Gas station without pumps

2012 August 19

Medical Instrumentation, Chapters 9–14

As I mentioned in Medical Instrumentation, first 5 chapters, Medical Instrumentation, Chapter 6,  and Medical Instrumentation, Chapters 7 and 8, I’ve been slogging through one of the potential text books for the circuits course: Medical Instrumentation: Application and Design, 4th Edition. John G. Webster. Publisher: Wiley, 2009. # ISBN-10: 0471676004; # ISBN-13: 978-0471676003.  Here are my notes on the rest of the book (I plan to return it tomorrow to the library).

Chapter 9

Frank P. Primiano, Jr.

I only skimmed chapter 9, as there did not seem to be much of use for the circuits course.

Richard had suggested making a rotating-vane flowmeter using a toy siren-whistle as the turbine and a photodetector to determine its speed.  I investigated that possibility, but the siren whistles have very low drag on their turbines and continue to spin for a couple of seconds after the air flow has stopped.  One might be able to use that for a wind-speed indicator, but the response time is far too slow for measuring air flow due to breathing.

The section on measuring gas concentrations is intellectually interesting and may be of some value to bioengineers, but doesn’t seem relevant for the circuits course.

Chapter 10

Robert A. Peura

It’s nice to know how a pH probe works and how blood gases are measured, but I don’t see a lot we can do in the circuits class.
The plot of the absorptivities of carboxyhemoglobin, oxyhemoglobin, reduced hemoglobin, and methmoglobin in Figure 10.6 are interesting, and are needed for explaining how a pulse oximeter works, as well as why 940nm LEDs should be a good choice for detecting arterial blood pulses, since reduced hemoglobin has about 3/5th the extinction coefficient of oxyhemoglobin there.  An even longer wavelength (say 1000nm) would be even better, since the ratio drops to about 1/4, if LEDs and phototransistors for that wavelength were readily available, but 950nm is about as long a wavelength LED as is available.

I considered doing a pulse-oximetry lab, but the difficulty of calibrating the device made it seem pointless.  That’s too bad in a way, as the technique relies inherently on considering the AC rather than the DC component of the signal.

Chapter 11

Lawrence A. Wheeler

Nothing in this chapter seems relevant to the circuits class.  I had at one point considered doing a very early lab in which electric fields were illustrated by measuring voltages at different points in an electrophoresis gel, but that didn’t seem worth the messy setup.  Most of the bioengineers will do gel electrophoresis in other labs anyway.

Chapter 12

Melvin P. Siedband

Nothing in the imaging chapter seems relevant for the circuits class.

Chapter 13

Michael R. Neuman

It doesn’t look like there is anything in Chapter 13 for our course.

Chapter 14

ELECTRICAL SAFETY                               638
Walter H. Olson

14.1       Physiological Effects of Electricity   639

Useful figure and definitions of different levels of shock hazard.

14.2       Important Susceptibility Parameters   641

Perhaps a bit too much information for students to process about current needed for hazard.

14.3       Distribution of Electric Power   646

Fairly straightforward description of electric distribution in buildings.  Students should know this already, but most likely don’t.

14.4       Macroshock Hazards   650

Somewhat wordy description of hazards, repeating previous sections.

14.5       Microshock Hazards   653

Important for those who are making direct electrical connections to the heart, which we are NOT.

14.6       Electrical-Safety Codes and Standards   658

As boring as the title makes it sound.

14.7       Basic Approaches to Protection Against Shock   659

Short and nearly contentless.

14.8       Protection: Power Distribution   660

Good description of GFCIs, but the schematic in Figure 14.15 is not explained, and how it works is not obvious.

14.9       Protection: Equipment Design   663

Reasonable description of double insulation and isolation barriers.  Doesn’t seem to indicate that optical couplers are now the dominant method (though I believe they are) for information transfer across the isolation barrier—they give it only as one of three possible options.

14.10     Electrical-Safety Analyzers   667

One paragraph, not much content.

14.11     Testing the Electric System   667

Doesn’t really say how to do it, just that the usual 3-LED tester used by construction workers and home electricians is inadequate.

14.12     Tests of Electric Appliances   669

Basically repeats material from the National Fire Protection Association standards (NFPA99-2005).

Problems   673
References   674

Chapter 14 has some good material on electrical safety, but is probably too much information for the circuits course.  I’m going to have to find a more concise description that students will actually read and remember.

Bottom line

There are bits and pieces of Medical Instrumentation that could be useful to our students, but not enough of the content is relevant to the course to use it as a text and the parts that are relevant are too long for the book to be useful as a reserve book in the library.  It was probably worth my time to read (most of) the book, but I doubt that it will be worthwhile for the students.

