ECE 445, Exam 1 Review
ECE 445, Exam 1 Review ECE 445
Popular in Biomedical Instrumentation
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This 1 page Study Guide was uploaded by Rachel Streufert on Sunday October 2, 2016. The Study Guide belongs to ECE 445 at Michigan State University taught by Dr. Li in Fall 2016. Since its upload, it has received 22 views. For similar materials see Biomedical Instrumentation in Electrical Engineering at Michigan State University.
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Date Created: 10/02/16
Chapter 1: Basic Concepts Measurand Physical quantity, property or condition that carry information Typical biomedical measurand quantities Biopotential Pressure Flow Dimensions (imaging) Displacement (velocity, acceleration, and force) Impedance Temperature Chemical concentration Sensors Converts physical measurand to an electrical output Requirements Selectivity Should respond to a speciﬁc form of energy in the measurand Resolution Should respond to a small change of the measurand Minimally invasive Should not aﬀect the response of the living systems Signal Conditioning Ampliﬁcation, ﬁltering, and A/D and D/A conversion of the signal acquired from the sensor to make it suitable for display General categories Analog, digital or mixed-signal conditioning Time/frequency/spatial domain processing (e.g., ﬁltering) Calibration (adjustment of output to match parameter measured) Compensation (removal of undesirable secondary sensitivities) Operational Modes Direct vs. Indirect Direct Measures a physiologic parameter directly Example: Body temperature Indirect Measures a quantity that is accessible and related to the desired measurand Assume the relationship between the measurands is already known Often chosen when the measurand requires invasive procedure to measure directly Example: ECG recording measures the propagation of the action potential in the heart Sampling vs. Continuous Sampling For slow varying measurands that are sensed infrequently Examples: body temperature & ion concentrations Continuous For critical measurements requiring constant monitoring Examples: electro-cardiogram & respiratory gas ﬂow Generating vs. Modulating Generating AKA self-powered mode Derive their signal output from the measurand itself Examples: piezoelectric sensors & solar cells Modulating Measurand modulates the electrical signal which is supplied externally Modulation aﬀects output of the sensor Examples: photoconductive or piezoresistive sensor Analog vs. Digital Most sensors are inherently analog Require analog-to-digital converters before any DSP techniques could be applied for ﬁltering Real-time vs. Delayed-time Real-time Example: ECG signals need to be measured in real-time to determine an impending cardiac arrest Delayed-time Example: cell cultures which requires several days before any output is acquired Constraints of measurement Signal to be measured Measurement variability is inherent at molecular, organ and body level Caused primarily by interaction between diﬀerent physiological systems and existence of numerous feedback loops whose properties are poorly understood Signal/frequency ranges Most medical measurand parameters are typically much lower than conventional sensing parameters Microvolts, mmHg, low frequency Interference and cross-talk Noise from environment, instruments, etc. Other measurands aﬀect measurement (and can’t be isolated) Cannot measure EEG without interference from EMG Require ﬁltering and/or compensation Safety Due to interaction of sensor with living tissue, safety is a primary consideration in all phases of the design & testing process Damage caused could be irreversible In many cases, safe levels of energy is diﬃcult to establish Safety of medical personnel also must be considered Operator constraints Reliable, easy to operate, rugged and durable Classiﬁcations of biomedical instruments Quantity being sensed Pressure, ﬂow or temperature Makes comparison of diﬀerent technologies easy Principle of transduction Resistive, inductive, capacitive, ultrasonic or electrochemical Makes development of new applications easy Organ systems Cardiovascular, pulmonary, nervous, endocrine Isolates all important measurements for specialists who need to know about a speciﬁc area Clinical specialties Pediatrics, obstetrics, cardiology or radiology Easy for medical personnel interested in specialized equipment Regulation of medical devices FDA Regulation 3 classes More regulation for devices that pose greater risk Class I (General controls) Manufacturers are required to perform registration, pre-marketing notiﬁcation, record keeping, labeling, reporting of adverse experiences and good manufacturing practices Class II (Performance standards) 800 standards needed to be met Class III (Pre-marketing approval (PMA)) Requires extensive testing and expert scrutiny PMA is necessary for devices used in supporting or sustaining human life Implanted devices (pacemakers etc.) are typically designated class III Investigational devices are typically exempt Input Sources Desired Measurands that the instrument is designed to isolate Interfering Quantities that inadvertently aﬀect the instrument as a consequence of the principles used to acquire and process the desired inputs Generally not correlated to measurand Often easy to remove/cancel Modifying Undesired quantities that indirectly aﬀect the output by altering the performance of the instrument itself May be correlated to the measurand More diﬃcult to remove Compensation Techniques Negative feedback Used to make output less dependent own the transfer function of the device Used when modifying input cannot be avoided Open-loop and Closed-loop feedback Open-loop Seldom used for precise ampliﬁcation Large open-loop gain criterion Easy to satisfy Closed-loop Closed-loop gain can be set to almost any value Linearity and precision of closed loop amp Determined by ratio of resistors Easy to design ampliﬁers with high gain Precision not required Biostatistics Observational Studies Characteristics of one or more groups of patients are observed and recorded Data Analysis (Understand deﬁnitions/terminologies. Don’t need to memorize equations) Distributions Reﬂect the values of a variable/characteristic and frequency of occurrence of those values Mean Average of N values (arithmetic or geometric mean) Median Middle of ranked values Mode Most frequent value Standard deviation(s) Spread of data about the mean Coeﬃcient of Variation (CV) Permits comparison of measures on diﬀerent scales Percentile Percentage of distribution that is less than or equal to the percentile number Dynamic characteristics Zero-order Linear potentiometer is an example of a zero order instrument At high frequencies parasitic capacitance and inductance will cause distortion Step response is proportional to the input amplitude No variation with frequency First-order Instrument contains a single energy-storage element Step response is characterized by a single time constraint Chapter 2: Sensor Basic deﬁnitions and examples Transducer A device that converts a primary form of energy into a corresponding signal with a diﬀerent energy form Takes form of a sensor or an actuator Example: manometer Sensor A device that detects/converts a physical parameter to an electric signal Acquires information from the “real world” Example: thermometer Actuator A device that converts an electric signal to a physical output Example: heater Conventional sensors vs. Microelectronic sensors Conventional sensors Large, but generally reliable, based on older technology Examples: Thermocouple: temperature diﬀerence Magnetic compass: direction Microelectronic sensors Millimeter sized, highly sensitive, less robust Examples: Photodiode/phototransistor: photon energy (light) Infrared detectors, proximity/intrusion alarms Piezoresistive pressure sensor: air/ﬂuid pressure Micro accelerometers: vibration, change in velocity (car crash) Chemical sensors: O , CO , Cl, Nitrates (explosives) 2 2 DNA arrays: match DNA sequences Neural probes: detect brain signals Sensors for displacement measurement Resistive sensors (Potentiometers & Strain Gages) Inductive sensors Capacitive sensors Piezoelectric sensors Wheatstone Bridge Wheatstone bridge: Design and Analysis 5ACAD1ED-3CCC-40A1-9731-D25B154DEBB1.pdf 22.2 KB VCC - + Conﬁguration variable and ﬁxed elements used to monitor small variations in the elements (and optionally compensate for temperature eﬀects) 1 variable/sensor element bridge conﬁguration R 3s sensor element R set to match the value of R 4 3 If R1=R 2 Vout=0 V outvaries as R3changes
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