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BME Instrumentation

Instrumentation Exam 1

What is a transducer? A device that converts a form of energy into another. such as pressure or brightness, or vice versa
What is instrument Zero drift? drifts at the x=0, slope is the same, everything just shifts up and down.
Gain Drift? The maximum variation of gain as a function of time, with all other parameters held constant. (aka sensitivity drift)
Saturation? The state or process that occurs when no more of something can be absorbed, combined with, or added in order to limit operating range.
What is a Peltier heat pump? A solid-state active heat pump which transfers heat from one side of the device to the other side against the temperature gradient (from cold to hot), with consumption of electrical energy
What controls the direction of heat flow? (Peltier heat Pump) The current controls the direction of heat flow.
Under what circumstances would an LVDT be preferable to a strain gauge? When the displacement is a great distance rather than a small one which is used with strain gauges
Why is it that cancer tumors show up on thermograms? They show up on thermograms because of the increased blood supply activity (warmer) around the tissue in order for the tumor to grow and obtain nutrients.
If the region over the tumor is 0.5 C warmer than the surrounding, what is the increase in its radiant energy? An increase of .5 C yields an increase of radiant energy by a factor of 0.0675?? This depends on the temperature of the surroundings, probably body temperature (310 K). Wt = J = sigma * epsilon * T^4
What is the difference between a photoplethysmograph and a photo-oximeter in terms of their function? ● Photoplethysmograph: measures pulse by volume change--Photo(light)plethysmo(volume change)graph(output) (note: used in pulse oximeters) ● Photooximetry: measures blood O2 saturation (%)
What is an isosbestic point in photo-oximetery? Isobestic point--point where fully oxygenated blood and deoxygenated blood show the same relative absorbance (also falls about the infrared wavelength ~805 nm in our textbook)
What is an isosbestic point in photo-oximetery used for? ●This works as a great calibration point so that color of skin and thickness of measured area are irrelevant
What is the advantage of EM flow measurements over thermodilution for cardiac measurements? The electromagnetic flowmeter measures instantaneous pulsatile flow of blood and thus has greater capability than indicator-dilution methods which measure only average flow. It operates with any conductive liquid, such as saline or blood
What are the disadvantages of thermodilution method? 1)-maybe an inadequate mixing between the injection site and sampling site. 2)-maybe an exchange of heat between the blood and the walls of the heart chamber. 3)maybe heat exchange through b the catheter walls before,during and after injection.
Explain how thermodilution works for cardiac output? Cold saline is injected through a catheter into the pulmonary artery.The indicator is mixed with blood in the right ventricle. There is a thermistor located near the catheter tip, the temp change is measured.
thermodilution works for cardiac output. Does the recorded temperature rise or fall with increased flow? From equation 8.7, flow (F) and temp (T) are inversely proportional. See book page 343.
What is the piezoresistive effect? uses mechanical stress to change resistivity R=p*l/A, where p=resistivity. the resistivity is directly proportional to resistance and indirectly proportional to surface area.
how does the piezoresistive affect performance of metal film strain gauges? In metal film strain gages, the gage is stretched and resistance changes, but only for small displacements.
how does the piezoresistive affect performance of semiconductor gauges? Gage Factor: (deltaR/R)/(deltaL/L) measures sensitivity of resistive element to strain. Important in semiconductor strain gauges when you use silicon, where del rho / rho is very large
Overall how does the piezoresistive affect performance of gauges? Negligible for metal film strain gauges, dominant for silicon strain gauges.
How do semiconductor strain gages cope with the temperature dependence of the semiconductive gauge elements? Temperature change produces an error in strain gauges. This is dealt with by adding another gauge, or having 4 gauges. In this way, there overall change can be subtracted which will eliminate the error. (wheatstone bridge)
What is the usefulness of a bridge circuit connection of transducers? ●Temperature coefficient of gauges cancel (over some range) ●Bridge output is 2 times higher ●Strictly linear output regardless of non-linearity in the gauge
What is mutual inductance? Mutual inductance is when there are 2 inductors and the magnetic field of the primary inductor induces a magnetic field in the secondary inductor, putting each other at resonance i.e. both share the same frequency and magnetic field.
What is piezoelectricity? Piezoelectricity is the charge which accumulates in certain solid materials (notably crystals, certain ceramics, and biological matter such as bone, DNA and various proteins)[1] in response to applied mechanical stress
What is the time constant of a PZT (piezoelectricity) transducer? time constant = RC, which is the discharge time for the circuit.
What are PZT (piezoelectricity) transducers used for? PZT measuring systems can’t do static measurements (like weight) because they only produce charge output with a *change* in load.
Why can't a PZT crystal measure weight? What is it about the electrical nature of the crystal that causes this? Not all piezoelectric materials can be poled (?)
What is a frequency response (Bode) plot? A Bode plot is a graph of the transfer function of a linear, time-invariant system versus frequency, plotted with a log-frequency axis, to show the system's frequency response.
What is its typical shape for a piezoelectric force transducer response? What does this mean? The typical shape for a PZT plot is a high pass region, followed by a flat region, then a sharp peak where resonance takes place. The flat region is the useful region.
If a blood transducer diaphragm has a higher Young’s modulus, what is the overall effect on the electrical output from the internal strain gages as a function of pressure? If the Young’s modulus increases (stress/strain) the stress at the center will decrease, meaning lower electrical output (see equation from notes)
What is the Seebeck effect? ●Passing current through thermocouple, heats one junction and cools other (reversible by switching current flow) ●Poor efficiency ●Useful for spot cooling
What is the peltier effect? ●Voltage generated by dissimilar metals (or semiconductors or some cases even liquids--but book says metals) subject to a change in temperature
What electrical effect results from heating a thermocouple wire pair in the middle of its length? Intermediate temperatures do not have an effect. Nothing will happen.
Are EM flowmeters sensitive to the direction of blood flow? How? Yes, the flowing blood moves through a magnetic field inducing a measureable emf in the electrodes used by the EM flowmeter. The direction of the blood can then be found by the right hand rule.
What are the various phases of the Korotkoff sounds? 1. Silence 2. Phase I: snapping tone --> Systolic Pressure (apparent systolic pressure ~5mmHg low compared to true) 3. Phase II: murmurs 4. Phase III: thumping 5. Phase IV: muffling 6. Silence
How is systolic pressure determined from them? Systolic pressure is coincident w/ phase I sound -- think about it, the vessel experiences the same pressure as the cuff pressure, and as soon as it opens the vessel, you get your snap sound and this is your systolic pressure
To measure an EMF across a blood vessel, in which direction must be the magnetic field for maximum potential? Perpendicular to the direction of flow, by right hand rule?
Created by: Mabel_Munoz