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# Signal processing and filters for reg review ms ni

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Everything you need to know about the technical aspect of data collection

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• Slide 29 is incorrect V = 7 microvolts/mm X 12 mm as the example asks, not 11. So the answer should be 7x12= 84 microvolt

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### Signal processing and filters for reg review ms ni

1. 1. Amplifier Function and Signal Filtering usedin Sleep Disorders Technology An Overview
2. 2. Amplifiers and Signal FilteringYou Need to know: What differential amplifier is What CMR is and how it works How TC filters work and TC relationship to LFF How LFF and HFFs work to reduce unwanted frequencies How a 60Hz notch filter works Know basic polarity problems The difference between an AC and DC amplifier The difference between gain and sensitivity 2 Midwest Sleep and Neurodiagnostic Institute, Inc
3. 3. Terms for Basic Electricity Impedance: The total opposition to current flow including resistance, inductance and capacitance. Measured in ohms. Resistance:The opposition to the flow of current. Measured in ohms. Volt: Measurement of the force pushing current (electrons) through a conductor. Polarity: Refers to the positive or negative poles of a device 3 Midwest Sleep and Neurodiagnostic Institute, Inc
4. 4. Alternating Current (AC) Alternatively flows between positive and negative (protons+ and electrons-) Alternates at 1/60 sec in USA  1/50 sec in Europe 4 Midwest Sleep and Neurodiagnostic Institute, Inc
5. 5. Ohms Law Voltage is equal to current flowing in the circuit, multiplied by the resistance. Voltage = E (volts) Current = I (amps) Resistance = R (ohms) 5 Midwest Sleep and Neurodiagnostic Institute, Inc
6. 6. V= I x R E Voltage Current Resistance I I R RR E I E 6 Midwest Sleep and Neurodiagnostic Institute, Inc
7. 7. The Polygraphic Circuit The function of the polygraph is to transform voltages generated by body into an interpretable record 7 Midwest Sleep and Neurodiagnostic Institute, Inc
8. 8. G2 G1 - - - - + + +ChartDrive - - + ++ Paper / computer 8 Midwest Sleep and Neurodiagnostic Institute, Inc
9. 9. Signal Processing Electro conductive material Electrode  These act as a small capacitor Wire to head box Exploring electrode  C3, C4  O1, O2 Reference electrode  A1, A2 9 Midwest Sleep and Neurodiagnostic Institute, Inc
10. 10. 10Midwest Sleep and Neurodiagnostic Institute, Inc
11. 11. GroundLeakage current results when there iseither a break or a shunt in the circuit.Patient grounding is essential in artifactelimination and proper amplifier function. Symbol for Ground 11 Midwest Sleep and Neurodiagnostic Institute, Inc
12. 12. Differential Amplifier Form of AC amplifier Amplifies the difference between input (grid) 1 and input (grid) 2 Rejects any similar information between G1 and G2 (CMR) 12 Midwest Sleep and Neurodiagnostic Institute, Inc
13. 13. Common Mode RejectionCommon function of differential amplifierRejection of similar activity between input1 and input 2  Identical information rejected at near 100% 13 Midwest Sleep and Neurodiagnostic Institute, Inc
14. 14. Polarity and Localization Input 1  When input one is negative, the pen goes up, when input one is positive, the pen goes down. Input 2  When input two is positive, the pen goes up, when input two is negative, the pen goes down. 14 Midwest Sleep and Neurodiagnostic Institute, Inc
15. 15. Basic Polarity and Localization Up rules Down rulesInput 1 (G1) Negative Positive Input 1 rulesInput 2 (G2) Positive Negative Input 2 rules 15 Midwest Sleep and Neurodiagnostic Institute, Inc