Medical Instrumentation, Chapters 7 and 8

As I mentioned in Medical Instrumentation, first 5 chapters and Medical Instrumentation, Chapter 6, I’ve been slogging through one of the potential text books for the circuits course: Medical Instrumentation: Application and Design, 4th Edition. John G. Webster. Publisher: Wiley, 2009. # ISBN-10: 0471676004; # ISBN-13: 978-0471676003.  I need to return the book to the library this week (interlibrary loan periods are short), so I’ll probably just skim the book after Chapter 8, to see if there is anything we can use.


Chapter 7

BLOOD PRESSURE AND SOUND                                 293

Robert A. Peura

7.1         Direct Measurements   295

We’re not sticking catheters into people, so this is irrelevant to our class.

7.2         Harmonic Analysis of Blood-Pressure Waveforms   300

A bad presentation of Fourier analysis, giving only amplitude (not phase), but saying “When we compare the original waveform and the waveform reconstructed from the Fourier components, we find that they agree quite well, indicating that the first six harmonics give a fairly good reproduction.”  You can’t get a reconstruction like that without the phase information, which they never even mention!

7.3         Dynamic Properties of Pressure-Measurement Systems   301

Uses RLC transmission-line circuits to model pressure in a catheter.  The idea of using electrical analogs to model physical systems is an important one, but I’d rather do it with a system that we can actually build and test in the lab.  The number of formulas in this section is large enough that probably only a small fraction of students ever read it.

7.4         Measurement of System Response   308

The describe a way to get the step response of a pressure-sensor-catheter system (by using a bursting rubber membrane to get a step decrease in pressure) and sinusoidal response (using an underwater loudspeaker).  They do not talk about differentiating the step response to get the impulse response, nor using autocorrelation with random excitation to get impulse response.  This section feels like something out of the 1970s.

7.5         Effects of System Parameters on Response   310

Catheter wall stiffness and de-aerating water are important from a fluid dynamics standpoints but are not interesting for a circuits class.

7.6         Bandwidth Requirements for Measuring Blood Pressure   311

Rather trivial discussion of bandwidth, though the mention that looking at the derivative of pressure  increases the bandwidth requirement is an important one that students could easily overlook.  They claim that the amplitude-vs-frequency characteristic of a catheter-manometer system should be flat (to within 5%) for the first 20 harmonics.  For a rapid heart rate of 240 bpm, that means a high frequency of about 80Hz.  That is trivial for electronics, but tough for fluid in a narrow tube.

7.7         Typical Pressure-Waveform Distortion   311

Fairly good discussion of the effects of an underdamped and overdamped system, as well as he effects of air bubbles and “catheter whip”.  Unfortunately, they don’t talk about what “damping” is and seem to confuse it with “inadequate frequency response”.  I would not give this section to someone who didn’t already have a firm grasp of the concepts, as it is likely to lead to serious misunderstandings.

7.8         Systems for Measuring Venous Pressure   313

Medically interesting, perhaps, but nothing new for sensors or circuits.

7.9         Heart Sounds   314

A good description of heart sounds and their correlation to the EKG and blood pressure waveforms.  Talks about the rather non-flat frequency characteristics of stethoscopes, and problems with applying the stethoscope and of leakage at the earpieces.  They talk about the lack of success of electronic stethoscopes on the market and attribute it physicians’ unfamiliarity with the sounds heard through electronic stethoscopes.

7.10       Phonocardiography   318

One paragraph on recording heart sounds.

7.11       Cardiac Catheterization   318

We’re not sticking catheters into people’s hearts!

7.12       Effects of Potential and Kinetic Energy on Pressure Measurements   323

Standard fluid dynamics stuff (Bernoulli’s equation) applied to blood flow.  The stuff about hydrostatic pressure and which way a catheter port points relative to blood flow is undoubtedly important in blood pressure measurements, but is not really relevant to our circuits class.

7.13       Indirect Measurements of Blood Pressure   325

Now we’re finally getting to stuff that could conceivably be useful for the course: non-invasive techniques involving pressure cuffs and listening to the blood flow.  The oscillometric method (which senses the pressure in the cuff) is popular in home blood pressure meters.  I don’t think that we want to put together the cuff and other mechanical parts of a blood pressure meter, but it would give us an excuse for using a pressure sensor.

7.14       Tonometry   330

Measuring pressure in the eye (and in arteries) by force sensors flattening the object being measured. Not really suitable for our circuits course.

Problems   335
References   336

Overall, there is little in Chapter 7 of any use for the circuits class. We could, perhaps, make an electronic stethoscope or oscillometric blood pressure cuff.  The notion of modeling fluid pressure using electronic analogs is an important one, but we can’t use the example here in the lab.

Chapter 8

John C. Webster

8.1         Indicator-Dilution Method That Uses Continuous Infusion   338

We’re not sticking catheter in arteries.

8.2         Indicator-Dilution Method That Uses Rapid Injection   341

We’re not sticking catheter in arteries.

8.3         Electromagnetic Flowmeters   338

We’re not cutting people open to stick $500 cuff probes around arteries.

