ELECTRICAL ENGINEERING

Introduction to Process Control Lab

1. You are taking a measurement of a signal from a sensor with high frequency noise. In order to not amplify that noise through your instrumentation system, you decide to use a RC filter with a cutoff frequency (critical frequency, fc) of 1kHz after the sensor and before the amplification.

a. What kind of RC filter do you need? Design the RC filter. Be sure to use standard resistor and capacitor values and specify the tolerance. Show all work.

b. Construct the circuit using Multisim. Use the tolerances which you specified in your design.

Use the multifunction generator for the input and use both channels of the Tektronix virtual scope to display the input and output voltages.

Create a table of your input and output voltage at dc, 250 Hz, 500Hz, 750Hz, 1kHz, 5kHz, 10kHz, 50kHz, 100kHz. Measure additional frequency points in order to get a nice set of data for the drop off. Be sure to capture several screenshots of the Tektronix virtual scope.

Given the output voltage at dc, what is the voltage 3dB down? In other words, what is the output voltage at the 3dB point? You should calculate this.

Using your simulation, change the frequency of the input voltage until the output voltage is that associated with your 3dB point. What is the frequency of the signal? That is your critical frequency. Take a screenshot of the scope. Add these measurements to your table. Also, put in your report this frequency. What is this frequency called?

Create a plot of your data (you can do this easily in Excel) and copy and paste the plot into your report.

Questions:

1. Does your circuit attenuate the signal at high frequencies? What is the attenuation at 10kHz?

2. How does your measured -3dB frequency (fc) compare to your design critical frequency? Give some reasons why it is different.

W2 Lab: Digital Signal Conditioning Lab

Instrumentation Measurement & Lab

Lab 2 hints For the 2 resistors on the left, they are in a voltage divider configuration. The directions say that you need 1.25V (out of that 5V dc). This 1.25V will be across the bottom resistor which by the way is typical in a voltage divider situation. This resistor value is what you will have to calculate (this is a design issue). I would recommend using in the kohms values. The far right resistor is just a pull-up resistor, typically kohms values as well. Adjust your design for it if you need to. The oscilloscope will show the effect of the variable input, the output being a square wave varying from 0V (when the input is above 1.25V) to 5V (when the input is below 1.25V). Other voltage readings using multimeters need to be taken as well of course. ps. Oscope – right-clicking on the triangles with the numbers at the top then selecting “Select a trace” will allow you to select which channel you wish to use (change which waveform you wish to follow)

Digital Signal Conditioning Lab

1. For the comparator below, complete the design so that the threshold voltage is 1.25V which means that if the input is below 1.25V, the output will be HIGH and if its greater, it will be low. Once the resistance values are found, use Multisim to validate the design by applying a sine wave of 3Vpp into Vin and plot the results.

figure 1

2. Using the 8 bit Digital-to-Analog (VDAC) in Multisim, design the part with a 12V reference. Next apply the following inputs in the table below and both calculate and measure the output voltage. What is the resolution of the DAC? Show your circuit and results in Multisim.

Digital Inputs Calculated Analog Output Voltage Measured Analog Output Voltage
7 6 5 4 3 2 1 0
0 0 0 0 0 0 0 1    
0 0 0 0 1 0 0 1    
0 0 0 1 0 0 0 0    
0 0 0 1 1 1 1 1    
0 1 0 1 0 1 0 1    
1 0 0 0 0 0 0 0    
1 1 1 1 1 1 1 1    

W3 Lab: Thermal Sensors Lab

Instrumentation Measurement & Lab

Thermal Sensors Lab

1. In a processing plant, a chemical tower has a liquid which is vaporized. However, if the vapor in the tower reaches 150°C, an alarm needs to be generated so that safe shutdown of that system of the plant may be initiated. An RTD will be used to measure the temperature of the vapor. The RTD will generally operate between 80° to 175°C and has a resistance of 220Ω at 20°C. The fractional change in resistance per 1°C is 0.0040. The dissipation constant is 25mW/°C. Design a circuit to activate an LED alarm when the temperature reaches 150 °C. The error should not exceed +/-1°C. Use a single supply voltage.