16. 16. AC coupled AmplifierCommon Mode Rejection Ratio Common Input Signal Should be high ie. 100,000 to 1 Output Signal 16 Midwest Sleep and Neurodiagnostic Institute, Inc
17. 17. Polarity Calculation 26 uv + 41 uv -15 uv 26 - 15 + 41 uv 17 Midwest Sleep and Neurodiagnostic Institute, Inc
18. 18. Galvanometer Limited to a maximum response of 90 - 120hz 18 Midwest Sleep and Neurodiagnostic Institute, Inc
19. 19. Amplifier/Machine CalibrationAll filters set the same 19 Midwest Sleep and Neurodiagnostic Institute, Inc
20. 20. Montage Calibration 20 Midwest Sleep and Neurodiagnostic Institute, Inc
21. 21. Time Axis The point (time) at which each pen falls along the same recording line The galvonometer or pen mount may be adjusted to correct problems Not a problem with digital systems 21 Midwest Sleep and Neurodiagnostic Institute, Inc
22. 22. Damping Adjustment to reduce overshoot good Reduces erroneous fast-wave artifact Only adjusted on Under polygraphs damping  Not digital systems Over damping 22 Midwest Sleep and Neurodiagnostic Institute, Inc
23. 23. Mechanical BaselinePen spacing without amplifier input to pens. 23 Midwest Sleep and Neurodiagnostic Institute, Inc
24. 24. Electrical Baseline The “electrical zero” of a recording pen position Mechanical Baseline needs Found by turning the adjustment individual chart amplifier power off and on while adjusting the baseline knob. EZ if found when the pen stops changing Electrical Zero positions between power-on, and power-off 24 Midwest Sleep and Neurodiagnostic Institute, Inc
25. 25. 1. Unequal sensitivity 2. Pen alignment— time axis 3. Pen baseline off 4. LFF different setting 25 Midwest Sleep and Neurodiagnostic Institute, Inc
26. 26. Gain vs. Sensitivity Gain is a measure of the ability to change the magnitude of the input voltage Sensitivity is the amount of output (pen deflection) to a given input voltage 26 Midwest Sleep and Neurodiagnostic Institute, Inc
27. 27. V= S x PD V uV Voltage Sensitivity Pen Deflection S S PD uV/mm mm PDPD V S V 27 Midwest Sleep and Neurodiagnostic Institute, Inc
28. 28. Sensitivity CalculationsSensitivity is at 5uv/mm the voltage is 50 uv what is the deflection? D = V/S D = 5uv/mm 50uv D = 10 mm 28 Midwest Sleep and Neurodiagnostic Institute, Inc
29. 29. Sensitivity is set at 7 uv/mm and thedeflection is 12 mm. What is thevoltage?V=SXDV = 7uv/mm X 11 mmV = 77 uv 29 Midwest Sleep and Neurodiagnostic Institute, Inc
30. 30. Voltage is 75uv and the deflection is 15 mm. What is the Sensitivity setting?S = V/DS = 15mm 75 uvS = 5 uv/mm 30 Midwest Sleep and Neurodiagnostic Institute, Inc
31. 31. 60 Hertz Notch Filter Also known as an AC Filter In North America, all AC electrical current oscillates at 60 Hz. Uses CMR by tapping into line current and measuring it against output. 31 Midwest Sleep and Neurodiagnostic Institute, Inc
32. 32. 60 Hertz Notch Filter100 90 80 70 60 50 40 30 20 10 0 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 32 Midwest Sleep and Neurodiagnostic Institute, Inc
33. 33. Units of Measure Used in Filtering Hertz (Hz)  Most common unit in electroneurodiagnostics Second (sec)  Used in Time Constant (TC) filter calculations Decibels (dbl)  Most basic unit of measure in frequency filtering  Rarely referred to in sleep diagnostics 33 Midwest Sleep and Neurodiagnostic Institute, Inc
34. 34. Time Constant (TC)Units = seconds (s)The time it takes in seconds 100% for a waveform to drop to 37% of its calculated amplitude 37%Faster TC – Reduces .003 .3 1amp. of slow frequencies Time (s)Low cut – high pass filter 34 Midwest Sleep and Neurodiagnostic Institute, Inc