8.4         Ultrasonic Flowmeters   350

Ultrasonic flowmeters using Doppler shift measurements are kind of cool, but I don’t know that we can get decent transducers for a reasonable price. Hmm,  there is a 7.2MHz transducer that is 22mm in diameter (a bit big for aiming at a blood vessel!) with wire leads for about $4 each in quantities of 5).  I think that the mechanical design problems here could get to be too big for the circuits course.  The electronics is a bit tricky also, as they would have to deal with RF (around 7MHz) and detecting the slightly shifted Doppler return (which is modulated by a noise band, not a simple shift) in a huge carrier background. Probably too difficult for this course.

8.5         Thermal-Convection Velocity Sensors   361

We’re not sticking heated probes into people’s blood vessels.

8.6         Chamber Plethysmography   364

A rather bulky apparatus that we have no reason to build.

8.7         Electric-Impedance Plethysmography   366

We could try building the 4-electrode plethysmograph, but it seems like a lot of trouble for a not very interesting result.  The authors even say “electrical-impedance plethysmography has been used to measure a wide variety of variables, but in many cases the accuracy of the method is poor or unknown.”  We’d probably have to make our own band electrodes also, as the only commercial ones I’ve been able to find are for neonatal EKGs and so are much too small for adults.

8.8         Photoplethysmography   372

This section has the detection of blood flow by shining light through tissue, which I experimented with a bit, but I’ve not found a good way to mount sensors so that they work properly.  They do recommend 940nm LEDs and  phototransistors, in both transmission and reflection setups.  They do mention a problem that I was facing: “large artifacts due to motion saturate the amplifier”.  They point out that when patients are in shock, vasoconstriction reduces peripheral blood flow, so these sensors may not be able to detect the pulses.  Their suggestion of shining the light through the nasal septum is useful in surgery, no doubt, but probably not appropriate for the circuits course.

I’d still like to get this to work reliably without a lot of mechanical setup, because I really want to have a light-sensor application.

Problems   374
References   375

Bottom line

I still don’t think that we can make Medical Instrumentation our main text book, and there isn’t much in Chapters 7 and 8 that we could use.  I wish I could get the light-based pulse sensor working without so much hassle—I’ll have to try it again.

One concept worth looking at is the electrical-circuit analog for mechanical devices.  It might be worthwhile to set up a lab involving pressure measurements at either end of a long tube and modeling the tube as an electrical circuit.  This would give me an excuse for using pressure sensors like the Freescale MPXHZ6250A, which we used in the remotely-operated underwater vehicle as a depth gauge.  That gauge has a 1msec response time (10% to 90% of response to a step input), which is fast enough for most of the experiments I can think of for them to do.

2012 August 9

Medical Instrumentation, Chapter 6

As I mentioned in Medical Instrumentation, first 5 chapters, for the past few days, I’ve been slogging through one of the potential text books for the circuits course: Medical Instrumentation: Application and Design, 4th Edition. John G. Webster. Publisher: Wiley, 2009. # ISBN-10: 0471676004; # ISBN-13: 978-0471676003.
Here are my notes on Chapter 6, which may be the most relevant chapter:
BIOPOTENTIAL AMPLIFIERS                            241
Michael R. Neuman

6.1         Basic Requirements   241
2-page intro about why amplifiers are needed and why input impedance needs to be at least 100 MΩ and gain around 1000. Explains need for bipolar signals and for fixed, calibrated gain.

6.2         The Electrocardiograph   243
Explains how the 10 wires (4 limb wires and 6 chest wires) produce the 12 standard signals of the standard 12-lead EKG. Talks about the heart as a varying electrical dipole, and how the 12 leads provide 60 degree spacing of vectors in 2 different planes.

Defines “Wilson’s central terminal” and explains how it can be used to get differential signals to get 6 directions out of the 4 limb wires.

Gives block diagram of a typical EKG.

Discusses the need for protection circuitry and ability for EKG to recover quickly from defibrillation shocks.

This section looks very valuable for our EKG lab.

6.3         Problems Frequently Encountered   254

Discusses many of the problems of EKG design (and, to a lesser extent, EEG design) caused by large transients, ground loops, and capacitive couple of 60Hz noise.  Again, an excellent section for students to read for the EKG lab.

6.4         Transient Protection    264

Parallel Si diodes or back-to-back Zener diodes to short out voltages that are too high.  (Neon bulbs are also mentioned, but their breakdown voltages seem a little high for EKGs.)

6.5         Common-Mode and Other Interference-Reduction Circuits   266

Describes shielding and driven-right-leg system. The driven-right-leg system has a lower effective resistance for the ground electrode than connecting the leg to ground, by feeding back the common-mode signal.  Because the ina126p instrumentation amplifier does not provide a common-mode output, this approach is not available to us.

6.6         Amplifiers for Other Biopotential Signals   269

Figure 6.16 gives frequency and voltage ranges for EOG, EEG, ECG, EMG, and AAP (axon action potential) amplifiers. EMG amplifiers need higher frequency response than ECG (but not as much low frequency response).