a. Draw a block diagram for your design. Explain the function of each block and why it is needed.

b. Design the circuit showing all calculations. Choose standard resistor values, and specify the tolerances. Provide a drawing of your circuit with all resistor values and tolerances and parts. You may do this by creating it in Multisim and then drawing the values on as appropriate.

c. Construct the circuit in Multisim using the resistor values you chose and tolerances. Do a screenshot showing how you have set up the tolerances for the resistors. For the RTD, you may use a potentiometer or variable resistor for which you can change the resistance for different temperatures. If you have a bridge circuit with a potentiometer for nulling, explain how you decide what resistance to use for the null.

d. Create a table of temperature, RTD resistance, RTD resistance adjusted for self-heating, LED Status. Test your circuit, and use the table to display your results. Find the precise resistance and temperature at which the LED turns on. Provide several screenshots showing the resistance which reflects the RTD resistance value used in the circuit and the LED alarm. Which RTD resistance do you use in the circuit for testing?

e. Put together all of the above in a well-written report including introduction, requirements, block diagram, design calculations, final design (including any potentiometer settings), testing (including which RTD resistance is used in the circuit for testing), and analysis of results. Be sure to provide a summary at the end, noting at which temperature the alarm was activated, if this was as designed, and what accounts for differences. Please note any problems you encountered.

f. Entitle your report as EE372W3LYourGID.docx (or other word processing document). Save your Multisim file as EE372W3LYourGID.ms. Submit both documents.

W4 Mechanical Sensors Lab

Instrumentation Measurement & Lab

Mechanical Sensors Lab

1. A capacitive displacement sensor is used to measure rotating shaft wobble shown in the figure below.  The capacity is 520 pF with no wobble.  Find the change in capacity for a +0.035 to -0.035 mm shaft wobble.  Show your calculations.

figure 1

2. To measure the displacement, assume that the capacitive pickoff in problem 1 is used in an AC bridge constructed of only capacitors.  Using 520pF for the bridge capacitors, find the offset bridge voltage for the two extremes of shaft wobble.   Assume a sine wave voltage input having an amplitude of 5 Vrms and a frequency of 5 kHz.  Rather than using an equation from the book, you are required to derive the offset bridge voltage using circuit analysis principles.  Show all your calculations.

3. Using Multisim, construct and simulate the AC bridge of problem 2 for the two extreme conditions.  Be sure to provide screenshots.  Also, write a brief summary, noting if the results matched expected results.

W5 Lab: Optical Sensors Lab

Instrumentation Measurement & Lab

Optical Sensors Lab

1. Using Multisim, design a system using the photoconductive cell shown in the figure below to measure and display light intensity. Make the design such that 20 to 100mW/cm2 produces an output of 0.2 to 1.0V. What is the readout error when the intensity is 60mW/cm2? Show all calculations and Multisim results.

figure 1

2. For the turbidity system show in Figure 2 below, two matched photoconductive cells are used in R vs. IL as given in Figure 3 below. Design a signal-conditioning system that outputs the deviation of the flowing system turbidity in volts and triggers an alarm if the intensity is reduced by 10% from the nominal of 15mW/cm2.

figure 2

Figure 2

figure 3

W6 Lab Final Control Lab

Instrumentation Measurement & Lab

Final Control Lab

1. The SCR in Figure 1 below requires a 3 V trigger.  Using Multsim, design a system by which the gears are shifted when a CdS photocell resistance drops below 4kohms.

figure 1

Figure 1

2. Using Multisim, design a system by which a control signal of 4 to 20 mA is converted into a force of 200 to 1000N.  Use a pneumatic actuator and specify the required diaphragm area if the pressure output is to be in the range of 20 to 100kPa.  An I/P converter is available that converts 0 to 5 V into 20 to 100 kPa.  A block diagraph of the system is shown below.  (Hint:  Use a differential amplifier.  You are only designing the circuit to interface into the I/P below)

figure 2

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