Question

1. Why can the DSO only measure node voltages when the Function Generator is the power supply in a circuit (unless it is using a current probe)? 2. Consider Figure 1. According to the calculations in the lab handout, if Z-1kΩ +/6914, then the phase difference (фи-фі) between u(t) and i (t) is 34.6". a. If this v(t) and i(t) were displayed on a DSO (v(t) being a node voltage and using a current probe for i(t) as shown in Figure 6), would i(t) peak to the left or the right of the nearest v(t) peak? b. Determine the time delay At between v(t) and i(t) if f 2kHz. 3. Consider Figure 2. I and V are the phasos for v(t) and i(t) of Figure 1 and problem 2 respectively. I was measured using the current probe as shown in Figure 6. a. Given фи-58" determine фі. b. Determine the resultant фі if the current probe in Figure 6 were reversed. c. Use a straight edge to sketch the resultant / in a well labeled phasor diagram if the current probe in Figure 6 were reversed. An AC voltages and current are sinusoidal waveforms that can be described mathematically as time domain trig functions or as phasors in the phasor domain. For example, consider the voltage and current sketched in Figure 1 for impedance Z. + v(t Figure 1. Impedance Z and its current and voltage drop. time domain phasor domain If passive sign convention is being followed (and it is), then Ohm's Law gives us In general any impedance Z is a combination of following impedances. resistor impedance capacitor impedance inductor impedance The rules for combining impedances are identical to the rules for combining resistances. Note that the capacitor and inductor impedances depend on a(= 2劝. That means impedance is Just a frequency dependent resistance (with units of Ω just like resistance). In the phasor domain these impedances (AC "resistances") are handled exactly the same way in an AC circuit as resistance is handled in a DC circuit. In a nutshell, the circuit analysis toolset you developed for DC circuits-Ohm's Law, KVL, KCL, voltage divider rule, current divider rule, superposition, source transformation, Thevenin's and Norton's equivalent circuits, nodal and mesh analysis - is the same for AC circuits. You just have to get used to dealing with phase constants and j in your calculations. One interesting consequence of Ohm's Law is that knowing an impedance Z tells you immediately the phase difference between the current through Z and the voltage drop across Z (in accordance with passive sign, of course). h4φι lo angle (Z): фи-P1 For example, say you have a lkS2 resistor in series with a 22mH inductor in a 5kHz AC circuit. Being in series means the resistor and inductor impedances add straight up to obtain the equivalent impedance. z 1 + j (2n) (5kHz) (22mH) Z 1.216k0234.6° фи-ф,-34.6" DSO + probe lead DMM probe leacd (black allegator clip) oV ref Earth Ground Figure 3. The -leads of the DSO voltage probes used in lab are common (connected) to the Function Generator's-lead via the Ground Plugs of their power cables. The difference between the DMM and DSO is that as far as the DMM Voltmeter is concerned the 0V reference node can be any node in the circuit. In the AC circuits you build in this lab, the FG's negative is always designated the 0V reference and the negative of a DSO voltage probe should only be connected to this 0V reference. Although the DSO's in lab are only designed to measure node voltages when using the Function Generators, there is an add-on that can allow the DSO to measure currents in a circuit, at least indirectly. This device is called a current clamp. The ones used in lab are gure 5 lists some of the controls on the CP62 that need to be understood when using this current probe. Control/Indicator Current flow symbol. The arrow shows the probe's polarity convention for measuring current flowing from positive to negative. Zero adjustment. Rotate to adjust the probe output to zero when there is no current present. It may also be used to offset a DC signal component. Zeroing is not needed for AC measurements unless your instrument cannot isolate a DC component (if present) ZERO ADJUST 100 mVIA 10 mVIA OFF OFF/Range switch. Slide the switch from OFF to either the 10 mVIA or 100mVIA range. When either range is selected, the probe is turned on, and the green battery indicator lights. If the indicator does not light, see Battery Notes and Battery Installation on page16. Figure 5. Controls on the CP65 current probe. at the CP62 current probe does is convert a current in a wire to a voltage that can be layed on the DSO. As seen in figure 4 given above, the CP62 current probe is a current np. The "trigger" on the probe opens the "jaws" of the clamp and a wire carrying the curr want to measure in the circuit is placed in the clamp (see Figure 6). The zero adjust is us re energizing the circuit to zero out any ambient DC magnetic fields near the probe. example, say you want to use the current probe to display the current through an imped fter connecting the probe's BNC cable to one of the DSO's input channels, the first st i(t) Figure 6. Measuring current i(t) through impedance Z. There is an arrow (the "Current Flow Symbol") stamped on the side of the probe as indicated here. If the arrow "Current Flow Symbol") stamped on the side of the clamp is reversed, your measured i(t) will be 180° out of phase with what you expect it to be. You need to be aware of the arrow for the same reason you need to be aware of the t probe leads when using the DMM to measure a current. Next, set the Range Switch on the probe to 10 mV 100A This does two things: it powers up the current probe and sets the probe's sensitivity or conversion factor. By the way, a 9V wall transformer (AC to DC converter) is the power supply for the current probes used in lab. For example, say you have clamped the current probe as described above onto a wire and you have set the Range Switch to 10 In Channel 1 of the DSO you have the FG supply voltage to give you a time reference and in Channel 2 you have the current probe output. Your DSO display gives you the traces vi and v2 shown in Figure 7

Answer 1

3 4. C it lie | U ck) Cぐ

2 34.C 23. 58 29 4 180 23.4 203-4 ウ 23.4- 58 = 145.4
1)DSO has a Cathode ray oscilloscope which is essentially a voltmeter.For other functionality ,like current,phase etc. we need transducer to convert them into voltages.So DSO originnaly is a voltmeter and is operated in voltages.