Glass micropipette electrodes may need negative-input-capacitance (positive feedback) amplifiers.

EEGs, because of small differential signals and high gain may need very high CMRR (example give needs 112 dB).

6.7         Example of a Biopotential Preamplifier   274

Gives the circuit for an EKG preamp, using op amps. Does not mention the difficulty of matching resistors accurately.  Does discuss saturation caused by DC offsets (hence the need for small gain), hi-pass filtering after the differential amplifier, and low-pass filter in the final stage.  Also has a shorting switch for recentering the stage after the high-pass filter after a transient that moves it out of the linear region.

The discussion of the design could be useful for our EKG lab, though the details will be different for the student design, since they’ll use a single-chip instrumentation amp and 1 resistor instead of 3 op amps and 7 resistors.

They also cite a 2-electrode design

Bootstrapped two-electrode biosignal amplifier:
Dobromir Petkov Dobrev, Tatyana Neycheva and Nikolay Mudrov
Medical and Biological Engineering and Computing
Volume 46, Number 6 (2008), 613-619, DOI: 10.1007/s11517-008-0312-4

that looks interesting.  It sticks a cross-coupled feedback stage in front of an instrumentation amp, to get a low common-mode impedance with a high differential mode impedance.

Dobrev et al’s two-electrode amplifier that uses feedback into the differential electrodes to reduce the common-mode input impedance. I’ve not tested the circuit myself, but I like the idea of a 2-electrode EKG. This circuit won’t fit on the instrumentation amp protoboard, though, so I may want to redesign that board if we want to encourage designs like this one.  The op amps they chose have somewhat better input bias current and common-mode rejection, but lower gain-bandwidth product than the MCP6002 I’ve been using (we don’t need high bandwidth for an EKG).  It’s going to take me a while to understand this circuit well enough that I can explain every component.  I may want to build and test it also, to see if it really does work as claimed without a 3rd ground electrode.  (Schematic copied from article by Dobrev et al.)

Note: Dobrev et al. claim that the standard ECG bandwidth is 0.01-100Hz, but it looks to me like their reference voltage low-pass feedback may compromise the low end a bit. I may have to find a circuit simulator that I can run on my Mac that can handle these components (I’ve been using the web tool CircuitLab, which has a very limited library of components)

I’m a bit dubious of the need for frequencies below about 0.1 Hz. Heartbeats only go down to about 0.46 Hz for a healthy human, though rates as low as 0.16Hz have been reported in the medical literature (in a patient who died within 12 hours). Still, one doesn’t need the DC component of that waveform, and the interesting parts of the waveform are of much shorter duration. Note: bradycardia is often diagnosed at <60bpm (1Hz) and extreme bradycardia is diagnosed at <40bpm (0.67 Hz), though my resting rate is 42–52bpm (0.7–0.87 Hz)—a low heart rate that I believe I inherited from my father.

6.8         Other Biopotential Signal Processors   275

The described technique for the cardiotachometer seems quaint, using counters and registers, even though they say that “software calculates v_o”—the design obviously dates from the days when A-to-D conversion was expensive (say 25 years ago).  Nowadays, the whole thing would be done in software, with just enough analog amplification and filtering to make the signal suitable for input to an A-to-D input of a microprocessor.

The digital integration for the EMG makes more sense, though I wonder whether RMS makes more sense than mean absolute value.

Signal averaging is introduced for evoked potentials (examples given for EEG or ERG signals, as well as fetal EKG).  Other ways of separating fetal EKG from maternal EKG are discussed.

Vector cardiographs are mentioned, but rather dismissively.

6.9         Cardiac Monitors   282

They say that cardiac monitors typically have a bandwith of 0.67–40Hz, rather than the ?–150 Hz of diagnostic EKGs described in Section 6.2, the 0.01–250 Hz of Table 1.1, or the 0.01–100Hz mentioned by Dobrev.  It seems that there is quite a range of different ideas about what part of the waveform needs to be preserved.

Discussion includes the advantages of implantable monitors (like the Medtronics Reveal implantable cardiac monitor).

Block diagrams for lead fall-off alarms are also included.

6.10       Biotelemetry   287

Very brief mention of telemetry, and even briefer mention of modern methods (like ZigBee and BlueTooth).

Problems   288

References   291

Bottom line

I still don’t think that we can make Medical Instrumentation our main text book, but I like a lot of Chapter 6 (particularly when combined with the better parts of Chapters 4 and 5).  I think we’re going to have to extract and boil down the most useful material, though, as there is a bit too much and the useful details are too scattered to have the students go on a treasure hunt for it in the limited time that library reserves circulate for.  Writing the handout for the EKG lab is going to be a massive undertaking—almost a book chapter on how EKGs work.

2012 August 7

Medical Instrumentation, first 5 chapters

For the past few days, I’ve been slogging through one of the potential text books for the circuits course: Medical Instrumentation: Application and Design, 4th Edition. John G. Webster. Publisher: Wiley, 2009. # ISBN-10: 0471676004; # ISBN-13: 978-0471676003, which is used for a bioengineering course at George Mason University, as I commented on in Looking at bioengineering measurements courses.

