Chem 8153 January 2009 1 Laboratory 1 Measuring Devices: DMM and Oscilloscope The objectives of this laboratory session are: (1) Learn the proper use of equipment that will be used throughout the semester. (2) Determine the load resistance of a digital multimeter (DMM) or an oscilloscope. (3) Measure the properties of sine and square waves. (4) Practice trouble shooting circuit measurements. Introduction Most of the laboratory experiments will use a Proto-board PB-503. It is a large breadboard area and a wide choice of built-in circuit accessories allow rapid and accurate construction of virtually any type of analog or digital circuit. In this laboratory, we will test that the board’s function generator, the DC power supplies, and the potentiometers of this are working properly. We will also assemble on the board a basic circuits to determine the load resistance of a DMM and an oscilloscope. Lastly, we will use an oscilloscope to measure the properties of sine and square waves generated by the function generator in the Proto-board. Prelab Prior to this lab session, read the Proto-Board instruction manual and (ii) the article, “Understanding Oscilloscope Probes” (Gordon, J., Radio-Electronics, Jan 1989, 46-51); understand probe circuits (see Part B of the experiment); do calculations in Part C of the experiment. During the first 15 minutes of the laboratory period, the TA (or instructor) will provide a basic explanation on the use of the Proto-Board, oscilloscopes, and DMM. Components and Equipment Needed (See pictures in the following page) 1. DMM 2. Proto-Board 3. Oscilloscope and probes 4. Resistors 5. Jumper wiresChem 8153 January 2009 2 Digital Multimeter (DMM) Function Generator Resistor Probe Protoboard/breadboard with a simple circuit Oscilloscope with a probeChem 8153 January 2009 3 A. Testing some Proto-Board components (Always turn off proto-board the Proto-Board when making connections. It will protect you and the electronic components). Power sources. Use the Fluke digital multimeters (DMM) to measure the actual voltage supplied by the +/- 15 V sources. With a screwdriver, change the voltage of these supplies and observe with a Fluke DMM. Ultimately, set each to +/-15 V. Function generator. The multi-waveform function generator provides a continuously variable frequency signals from 0.1 to 100kHz (radio frequency). Connect its output to one of the speaker inputs. Switch the generator to the 100X position and move the frequency control to the maximum. Move the amplitude control upward until you hear an audible tone coming from the speaker. Test the various waveforms (sine, square, triangle, and TTL). Changing the frequency control should vary the pitch of the tone. Potentiometers. The Proto-Board has a 1 K! and a 10 K! potentiometer. Using an ohmmeter confirm that the resistance between the variable contact (position 2) and either positions 1 or 3 varies when your rotate the potentiometer knob. Also, confirm that the resistance between positions 1 and 3 is constant regardless of the position of the knob. Report. In your report include the Proto-Board model. State briefly whether or not each of the components above are working correctly. Include quantitative information (e.g. maximum and minimum resistance of the potentiometers) when available. These are important specifications of the Proto-Board that you will be using in other experiments. B. Measuring a sine and a square wave Introduction. Oscilloscopes are commonly used to measure AC signals. There are two different types of oscilloscopes in this lab—Tektronix and Gould. Manuals are available for each. These should be consulted as you familiarize yourself with the basic controls. There are three methods of connecting an oscilloscope to the signal: a simple wire lead, coaxial cable, and scope probes. A simple lead wire may be sufficient when the signal level is high and the source impedance low, such as transistor-transistor logic (TTL) circuitry, but is not often used. Unshielded wire picks up hum and noise; this distorts the observed signal when the signal level is low. Also, there is the problem of making secure mechanical connection to the input connectors. A binding post-to “baby N” connector (BNC) adapter is advisable in this case (BNC = Bayonet Neill Conselman) . Coaxial cable is the most popular method of connecting an oscilloscope to signal sources and equipment having output connectors. The outer conductor of theChem 8153 January 2009 4 cable shields the central signal conductor from hum and noise pickup. These cables are usually fitted with BNC connectors on each end, and specialized cable and adaptors are readily available for mating with other kinds of connectors. Scope probes are the most popular methods of connecting the oscilloscope to circuitry. See These probes are available with 1! attenuation (direct connection) and 10! attenuation. The 10! attenuator probes increase the effective input impedance of the probe/scope combination to 10 M" shunted by a few picofarads. The reduction in input capacitance is the most important reason for using attenuator probes at high frequencies, where capacitance is the major factor in loading down a circuit and distorting the signal. Despite their high input impedance, scope probes do not pick up appreciable hum or noise because the outer conductor of the probe shields the central signal conductor and is always at ground. Procedure. Use a function generator to generate a sine wave and a square wave and to observe its properties with an oscilloscope. Adjust (compensate) the probes. Determine the period, amplitude, rise time, and wave shape. The detailed procedure follows. a. Input the AC signal (sine or square wave) from the Proto-Board. Experiment with different frequencies and amplitudes. Experiment with the trigger controls and with the AC/DC coupling in the oscilloscope (check the oscilloscope manual). Make sure that you are able to determine the amplitude, peak-to-peak voltage, and frequency of a wave. b. Adjust (compensate) your scope probes as