Instrumentation Measurement and Lab

Discussion

Choose a control system that has direct impact on your daily life. Explain how this control system affects your life. Is it analog, digital or both? Identify the main elements in the control system. For instance, what is the sensor, what is the actuator, what is the controlled variable, etc? Are there any safeties or environmental considerations in the operation of the control system?

Assignment

Introduction to Process Control

Work the problems below. To receive any credit, you must show all work. You may submit your work in a word processing document or in a pdf file. Graphic files are not acceptable submissions. Your file submission document should be entitled Week1AYourGID (replace YourGID with your specific GID).

1. A sensor has a linear resistance change of 100 to 195 ohms, as temperature changes from 20^o- 120^oC. Find the I/O relationship.

2. Using the equation for modeling a 1^st order response, find the time it takes for a sensor to reach 90% of it final value given a final sensor output of 4.0V, an initial sensor output of 2.0V, and a time constant = 0.0025/s.

3. A 1000 ohm resistor is measured 10 times and the following readings were taken in the table below.

a. Find the mean and standard deviation of the measurements.

b. Assuming a normal distribution, there is a 99.7% probability that the true value of the resistance falls between what two values?

4. The following unbalanced Wheatstone Bridge is constructed. Calculate the output voltage across points C and D and the value of resistor R₄ required to balance the bridge circuit.

5. Refer to the op amp below (Fig. 2.26 in your text). If V_in = 0.5V, R₁ = 10k ohm, and R₂ = 25k ohm, calculate:

a. the output voltage, V_out,

b. the current in the 10k ohm resistor.

c. What would be the use or purpose of such a circuit? And how do your results demonstrate that?

Introduction to Process Control Week 1 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, f_c) 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 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 10 kHz?

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