I wanted to make notes on each section, so I copied the table of contents from Amazon using OCR software.  Unfortunately, their table of contents seems to have been for a different edition, and I ended up having to edit the page numbers and add section titles by hand anyway.  So far I’ve only read the first 5 chapters, and while the book has some material that would be useful to students in our course, it looks like it would not be a good textbook for the course, as it assumes that the students have already learned what our course is trying to teach.  Actually the book is very inconsistent in its assumptions about the readers, probably because the multiple authors for the different chapters did not do a good job of communicating with each other.  There are huge differences in style and level of detail between the chapters also.  I’ve always disliked staple-gun text books, where different authors write independent chapters, and this one seems to have all the standard faults of such books.
Here are my notes on the first 5 chapters:

Walter H. Olson

Starts with a rather boring anecdote before the first section.

1.1         Terminology of Medicine and Medical Devices   4
Boring list of references.

1.2         Generalized Medical Instrumentation System   5
Vocabulary, not much content.

1.3         Alternative Operational Modes   7
More vocabulary.

1.4         Medical Measurement Constraints   9
Useful table of physiological properties, ranges, and what sensor is used to measure them

1.5         Classifications of Biomedical Instruments   12
Low content (4 classification systems for biomedical instruments), but short.

1.6         Interfering and Modifying Inputs   12
Useful, but brief, description of interfering signals.

1.7         Compensation Techniques   13
Rather generic description of compensation techniques that just waves hands at the problem, while assuming that students already know what a transfer function is and how to solve an equation for negative feedback.  Who is the audience for this? Anyone who can follow the text doesn’t need the vague intro material.

1.8         Biostatistics    16
A list of definitions of common statistics (mean, standard deviation, Pearson correlation).  Not much motivation and not enough to actually teach from.

1.9         Generalized Static Characteristics   19
Definitions of accuracy, precision, resolution, … This looks like a useful collection of definitions for students to learn.

1.10       Generalized Dynamic Characteristics   25
Assumes students are comfortable enough with Laplace transforms to think in terms of transfer functions.  This is unlikely to be true of anyone taking their first electronics course.

1.11       Design Criteria   35
Mildly interesting background material.

1.12       Commercial Medical Instrumentation Development Process   37
Irrelevant to our course.

1.13       Regulation of Medical Devices   39
Irrelevant to our course.

Problems   42
References   43

Overall, there seems to be only a little in Chapter 1 worth having our students read: perhaps 1.4, 1.5, 1.6, and 1.9. If I thought that they could follow it, 1.10 might be useful also.  The style here is not encouraging—the chapter is presented in about as boring a manner as could be devised.  The only other chapter by this author is Chapter 14, Electrical Safety, so I tried not to be too discouraged by the poor writing.  Perhaps we could simply skip this chapter.

BASIC SENSORS AND PRINCIPLES                               45
Robert A. Peura and John C. Webster

2.1         Displacement Measurements   45
Just an intro to the idea of measuring displacement.

2.2         Resistive Sensors   46
2 paragraphs on potentiometers  (but only wire wound, which are a bit old fashioned).

6.5 pages on strain gauges, with a rather confusing explanation of how they work.  Shows bridge circuits, expecting students to already understand them, though they aren’t introduced until the next section.

2.3         Bridge Circuits   53
Bridge circuits are now introduced (after having already been used without explanation) and half a page of voltage results from an unbalanced bridge given without explanation.

2.4         Inductive Sensors   53
Self inductance, mutual inductance, and linear variable differential transformers are mentioned, with considerable space given to LVDTs. While I would like to include an inductance sensor in the course, nothing in the section struck me as a valuable way to introduce the concept. Note that they don’t include dynamic microphones (coil moving in magnetic field) in this category, since those are voltage-output sensors—they don’t include such sensors in their classification scheme.

2.5         Capacitive Sensors   56
Describes capacitance sensing for capacitor microphones and explains why they are not suitable for a lot of physiological measurements (where frequencies lower than 20Hz are needed, but the explanation is a bit too abstract. Does not cover electret microphones and their included FET output transistor, so seems a bit old-fashioned.

2.6         Piezoelectric Sensors   58
A reasonable description of piezoelectric sensors, but assuming a much higher level of EE circuits background than we can assume for our students.  (The examples would be good for the very end of our class, not the beginning.)

2.7        Temperature Measurements  62
A basic intro for why temperature measurement is useful medically. Not very interesting nor informative.

2.8         Thermocouples   63

Misleading description of thermocouples that first talks about a single junction, then assumes that students know that there are two junctions.  Unless you already knew how thermocouples worked, the passage would be nearly incomprehensible.

