly without the transistor switch?
9. Explain the operation of the following program, assuming that it runs on a computer that is correctly hooked up to a PROTEK digital multimeter that has been set to RS-232 and the temperature mode.
DIM temp(1000) DIM time(1000) TIMER ON interval=10 OPEN "com1:1200,E,7,1" AS #1 ON TIMER(interval) GOSUB TakeReading j =0 repeat: key$=INKEY$ IF j=1000 THEN GOTO done IF key$<>"q" THEN GOTO repeat done: FOR k=1 TO j PRINT time(k), temp(k) NEXT k END TakeReading: PRINT #1," " INPUT#1,A$ j=j+1 time(j)=TIMER temp(j)= VAL(MID$(A$,6,4)) RETURN
10. Suppose you are measuring a signal with the Vernier Universal Lab Interface and Data Logger software, like you used in the laboratory, to digitize and record the signal from some instrument.
b. Is there any disadvantage to use the largest available data rate and time axis range available?