Table of Contents 1.0 Introduction to VirtualBench ............................................................................................................................................ 3 1. 1 VirtualBench in the Laboratory .................................................................................................................................... 3 1.2 VirtualBench Specifications....................................................................................................................
1.0 Introduction to VirtualBench VirtualBench is a radically practical approach to instrumentation. By combining the most essential instruments into one device, VirtualBench integrates with PCs and tablets to offer a convenient yet powerful solution for measurement and instrumentation. It opens up new possibilities for how engineers can interact with and automate benchtop test equipment through an intuitive user interface that works across the PC and iPad.
1.2 VirtualBench Specifications Note: Find detailed specifications in the specification document. Refer to this document for triggering options, USB and wireless connectivity, calibration information, and operation/safety requirements. Specifications are valid following 30 minutes of warmup and for a typical temperature of 25 °C unless otherwise noted. The following sections offer a quick overview of the hardware specifications for the various VirtualBench instruments. 1.2.
1.2.2 Function Generator Figure 1.3. Function Generator ● ● ● Channels: 1 Waveforms: Sine, square, triangle, and arbitrary Update rate: 125 MS/s 1.2.3 Digital I/O Figure 1.4. Digital I/O ● ● Channels: 8 Logic Level o Input: 5 V TTL o Output: 3.
1.2.4 Digital Multimeter Figure 1.5. Digital Multimeter ● ● ● Functions: AC/DC voltage, AC/DC current, resistance, diode Resolution: 5½ digits Sample Rate: 5 S/s 1.2.5 DC Power Supply Figure 1.6.
1.3 Introduction to VirtualBench Getting Started Guide Lab Exercises The VirtualBench Getting Started Guide includes three example exercises to help you learn the basics of VirtualBench and integrate its unique capabilities into your laboratory. These three exercises, outlined below, are common in an introductory analog circuits class. Note that these exercises are designed to help you gain a better understanding of how to operate the VirtualBench device.
2.0 Using the Digital Multimeter and Function Generator VirtualBench includes a 5½-digit digital multimeter (DMM), which is capable of taking voltage, resistance, and current measurements, as well as a function generator (FGEN) that can output both AC and DC signals. In this section, use both the DMM and FGEN to explore taking power measurements of a resistive circuit. Learning Objectives: You will understand these core concepts for VirtualBench after completing the activities in this chapter: 1.
In this circuit, you have several resistors in a series parallel combination. Though you can calculate the effective resistance of the circuit, you would find it tedious, especially when you have to consider the tolerance values of each resistor. Instead, use the DMM to measure the total resistance of the circuit as show in Figure 2.2. Figure 2.2.
Figure 2.3a. Multisim Circuit Simulation With DC Voltage Measurement Figure 2.3b.
Once you have both your voltage and resistance measurements, you can then calculate power using the formula below: where P represents power, V represents the measured voltage, and R is the measured resistance. Table 2.1 lists your results based on the circuit in Figure 2.3. Voltage Source Measured Voltage Measured Resistance 5 Vdc (DC) 5 Vpp at 60 Hz (AC) 5 Vdc 176.85 Ω 1.768 Vrms 176.85 Ω Table 2.1. Multisim Circuit Simulation Results Average Power 141 mW 17.7 mWrms 2.
Figure 2.4a. Resistor Network Schematic: XMM1 Represents the DMM and XFG1 Represents the FGEN Figure 2.4b.
Figure 2.5. Physical Circuit Connections to VirtualBench Run the VirtualBench Application Follow these steps to use the VirtualBench device to measure resistance, DC voltage, and AC voltage. Exercise 2.1: Measuring Resistance 1. To take your resistance measurement, first disconnect the positive and negative leads of the FGEN from your resistor network as shown in Figure 2.6. Figure 2.6.
2. Configure the DMM to take resistance measurements. First set the DMM measurement mode to “Resistance.” After setting the measurement mode, next you need to set the range of the measurement; if the range is too small, your results will be railed, but if the range is too large, your results might not have enough precision. From the simulation results in Table 2.1, you know that the total resistance is around 175 Ω; therefore we need to set the range to 1 kΩ. Figure 2.7 shows the DMM configuration.
Figure 2.8. FGEN Configured for DC Voltage With 5.00 Vdc Offset 3. Configure the DMM to take a voltage measurement. Set your DMM measurement mode to “DC Voltage.” After setting the measurement mode, you will need to set the resistance. From the simulation results in Table 2.1, you know that the voltage should be around 5 V. Therefore, set the range to 10 V, which allows you to capture the measurement without any voltage saturation.. Figure 2.9 shows the DMM with the proper mode and range configured.