An inverting amplifier circuit is given, but not explained. It has two crossing wires with neither a connecting dot nor a bridge—an ambiguous documentation style that should never be used in a textbook.  (The wires need to be connected for the circuit to make sense, but the standard for crossing wires without a dot is that they don’t connect.)

The LT1025 “electronic cold junction” is used but not explained.  The LT1025 is not, in fact, a cold junction, but a compensator for correcting for the cold junction being at room temperature rather than 0 C.  I can’t tell if the author knew that well and just explained it badly (given how badly thermocouples were explained) or hadn’t even read the data sheet.

2.9         Thermistors   66

The thermistor plots in Figure 2.15 a are rather hard to read. The explanation of self-heating is pretty good. Only the simplest version of the thermistor resistance equation is given. Differential temperature measurement is described but not well explained.

The notes about use of thermistors seem to be a random collection of factoids, with no coherence.

2.10       Radiation Thermometry   69
The explanation of blackbody radiation is good, but their claim that chopped-beam radiation thermometers are standard seems a bit odd—I find very few chopped-beam IR thermometers on the market.  There are some, and they are more tolerant of ambient temperature changes, but the book falsely implies that they are the dominant method.

2.11       Fiber-Optic Temperature Sensors   74
OK explanation of what these do, though they aren’t very relevant to a circuits course.

2.12       Optical Measurements   74
Another 2-paragraph intro.

2.13       Radiation Sources   75
Figure 2.21 e, referred to in the caption and the text, is not included in the printing.

Describes incandescent and arc lamps fairly well. LED description seems a bit out of date (no mention of blue or white LEDs).

The section on lasers also seems rather out of date—they seem to be talking only about high-power lasers and make the ludicrous claim that semiconductor lasers only operate in the infrared and need to be pulsed. I guess they’ve never seen a red, green, or violet laser pointer.

2.14       Geometrical and Fiber Optics   79
Not relevant for a circuits course.

2.15       Optical Filters   82
Not very relevant for a circuits course.

2.16       Radiation Sensors   83
Pretty good explanation of phototubes, photoresistors, photodiodes, and phototransistors.  Not so clear on photovoltaic devices.

2.17       Optical Combinations   86
A one-paragraph section that seems rather artificially tacked on.

Problems   87
References   88

Overall, Chapter 2 had little of use for our applied circuits course. The classification of sensors could have been useful, if the descriptions had been better and the classification scheme more complete. I’m disappointed that a book that has a 2010 copyright still has parts that read like they were written in 1977 (the copyright for the first edition).  This looks like publisher churn rather than a proper updating of the book.

John C. Webster

3.1         Ideal Op Amps   91
Basic rules for ideal op amps are fairly standard, but they don’t seem to be aware of rail-to-rail op amps, which are fairly common now (particularly for low-voltage, single-power-supply op amps).  Assuming that all op amps operate on ±13v power supplies and are limited to ±10v outputs seems quaint.

3.2         Inverting Amplifiers   93
OK presentation of standard inverting amplifier and summing inverting amplifier, with application of summing amplifier to cancelling a DC voltage bias on one input.

3.3         Noninverting Amplifiers   96
Standard non-inverting op amp circuit.

3.4         Differential Amplifiers   97
Gives common-mode rejection ratio as in the range 100 to 10000, without using the usual dB scale.  The cheap chip I’ve been using (INA126P) has a minimum common-mode rejection of 83 dB (which is 14000) and typical of 94dB (which is 50000), and for $10 the INA118P has a typical CRR of  120dB (1000000) at a gain of 100, so their numbers seem rather dated.

Gives both 1-op-amp and 3-op-amp differential amplifiers, but no 2-op-amp circuits (the INA126P is a 2-op-amp differential amplifier).

3.5         Comparators   100
Reasonable explanation of hysteresis.  I would have preferred some explanation of the dynamic behavior also, as op amps make rather slow Schmitt triggers, which can make a huge difference in some applications.

3.6         Rectifiers   102
2-op-amp circuit with 4 diodes, a resistor, and a potentiometer to make a “perfect” full-wave rectifier circuit.  Also a one-op-amp circuit (which really needs both an input and an output amplifier, since it has a low input impedance and requires a constant load). The application given (using with an integrator to quantify the amplitude of electromyographic signals) seem ok, but I suspect that it would be easier and cheaper to do that in a microprocessor nowadays.

3.7         Logarithmic Amplifiers    103
OK circuits, but probably not all that useful.  It would have been better if an example of “device with logarithmic or exponential input-output relation” had been given, as I can’t think of such a sensor off the top of my head.

3.8         Integrators    104
Standard integrator circuit.  Example of use as a charge amplifier for piezoelectric transducer.  Good explanation of the need to restore initial conditions because of drift.

3.9         Differentiators    107
Standard circuit.  Mentions problems with oscillation and noise amplification, but doesn’t say what to do about them. Gives application to detection of R wave in an EKG, though everyone would do that in software nowadays.

3.10       Active Filters    108
Standard one-op-amp low-pass, high-pass, and band-pass filters. Students would need to understand transfer functions to understand how these work.