35. 35. TC (sec) and LFF (Hz) Relationship TC and LFF work with same goal  Reduction of slow frequencies  Different units of measure to describe the same action Conversions: 1 1LFF = TC = 2π x TC 2π x LFF 35 Midwest Sleep and Neurodiagnostic Institute, Inc
36. 36. Basics of LFF and HFFs Reduces amplitude of listed frequency at a fixed value  20% (Nihon Kohden)  30% (Grass) Reduces amplitude of frequencies above (HFF), or below (LFF) at linear levels 36 Midwest Sleep and Neurodiagnostic Institute, Inc
37. 37. Low Frequency Filters Designed to reduce the amplitude of frequencies at and below the selected frequency “Low cut, high pass filters”. 37 Midwest Sleep and Neurodiagnostic Institute, Inc
38. 38. Expected Amplitude Decay: LFF = 10Hz Based on Nihon Kohden filters 100 90 Reduces amplitude of a 10 Hz signal by 20% 80  Reduces a 5 Hz signal by 50%Amplitude 70 60  Reduces a 2.5Hz signal by 75% 50  Reduces a 1.25 Hz signal by 87.5% 40 30 20 10 0 1.25Hz 2.5Hz 5Hz 10Hz 38 Midwest Sleep and Neurodiagnostic Institute, Inc
39. 39. 39Midwest Sleep and Neurodiagnostic Institute, Inc
40. 40. Low Frequency Response Curve 40 Midwest Sleep and Neurodiagnostic Institute, Inc
41. 41. High Frequency Filters Designed to reduce the amplitude of frequencies at and above the selected frequency High cut – low pass filters 41 Midwest Sleep and Neurodiagnostic Institute, Inc
42. 42. Expected Amplitude Decay: HFF = 70Hz (based on Nihon Kohden filters) 100 90 Reduces amplitude of a 70Hz signal by 20% 80 Reduces a 140 Hz signal by 50%Amplitude  70 60  Reduces a 280 Hz signal by 75% 50  Reduces a 560 Hz signal by 87.5% 40 30 20 10 0 70Hz 140Hz 280Hz 560Hz 42 Midwest Sleep and Neurodiagnostic Institute, Inc
43. 43. High Frequency Response Curve 43 Midwest Sleep and Neurodiagnostic Institute, Inc
44. 44. 44Midwest Sleep and Neurodiagnostic Institute, Inc
45. 45. Filters Effect Amplitude & PhaseHigh FilterLow Filter Note: The Higher the filter the lower the amplitude Digital Filters will not cause a Phase Shift 45 Midwest Sleep and Neurodiagnostic Institute, Inc
46. 46. Direct Current Amplifiers Used to amplify signals which represent either all negative, or all positive voltage  Not alternating between – and + (AC) Used most often with slow trending data (SaO2 and heart rate trending) No LFF or HFF filters utilized  TC infinite (No frequencies to filter) 46 Midwest Sleep and Neurodiagnostic Institute, Inc
47. 47. Wheatstone Bridge Circuit A four-arm bridge used to measure resistance in a circuit Commonly used in DC amplifiers when resistance devices are in use  Strain gauges  NPT  Effort gauges 47 Midwest Sleep and Neurodiagnostic Institute, Inc
48. 48. Analog to Digital Conversion Brainwaves and other PSG signals are analog or continuous Digital is based on values of 0 or 1 ADC samples the signal and assigns a digital value 48 Midwest Sleep and Neurodiagnostic Institute, Inc
49. 49. Sampling Rate The rate at which the computer program samples the analog information to convert it to digital signal.  The faster the sampling rate the more accurate the tracing is  The faster the sampling rate the larger the patient data file will be 49 Midwest Sleep and Neurodiagnostic Institute, Inc
50. 50. Sampling Rate Nyquist principle  The sampling rate must be at least twice as fast as the fastest frequency that will be recorded.  ASET Standard is three times faster than the HFF setting  Can vary by channel  200+/sec for EEG  10/sec for respiratory 50 Midwest Sleep and Neurodiagnostic Institute, Inc
51. 51. Sampling Rate Aliasing  Sampling rate too low 51 Midwest Sleep and Neurodiagnostic Institute, Inc