Figure 2.10. FGEN Output Enabled 5. Measure the voltage by connecting the positive probe to the positive lead of resistor R1 and the negative probe to the negative lead of resistor R10 (refer to Figure 2.5 for connections). This measures the voltage drop across the entire circuit. Record your measured voltage in the field below. a. Total DC Voltage Drop (measured):_______________________ 6. After taking the voltage measurement, turn off the FGEN by pressing the power button to disable the output.
1. The VirtualBench FGEN can output ±12 Vpp at a maximum frequency of 20 MHz. In this exercise, use the FGEN to output an AC sine wave with 5 Vpp at 60 Hz with no DC offset voltage. Figure 2.11 shows the FGEN with these settings configured. Figure 2.11. FGEN Configured for 60 Hz, 5 Vpp, 0 DC Offset, Sine Wave 2. Now change the DMM measurement mode from DC Voltage to AC Voltage. This configures the DMM to take RMS measurements instead of regular averaging.
5. Disable the FGEN output. Exercise 2.4: Calculating Power Using the equation for power and your results from the previous exercises, calculate the power drawn by the circuit when using a DC and an AC signal source. Fill in Table 2.2 with your results. Voltage Source DC signal source AC signal source Measured Voltage Measured Resistance Average Power Table 2.2. Measured Circuit Results Recall that at the beginning of this section, you saw a similar table using a simulated circuit.
Voltage Source DC signal source AC signal source Simulated Voltage Measured Voltage Simulated Resistance Measured Resistance Simulated Average Power 5V 3.909 V 176.85 Ω 176.6 Ω 141 mW 1.768 Vrms 1.381 Vrms 176.85 Ω 176.6 Ω 17.7 mWrms Table 2.3. Observed Measurements Versus Simulated Measurements Measured Average Power 86.5 mW 10.8 mWrms Table 2.3 compares the simulated results versus some test measurements. As expected, the measured results match the expected results.
Figure 2.15. Circuit Model Corrected for FGEN Output Impedance Just considering the case where you used a DC signal source, you can now simulate the circuit again. Figure 2.16 shows the results of your new circuit model. Figure 2.16. DC Voltage Measurements of the Corrected Circuit Model From Figure 2.16, you can see that you now measure 3.898 V across your simulated circuit, which is much more aligned with the measurements that you took with the DMM (3.909 V).
Figure 2.17. AC Voltage Measurements of the Corrected Circuit Model Table 2.4 shows the simulated measurements of the corrected circuit and your actual measurements side by side. The measurements are now closer to what you expected to see. If you would like to verify these results for yourself, please use the VirtualBench Section 2_DMM and FGEN Resistor Network Corrected.ms13 file. Voltage Source DC signal source AC signal source Measured Voltage Simulated Voltage (Corrected) 3.909 V 3.898 V 1.
3.0 Function Generator and Mixed-Signal Oscilloscope VirtualBench contains both a function generator (FGEN), which is capable of producing standard patterns such as sine, triangle, and square waves, as well as a mixed-signal oscilloscope (MSO), which can capture acquired records of various waveforms. The FGEN is capable of producing sine waves with a frequency of up to 20 MHz at a maximum voltage of 12 V into a high-load impedance.
Figure 3.1. Multisim Non-inverting Amplifying Circuit In Figure 3.1, you can see a positive and negative power supply, which is necessary to allow the op-amp circuit to provide a negative voltage at its output. You can also see that the circuit has two resistors: R1 (1 kΩ) and R2 (100 Ω). As configured, this op-amp should present a voltage at its output (V Out) that is (1+ R1/R2) times greater than the voltage at input (V In).
Figure 3.2. Multisim Oscilloscope Capture and Results for Amplifying Circuit In Figure 3.2, the peak voltage read at Channel_A is the input voltage with a value of 98.125 mV. This value is not quite the 100 mV peak you specified because Multisim takes into account a small voltage drop at the scope input. Also see that Channel_B contains a peak voltage of 1.080 V. This represents the voltage at V Out. When you divide 1.080 V by 98.125 mV, you get 11.006.
Figure 3.3. Multisim RC Circuit In this circuit, the FGEN output is a square wave with an amplitude of 5 V and a frequency of 100 Hz. At the output of the FGEN, there is a 1 kΩ resistor in series with a 1 µF capacitor. This series RC circuit increases the time constant of the circuit. This means that the 10%-90% rise time of the square waveform, as measured across the capacitor, will be increased. The time constant, τ=RC, of this circuit has a value of approximately 1 ms.