3.11       Frequency Response    110
Starting to look at non-ideal op amps. Good explanation of loop gain, gain-bandwidth product, and slew rate.

3.12       Offset Voltage    112
Offset voltage is explained, but the nulling pot is rather vaguely described—not all amplifier chips have the “terminals indicated on the specification sheet” for doing external nulling.  (The ones I’ve been using, for example, do not.)

3.13       Bias Current    114
Their use of old op amps makes for some rather large bias currents (200 pA, rather than ±1pA).  The INA126P instrumentation amp I’ve been using, however, has an enormous bias current of -10 nA. Their explanation of compensation for bias current and calculation of noise due to variations in bias current is more confusing than enlightening.

3.14       Input and Output Resistance    115
Reasonable discussion of input and output resistance, with appropriate caveats about how other limitations (input bias current and output current limits) make the calculated input and output resistances rather useless.

3.15       Phase-Sensitive Demodulators   117
The transformer-based ring demodulator seems like rather old tech. Even the solid-state part they mention (1495, a 4-quadrant multiplier) is obsolete and no longer available.  More recent parts like the AD633 4-quadrant multiplier or HFA3101 RF mixer would make more sense to describe. It looks like this section has not been updated for 15 years.

3.16        Timers                  120
Describes using a 555 timer to make an oscillator.  This is not really any better than using an op-amp relaxation oscillator and hardly seems worth the trouble of adding to the book between editions.  They don’t explain the 555 in any detail, so I fail to see the benefit added by this section.

3.17       Microcomputers in Medical Instrumentation   122
Reads like an ad for LabVIEW.  Has no content other than to say that everything is done in microprocessors these days (contradicting a big chunk of hte chapter).

Problems    123
References   125

Chapter 3 has more-or-less standard op-amp circuits, with a few rather old-fashioned choices thrown in.  It could be mildly useful, but I’m pretty sure that there are dozens of books that present the same material better.  All circuits stuff that comes before op amps is completely lacking from this book, which lowers its value for our course enormously.  At this point, it is clear that this book will not be useful for at least the first half of our course.

THE ORIGIN OF BIOPOTENTIALS                              126
John w. Clark. Jr.

4.1         Electrical Activity of Excitable Cells   126
A good, basic introduction to where voltages in the body come from. I think that the bioengineers would benefit from reading this, and it would tie into their chemistry and biology courses well.

4.2         Volume Conductor Fields    135
This section is not as clear, but could still be useful in a run-up to the EKG lab.

4.3         Functional Organization of the Peripheral Nervous System   138
Background material that isn’t really relevant to the course.

4.4         The Electroneurogram (ENG)    140
Useful to medical people, but a bit irrelevant for this course. There is no way that we’re going to hook up 100v stimulators to students!  The chances of them doing real damage to themselves by using pulses longer than 300 microseconds is too high. (I’ve also had treatment with electrical stimulation when Ihad ulnar tunnel inflammation—it can get quite painful if the level is set too high.) I also think that having them try to pull out 10 μvolt signals from the noise is too challenging for a first circuits course.

So while this section has some cool background material, there isn’t much in it directly applicable to the course.

4.5         The Electromyogram (EMG)    144
Explains why EMGs are often done with needle electrodes rather than surface electrodes, but otherwise not of much use.  We’re not going to be puncturing the skin in our course.

4.6         The Electrocardiogram (ECG)    139
Somewhat detailed explanation of how the electrical system of the heart works.  It is clear that modeling the heart is one of the author’s loves, and this material might be useful as background before the EKG lab.

4.7         The Electroretinogram (ERG)    158
No way that we are putting electrodes on or in the eye.

The EOG (electro-oculogram), which attempts to measure eye movements from electrodes on the bridge of the nose and the temple is interesting,as it requires DC amplification of small signals.  I found a DIY EOG project—they use a $10 instrumentation amp (the INA118P).  I’m not sure whether the better specs of that part are needed for this application, or whether the $2.50 INA126P that I’ve been using would suffice (they have the same pinout). I’ve not priced small disposable electrodes of EOGs, but the ECG ones we have are too big for the bridge of the nose.

4.8         The Electroencephalogram (EEG)    163

I’ve looked at the open-source EEG stuff before, but I was having enough trouble with the EKG circuits, that I decided not to tackle EEG.  Now that I have EKG circuits that work reliably, I may revisit the EEG.  The difficulty of pulling out 50–100 μvolt signals from the noise due to facial muscles and so forth may make this lab impractical.  Unlike the EKG, where a functioning circuit provides a characteristic output that is easily recognized, it is difficult to tell whether an EEG is working correctly, especially as the subject generally needs to be lying down, relaxing, with their eyes closed, so students would have a hard time watching the oscilloscope while taking their own EEG.
Input electrodes can be a problem also—I don’t think that there’s a cheap disposable electrode that works well (unlike the EKG).

