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MECH2460 3660 8660 9660 Manufacturing Engineering Assignment 1 Part B (12.5%) Due Friday 11:59pm 24th of March (Week 5) Data Acquisition and LabVIEW – Pulse Oximetry Case Study Background: A pulse oximeter is a non-invasive medical device used to measure the percentage oxygen saturation in the blood. Oxygen saturation should always be above 95%, although in those with long-standing respiratory disease or cyanotic congenital heart disease, it may be lower, corresponding to disease severity. The pulse Oximeter operates by shining light at two different wavelengths through part of the patient’s body where blood is present such as a finger or earlobe, and monitoring the change in light absorption due to the blood pulsing. In general, haemoglobin can be saturated with oxygen molecules (oxyhaemoglobin), or lacking oxygen molecules (deoxyhaemoglobin). The absorption spectra of oxyhaemoglobin and deoxyhaemoglobin differ. The oxyhaemoglobin has significantly lower absorption of red light than deoxyhaemoglobin, while for infrared light its absorption is slightly higher. This difference accounts for the presentation of cyanosis, the blue to purplish colour that tissues develop during hypoxia (when the body is deprived of oxygen).This difference is also used for measurement of the amount of oxygen in patient's blood by the pulse oximeter. The raw signal received from the pulse oximeter transducer at each wavelength has the AC pulse component we are interested in on top of a large offset, as the absorbance change caused by the blood pulse is small compared to the absorption of the rest of the tissue the light must pass through. It is the ratio of the AC pulse peak values measured between the two wavelengths that is used to calculate the percentage of oxygen saturation in the blood. http://en.wikipedia.org/wiki/Absorption_spectrum http://en.wikipedia.org/wiki/Cyanosis http://en.wikipedia.org/wiki/Hypoxia_(medical) http://en.wikipedia.org/wiki/Pulse_oximeter The pulse oximeter uses very complicated calculations to work out oxygen saturation that depend on the exact light wavelengths used by the device. The formulas and outputs are also calibrated using historical databases of known blood oxygenation levels compared with actual peak ratios measured from the device. To keep things simple for the purposes of this assignment, let us assume that the ratio of the red and infrared absorption peaks can be converted to percentage oxygen saturation using the simple linear relationship below, which approximates the actual conversion formulas: Oxygen Saturation (%) = -34 X R + 117 Where R = Red Peak / IR Peak Part a: System Design (3.5 Marks) Many things must be considered when choosing appropriate data acquisition hardware for use in a product, including but not limited to sample rate, resolution, channel numbers, and cost. 1. With this in mind, give the minimum frequency (in Hz) needed to measure the pulse oximeter signal. Assume human heart rates can range from 32 beats per minute to 220 beats per minute. To measure peak values, you will need to sample fast enough to obtain a good pulse shape, and in the case of this application we would like to see at least 100 points representing each signal period (entire pulse). 2. Assuming you want a minimum of 3 pulses for calculations how long will you need to capture the signal for on the DAQ device? 3. Calculate the minimum resolution (in bits) needed to measure the pulse oximeter signal. Assume that you need to resolve a change of 0.001V in the signal and the DAQ device has a range of ±10V. 4. Which of the following National Instruments DAQ cards would be the best choice for this application (note: you will have to look up the specifications for these DAQ cards on ni.com). Please provide reasoning. a. NI USB-6000 b. NI USB-6002 c. NI USB-6525 d. NI USB-6351 5. The pulse oximeter sensor outputs a 0-15V signal typically with high frequency noise up to 150Hz. Discuss the signal conditioning we should consider? 6. Provide a diagram of the Data Acquisition system, from the PC to the sensor, including required software components. Part b: Analysing the Acquired Data using LabVIEW (9 Marks) Using the signals in the file “Pulse Oximetry Raw Data.lvm”, use LabVIEW to determine: a. The oxygen saturation of the patient (%) b. Check that the oxygen saturation is within a healthy range of 95% to 100% (inclusive) c. The heart rate of the patient (Beats Per Minute) d. Check that the heart rate is within a healthy range of 50 BPM to 90 BPM (inclusive) e. Write the results to a .csv file, including header information, that opens in both Notepad or other text editor and Excel as shown below: Figure 1: CSV File output example shown in Notepad and Excel Development Guide: a. Start by loading the “Pulse Oximetry Raw Data.lvm” data into a new LabVIEW VI by using a “Read From Measurement File” Express VI. b. Plot the raw Red and Infra-Red (IR) waveforms on a graph. You will notice that the interesting part of the waveforms is offset, as the absorbance change caused by the blood pulse is small compared to the absorption of the rest of the tissue the light must pass through. c. Find the DC offset and remove it from the raw data. d. Remove measurement noise and plot the processed waveforms on a graph. e. Use Express VIs and basic array and numeric functions to determine and display the oxygen saturation and heart rate of the patient. f. Use LabVIEW functions to check that the oxygen saturation and heart rate of the patient are within their healthy ranges and display a clearly visible warning if they are not. g. Write your results to a .csv file that can open in Excel. Submission instructions You will need to submit two documents, your LabVIEW VI for Part b and a Word or .PDF document explaining your answers to Part a. When you have completed your written answers and LabVIEW program, include your SID in each filename as per the example below, compress in a zip file as described below, and upload your files through Canvas. 310275433.docx 310275433.vi Compress to single file for upload: 310275433.zip If these rules are not adhered to, your assignment will not be marked! Part a: (3.5 Marks) Submit your answers, calculations, and reasoning as a Word or .PDF Document. Part b: (9 Marks) Submit your LabVIEW file(s). The following calculated values should be clearly displayed on the user interface upon running the program. • Oxygen Saturation (%) • Heart Rate (BPM) As well as receiving marks for the correct file reading setup and calculation results, your LabVIEW code will be used to analyse your methodology and understanding of the software package. Your code will be used to provide partial marks where relevant. Consider the following: • Logical function/vi selection and ordering • Meaningful labels on graphs and indicators • Intuitive Front Panel design • Ease of use (consider file paths) • Block Diagram Comments • Neat, readable code that is not overly complicated