In this workshop, you will learn to use several important, ubiquitous pieces of electronics test equipment. You will use this equipment to complete the Electronics Laboratory Experiment later. The equipment used in this workshop includes a Digital Multimeter (DMM), an oscilloscope (O-scope), a Function Generator (F.G.) and a Direct Current Power Supply (DCPS). You will use these items to generate and measure several common types of electronic signals.
A schematic of an oscilloscope is shown below with its inputs and major controls identified. An oscilloscope in it’s most general use displays the amplitude of an input signal on the vertical axis and the time on the horizontal axis. It is also capable of having the horizontal axis correspond to a second voltage input, though we will not use it as such in this class. The oscilloscope has two inputs that are labeled CH 1 (or X) and CH 2 (or Y) (CH stands for channel). One chooses the input channel for observation using a switch labeled “CH1-Both-CH2.” The scale (volts per graticule division) along the verticle axis is set by the V(olts)/Div switch for the corresponding channel. The position on the display corresponding to zero volts for the vertical axis is adjusted by the Pos(ition) control above the V/Div switch for the CH 1 OR CH 2 input, depending on which channel you wish to observe. The position for the horizontal axis is adjusted by the control above the Sec/Div switch, not by the corresponding control for the X input. The Sec/Div control is adjusted to lower values as the frequency of the input signal increases, in order to display the signal clearly. The intensity of the trace and its focus are adjusted by the controls adjacent to the display above the power-on switch. The oscilloscope can be used to measure either ac or dc signals. It is most commonly used to measure oscillating (repetitive) waveforms and, as is the case in this experiment, compare two or more waveforms.
The three Function controls should all be turned counterclockwise as far as they will go. The waveform (sinusoidal, sawtooth, or square wave) is selected by pushing one of the buttons at the upper right. The frequency is set by selecting a range (using the push buttons at the upper left), and then turning the multiplier dial (left) to get the exact frequency desired. The Wavetek Function Generator has a range of 1 Hz to 2 MHz. After the frequency is set, turn the Amplitude control to set the voltage desired. Pull the amplitude control knob out to set lower voltages; push it in for higher voltages. Make sure the attenuator button (upper right) is “out.” The value of a resistor is color-coded by four bands starting from one end: The value of a capacitor is found in a code printed on the capacitor, consisting of three numerical digits followed by a letter. The first two digits are multiplied by the value represented by the third digit (multiplier), as with resistors. The multiplier values are:
Multiplier Value 0 None 1 10 2 100 3 1000 4 10,000
The resulting value of the capacitor is in picofarads; the letter represents the tolerance of the value. For example, a capacitor with the code 103M would be 10,000 pF, or 0.01 ?F. The letter M represents a tolerance of ?20%.
Resistors: Color Code and measurement with DMM
In your wood block set of electronic components, you will find a number of resistors and capacitors pre-mounted onto banana clips (plastic mounts with two metal connectors sticking out and several holes to accept other, similar connectors). Each one is labeled with the group number (1-8) and a letter. Find resistors P, K, & R. Read the color stripes printed directly onto the component and decipher the value using the color code chart on the bottom of page two of the electronics lab description. Write down your deciphered value for each of the three resistors. Now test each resistor value using your DMM. This can be done by plugging the banana plug directly into the DMM. You can also plug cables into the DMM and use them, as well. (Be careful to get it in the right position and set the front dial to read resistance.)
D.C. Power Supply: Set and Measure using DMM
Locate the D.C. Power Supply and make sure it is plugged in. Power it on and identify the settings, knobs, and display values. Now set the output to +1.5V, +5.0V, and –10.0V and measure each with the DMM using cables. (Be careful to get them in the right position and set the front dial to read D.C. voltage.) Compare the DMM reading with the meter on the front of the power supply.
Function Generator and Oscilloscope Now locate the Function Generator and O-scope. Connect the “Main” output of the function generator to the Channel 1 input of the o-scope. Turn the Channel 1 “Volts/div” knob on the o-scope to 1 (using the x1 indicator on the dial). Set the time scale knob on the o-scope to 1 ms.
Identify the frequency settings on the left side of the F.G.- there are several push-buttons and, on the far left, a fine-adjust dial. Set the frequency range to 10 kHZ with the push-buttons and set the exact frequency to 1.0 (x 10 kHZ) with the dial. On the upper right side of the F.G. depress the push-button indicated with a sine wave. Now locate the “amplitude” knob on the F.G. Make sure it is pushed in for higher voltages, pulled out for lower voltages. Turn this knob to adjust the amplitude of the waveform (as viewed on the o-scope). Note also that there is an “attenuator” push-button in the upper right hand corner. Make sure this is out. (When it’s in, the amplitude is made to be very low voltage. Also make sure that the D.C. Offset knob is pushed in so your waveform should be centered around zero volts.) You should now se several periods of a sine wave on your o-scope. Now set the amplitude to 1.5V peak-to-peak (p/p) using the amplitude knob on the F.G. and monitoring with the o-scope. It will be easier to measure accurately if you expand the wave on the screen. Do this by adjusting the Ch 1 and time settings on the o-scope.
Once this is clear, set the following waveforms while monitoring with the o-scope: Waveform Frequency Amplitude (p/p) sine 10 kHz 2.5 V sine 100 Hz 1.5 V sine 1 MHz 0.5 V square 5 kHz 2.0 V sawtooth 50 kHz 1.0 V Measure the frequency for each by measuring the period of the waveform on the o-scope (note the time per division setting) and using f = 1/T to calculate frequency. How closely is the F.G. dial calibrated? How closely can you measure it? Note your ability to set and measure the amplitude. What aspects limit your accuracy?