Introduction
Instrumentation used in chemical analyses incorporate a variety of electronic components used to manipulate the signal from the analyte. While instruments can often be treated as "black boxes", an understanding of some of the fundamental aspects of their operation can prove to be invaluable in order to make full use of the equipment.
Theory and background information for this lab can be found in Chapter 2 of Skoog, Holler, and Nieman, fifth ed., and also in the lecture material.
Equipment
The following items are required for this laboratory:
(1) Two resistor decade boxes
(2) Capacitors of various values
(3) A small dc power supply
(4) Digital voltmeter (DVM)
(5) Function generator
(6) Hook-up wire
(7) Oscilloscope
Procedure
I. Series and Parallel Circuits
Configure the two decade boxes such that both read 5k. Place them in
series with the dc power supply as is shown in the diagram below:
DO NOT TURN ANYTHING ON YET!!
A. Have the instructor configure the DVM to measure resistance and make the following measurements:
1. Measure and record the resistance across R1 and R2
individually.
2. Measure and record the total resistance across both resistors.
How is this resistance related to the values of the individual resistors
in this circuit?
B. Have the instructor reconfigure the DVM to measure dc voltage and set the power supply to output approximately 10 volts. Make the following voltage measurements:
1. Measure and record the voltage drop across R1 and R2
individually.
2. Measure and record the total voltage drop across both resistors.
How is this voltage related to the voltage drops across each resistor in
this circuit?
C. Reconfigure the DVM to measure current.
1. Measure and record the current supplied by the power supply.
2. Measure and record the current flowing through each resistor. What
is the relationship between these currents and the current supplied by
the power supply?
Turn the power supply off. Configure the two decade boxes such that both read 5k. Place them in parallel with the dc power supply as is shown in the diagram below:
DO NOT TURN ANYTHING ON YET!!
D. Configure the DVM to measure resistance and measure the total resistance across both resistors. How is this resistance related to the values of the individual resistors?
E. Reconfigure the DVM to measure dc voltage and set the power supply to output approximately 10 volts. Make the following voltage measurements:
1. Measure and record the voltage drop across R1 and R2
individually.
2. Measure and record the total voltage drop across both resistors.
How is this potential related to the voltage drop across each resistor?
F. Reconfigure the DVM to measure current.
1. Measure and record the current supplied by the power supply.
2. Measure and record the current flowing through each resistor. What
is the relationship between these currents and the current supplied by
the power supply?
II. Voltage Dividers
A. With the power supply turned off, assemble a circuit using the two decade boxes which will divide the output of the power supply by a factor of 10. You will need to calculate the individual resistances required. Show these calculations and state the values of the resistors.
B. Sketch your circuit and show where the factored voltage occurs.
C. Set the power supply to several voltages and test that your voltage divider functions. Record all data.
III. Filters
A. Using the variable capacitor, one of the decade resistor boxes, the function generator, and the oscilloscope, construct a circuit which will function as a low-pass filter with a gain of 0.5 at 1 kHz. Record the values of the capacitance and resistance which were used and show all calculations.
B. Using the oscilloscope, observe the filtered and unfiltered waveforms at several frequencies. Note any significant differences.
C. With the DVM set to measure ac voltage, confirm that the gain of this filter is indeed 0.5 at 1 kHz. Also record the gain of this filter at several frequencies around 1kHz.
D. Using the DVM, measure the gain of the filter at several frequencies ranging from 10 Hz to 100 kHz. Obtain enough data to construct a gain diagram for this filter.