Figure 3.4. Multisim Oscilloscope Capture and Results for RC Circuit As shown in Figure 3.4, you can use horizontal cursors T1 and T2 to find the 10% and 90% levels on Channel B as accurately as possible. Since the maximum level is 5 V, these values should be 500 mV and 4.5 V, respectively. However, because the scope horizontal resolution is limited, you had to align the cursors as close as possible to these values at 558.929 mV and 4.490 V.
3.2 Component Demonstration Follow these steps to use the VirtualBench FGEN and MSO to implement the previous simulated circuits in real life. Build the previously investigated circuits (figures 2.1 and 2.3) to do this.
Connect the V_POS (pin 7 of op-amp) to the +25 V supply of the VirtualBench power supply (red wire on breadboard) Connect the V_NEG (pin 4 of op-amp) to the -25 V supply of the VirtualBench power supply (light green wire on breadboard) Connect the GND of the ±25 V supply to the ground of amplifier circuit (black wire on breadboard) Place R1 (1 kΩ) between V Out (pin 6 of op-amp) and pin 2 of the op-amp (teal and purple jumper wires on breadboard) Place R2 (100 Ω) between junction connecting R1 to
Figure 3.6b. Breadboard Layout for Amplifier Circuit Figure 3.7.
2. Launch the application. 3. Enable channels 1 and 2 of the MSO by clicking the square icons next to the channel names. Set the vertical settings for each channel to 500 mV/div. Figure 3.8. Disabled MSO Inputs (left) and Enabled Inputs (right) 4. Configure the MSO to have Normal record acquisition and set the horizontal timing to 10 ms/div (both shown in Figure 3.9). Configure the Trigger Type to Edge, the Channel Source to 1, and the Edge Detection to Rising (as shown in Figure 3.10).
Figure 3.11. Configuring MSO Trigger Level 5. Turn on the DC power supply outputs by clicking the on/off button at the bottom of DC power supply segment. Configure the -25 V supply to supply -5 V. Configure the +25 V supply to supply 5 V. Set the current outputs on both supplies to 0.5 A. Figure 3.12. Configuring DC Power Supply 6. Turn on the FGEN output by clicking the on/off button at the top of the FGEN segment. Set the output frequency to 100 Hz. Set the amplitude to 0.
Figure 3.13. Configuring Function Generator 7. You should now see that there are two signals in the MSO display. The channel 2 signal should be higher than the channel 1 signal. Verify that your signals look like the ones in Figure 3.14.
Figure 3.14. MSO Display With Signals Active 8. Now that you have achieved the two signals you were looking for, you need to configure measurements on the two signals. Select the icon in the MSO display that looks like a meter stick to choose which measurements to perform on the waveforms acquired by the MSO. Figure 3.15.
9. In the Measurements toolbar, configure Amplitude and High measurements under the Voltage category for both channels 1 and 2. Once you have selected these items, they should remain visible at the bottom of the MSO display until you deselect them. Figure 3.16. Configuring Amplitude Measurements on Both Channels 10. Make note of the amplitudes for channels 1 and 2 as well as the highs for channels 1 and 2. Divide the amplitude on channel 2 by the amplitude on channel 1. a.
12. Export the VirtualBench data to a .CSV file by clicking the “Export Data” icon shown in Figure 3.18. Alternatively, you can export the data by navigating to File»Export Data. Figure 3.18. Export Data Icon Expected Results In theory, you should have expected an analog gain of exactly 11, according to the equation for op-amp gain. This should remain true whether you are generating a sine, square, or triangle wave.
Exercise 3.2: Building the RC Circuit and Measuring 10%-90% Rise Time of Waveforms 1. Configure the breadboard layout and VirtualBench connections for the RC circuit as explained below. Refer to the schematic diagram and example breadboard layout (Figure 3.19) as well as the example connections to VirtualBench (Figure 3.20). Figure 3.19a. RC Circuit Schematic Figure 3.19b. Breadboard Layout for RC Circuit The RC circuit requires the following connections to the VirtualBench device (Figure 3.
Figure 3.20. Physical Circuit Connections to VirtualBench for RC Circuit 2. Launch the VirtualBench application. 3. Enable channels 1 and 2 of the MSO by clicking the square icons next to the channel names. Set the vertical settings for each channel to 5 V/div. Configure an offset of 7.5 V for channel 1 and an offset of -7.5 V for channel 2.
Figure 3.21. Configuring Vertical Settings for MSO 4. Configure the MSO to have Normal record acquisition once a trigger is received. Also set the Horizontal timing to 10 ms/div. Configure the Trigger Type to Edge, the Channel Source to 1, and the Edge Detection to Rising. Also set the Trigger Level to 1 V.