This section has way too much info on brain structure for my taste.  There are good subsections on the brain waves and different “montages”: differential, referential, or “Laplacian” reference voltages for the signals.
4.9         The Magnetoencephalogram (MEG)    181
Superconducting quantum interference devices (SQUIDs) are well beyond the scope of this circuits class.

Problems    182
References    186

Overall Chapter 4 had some useful material for our students—particularly on the sources of biopotentials and to a lesser extent on how the EKG signal is related to the internals of the heart.  It might be worth having students read bits of this chapter before the EKG lab (put the book on reserve in the library?).

BIOPOTENTIAL ELECTRODES                      189
Michael R. Neuman

5.1         The Electrode-Electrolyte Interface    189
Good description of half-cell potentials.

5.2         Polarization    192
More useful electrochemistry.

5.3         Polarizable and Nonpolarizable Electrodes    196
A good explanation of why platinum and Ag/AgCl electrodes are used and what the difference is between them.  Describes both electroplated and sintered Ag/AgCl electrodes (though not the “bleach” method for creating AgCl layers on silver).
I found some good instructions for both electroplating and chlorine bleach treatment from Warner Instruments:

Cleaning the Ag+ wire before chloriding

The wire should be cleaned before chloriding. An un-chlorided wire can simply be cleaned with EtOH and rinsed with H2O before proceeding. A previously chlorided wire should be wiped with dilute HCl to remove the old coating, then rinsed in EtOH and H2O.

Chloriding the Ag+ wire

There are two methods in common use to chloride a silver wire. These are the putative electrical and chemical methods. Both work very well but the electrical method yields a deeper coating.

Electrical method

Electrical chloriding of Ag+ wire is achieved by making it positive relative to a solution containing NaCl (0.9%) or KCI (1 M). One way to achieve this is to pass a current at a rate of approximately 1 mA/cm2 for about a minute, or until the wire is adequately plated. (For example, to chloride a 2 cm length of a 0.25 mm Ag+ wire (this is the diameter of the wire used in Warner electrode holders) requires 0.15 mA of current.) The color of a well plated electrode will be light gray to a purplish gray. While plating, occasionally reversing the polarity for several seconds tends to deepen the chloride coating and yield a more stable electrode.

Chemical method

An alternate to the electrical method is to immerse the wire in Clorox bleach until a light gray color is observed (typically 10–15 minutes is sufficient). At a minimum, this simpler method is commonly performed at the beginning of each day’s work.

5.4         Electrode Behavior and Circuit Models   202

A simple circuit model for an electrode is given, and the effect of different thicknesses of AgCl on an electroplated electrode is shown.  If we have students electroplate Ag/AgCl electrodes, this would be very useful information for them. They also provide an example showing how to estimate the four parameters of their electrode model from simple measurements.

This section looks useful to our students.

5.5         The Electrode-Skin Interface and Motion Artifact   205

The discussion of the electrode-skin interface is useful, and the suggestion to reduce the resistance by stripping off layers of the stratum corneum with Scotch tape seems useful. (I did some searching on line, and the standard Scotch Brand “magic tape” seems to be commonly used.)  This technique seems more suitable for our course than abrading, puncturing, or using acetone wipes.

5.6         Body-Surface Recording Electrodes   209

A good description of electrode designs, including the type we expect to use for the EKG lab.  The “neonatal” electrodes are also cheap (about 30 cents each) and may be less irritating than the ones I’ve been using, which start to itch after several hours.

5.7         Internal Electrodes   215

We won’t be using implantable electrodes, but students might be interested in knowing about them.

5.8         Electrode Arrays   220

Mildly interesting background material about electrode arrays.

5.9         Microelectrodes   222

The info about micropipette electrodes is directly relevant to the nanopipette research at UCSC.  The reference to negative-capacitance amplifiers (Section 6.6) may be useful.

5.10       Electrodes for Electric Stimulation of Tissue   231

Not relevant for this class, though the mention of carbon-filled rubber electrodes is mildly relevant, since we might have used them for the EKG (if we wanted a more long-term connection than the disposable electrodes).

5.11       Practical Hints in Using Electrodes   233

Basic, sound advice (like not using dissimilar metals and being aware that the insulation may not work as well when wet).

Problems   235
References   239

Chapter 5 looks like useful information for our students (again, mainly for the EKG lab).

Bottom line

I don’t think that we can make Medical Instrumentation our main text book.  It doesn’t have anywhere near enough of the basic circuits material, and the op-amp section is not wonderful. Big chunks of the book are showing their age, and the 4th-edition revisions aren’t nearly extensive enough to justify a recent date.  If we’re going to use an ancient book, we should use one that is available cheap.

There is some good material on biopotentials and EKGs (and I expect more EKG material in Chapter 6), but these are not enough to justify its use as a text book for this course.  They may be enough to justify putting the book on reserve in the library, though the reading time is large for reserve material.  We might have to write our own shorter handout covering just the high points of this material.

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