Homework #2ME 368 - Engineering Measurements and Instrumentation
Duein .pdf format, submitted in ecow2, prior to your lab, Sept 21 or 22, 2009Fall Semester 2009
HW Problem 2-1:
(Objective: understand stationarity, ergodicity)
Consider each of the 3 ensembles available at
for each answer:
a)Are the ensembles stationary? (explain your reasoning)
b)Are the ensembles ergodic? (explain your reasoning)
HW Problem 2-2:
(Objective: Understand digitization and quantization error)
- Read Chapter 3 of the King textbook and section 6.7 of the Dunn textbook.
- Find the specifications and/or manual for the National Instruments 9215 data acquisition module
a)Describe in your own words what quantization error is
b)Describe in your own words what digitization resolution is
c)What is the digitization resolution of the 9215 analog input module?
d)What is the absolute quantization error of the 9215 analog input module?
e)Briefly explain in your own words why the two are different.
HW Problem 2-3:
(Objective: Understand Digital Sampling)
- Read section 12.3 in the Dunn text book
a)If you sample a signal at 1000 Hz using 100 samples, what will the minimum resolvable frequency be?
b)If you wish to sample a signal that has a frequency of 542 Hz and you wish to know this frequency to within 0.5 Hz, what is the minimum sample rate you need to use and how many samples are required?
c)Define aliasing in your own words
d)Explain why you should generally sample a signal at several times the required minimum sample rate (i.e., you should use a sampling frequency much higher than the minimum sampling frequency that will allow you to measure the maximum frequency contained in your signal).
Prelab Project
Create a temperature measurement VI by following the steps in Chapter 4 of the King textbook. I.e., build the VI step-by-step as you read through the chapter.
You will not have a temperature measurement device, so you will not be able to use the DAQ Assistant to read a temperature. You can simulate a T-Type thermocouple with somewhat realistic output using this Simulate Signal configuration:
This source will generate a signal that looks like a real thermocouple output that has been corrected using an ice-bath reference. To convert this to degrees Celsius, you must use this polynomial:
where
c1 = 2.592800×101
c2 = -7.602961×10-1
c3 = 4.637791×10-2
c4= -2.165394×10-3
c5 = 6.048144×10-5
c6 = -7.293422×10-7
So, in place of the DAQ Assistant used in the Chapter 4 example, you will use the Simulate Signal Express VI shown above together with a Formula Express VI to generate a signal that is in degrees Celsius. You will implement the case structure as described in the chapter to convert your display between Celsius and Fahrenheit.
To turn in:
1)Generate a description of your VI after completing the first conversion (i.e., through the section ending on the top of page 77). Do this by
- Going to the Print menu and printing the current setup (i.e., just click “Next” at the bottom of the first dialog box)
- In the next dialog box, select “Icon, description, panel and diagram” and click “Next”
- Select Rich Text Format in the next dialog box and click “Next”
- Write a file name and click “Save”
- You now have a file that will open in almost any word processor that completely documents your VI. You will be able to cut and paste from this file into your report.
This will generate a file that you can open in Microsoft Word or any other word processing document.
2)Generate a description of your VI after completing the Case structure (i.e., completing the steps described through the section ending on Page 83).
3)Generate a description of your VI after adding the While loop (i.e., completing the steps described through the section ending on Page 87).
4)Generate a description of your VI that uses Software Control Timing
Combine these four files with your homework responses and generate one PDF file. This can be done by combining everything in a word processing document, or by generating individual PDF files and combining the PDF files.