Figure 3.22. Configuring MSO Horizontal and Trigger Settings 5. Turn on the FGEN output by clicking the on/off button at the top of the FGEN segment. Set the output frequency to 100 Hz. Set the amplitude to 5 Vpp, the DC offset to 0 V, and the duty cycle to 50%.
Figure 3.23. Configuring FGEN 6. You should now see that the MSO display contains two signals. The signal for channel 2 should be distorted compared to the channel 1 signal. Instead of appearing as a clean square wave, it is rounded.
Figure 3.24. MSO Display With Signals Active 7. Now that you have achieved the two signals you are looking for, you need to configure measurements on the two signals. Again, do this by selecting the icon in the MSO display that looks like a meter stick (as in Figure 3.15). 8. In the Measurements toolbar, configure a Rise Time measurement under the Time Category for both channels 1 and 2. Once you have selected these items, they should remain visible at the bottom of the MSO display until you deselect them.
Expected Results In theory, you should have expected a 10%-90% rise time of 0 s on the input signal from the FGEN (channel 1). You should have also read a 10%-90% rise time that is approximately 2.2 ms as measured across the capacitor (channel 2). Observed Results In reality, you got something close to the expected value for 10%-90% rise time as measured across the capacitor (channel 2). Of course, your observed value was not exactly 2.
4.0 Programmable DC Power Supply VirtualBench includes a programmable DC power supply with three independent channels capable of providing 0 V to 6 V at 1 A, 0 V to 25 V at 500 mA (isolated), and 0 V to -25 V at 500 mA (isolated). You can modify the power levels of each channel through the VirtualBench application or the NI-VirtualBench driver API. Figure 4.1 shows the VirtualBench DC power supply connector. Figure 4.1.
Figure 4.2. Multisim Circuit Simulation Figure 4.3.
4.2 Component Demonstration Follow these steps to demonstrate the correct operation of an op-amp and the VirtualBench DC power supply, function generator (FGEN), and mixed-signal oscilloscope (MSO). Parts List ● One UA741CN op-amp ● One breadboard ● Jumper wires Build the interface circuit: Refer to the schematic diagram (Figure 4.4) and recommended breadboard layout (Figure 4.5) as well as the VirtualBench setup (Figure 4.6). Figure 4.4.
Figure 4.5. UA741CN Connection Diagram Figure 4.6.
Exercise 4.1: Using the MSO and DC Power Supply 1. Enable Channel 1 and Channel 2 in the MSO section by clicking the square icon next to the channel names. Figure 4.7. MSO Probes Disabled (left) and Enabled (right) 2. Set DC power supply settings: a. +6 V rail: 2 V b. +25 V rail: 5 V c. -25 V rail: 0 V 3. Enable the DC power supply by clicking the DC power supply power button on the VirtualBench application. Figure 4.8. DC Power Supply Settings Enabled 4. Set FGEN settings: a. Frequency: 10 Hz b.
Figure 4.9. FGEN Settings Enabled 6. Scale the horizontal settings of the MSO display to accurately represent the frequency of the signal. For a 10 Hz stimulus signal, MSO horizontal settings set to 50 ms/, as shown in Figure 4.10, produce a clear and well-spaced waveform. Figure 4.10.
7. Observe the MSO readings, specifically the shape and range of the output signal. 8. Enable the cursors by clicking the cursor icon shown in Figure 4.11. The cursor menu provides the user with the option to select the measurement type and channel. Measure the maximum and minimum values of the output signal and record the voltage levels in the fields below. a. Square Wave Peak Voltage (V): _______________________ b. Square Wave Minimum Voltage (V): _______________________ Figure 4.11. MSO Cursor Menu 9.
Expected results: Channel 1 of your MSO should display the 10 Hz sine wave being fed to the V_in pin of the op-amp, while channel 2 should display a square wave resulting from the voltage level detector circuit (V_out). Whenever the sine wave, observed on channel 1 of the MSO, is below 2 V, then you should expect the signal observed on channel 2 of the MSO to be at 0 V. Alternatively, whenever the sine wave is above 2 V, then you should expect the signal observed on channel 2 of the MSO to be at 5 V.
Figure 4.14. Physical Circuit Test Results With Modified Supply Voltage 4.3 Interface Theory Without a feedback mechanism, the op-amp acts as a comparator. The inverting input (V_ref) serves as a reference voltage to compare the noninverting input to (V_in). If V_in is above V_ref, then the output (V_out) saturates to the op-amp’s positive power supply (+5 V). Otherwise, V_out saturates to the op-amp’s negative power supply (0 V).
