Politicians complaining about the press are like sailors complaining about the sea.
— Winston Churchill
Figure 1: My Short-Term Solution to Stop Condensate from Freezing in My Septic System.
Minnesotan's have endured a cold winter with relatively little snow, a situation that causes the ground to freeze deeper than expected. In northern Minnesota, we plan for 60 inches of frost depth, but this year the frost has gone much deeper. For those cabins with condensing furnaces, this extra frost depth has resulted in many frozen septic lines. This winter, I have frozen both my cabin and garage septic lines.
As I have discussed in a previous post, these furnaces generate ~1 gallon of condensate for every 100,000 BTUs of propane burned. On the coldest days, my garage furnace produces 5 gallons of condensate per day, which means that I have a constant trickle of water flowing into my garage septic line. Unfortunately, this flow rate is so small that the water only slowly moves through the pipes. This slow movement of the condensate means that it can freeze, resulting in a clogged septic line.
I first tried a 1-liter condensate pump, which stores 1-liter of condensate before putting it out in a surge. The idea is that 1-liter slug of water will be less likely to freeze than a trickle. Unfortunately, a 1-liter slug of water was not large enough, and it froze in the pipe.
Figure 1 shows the approach that worked. I have the 1-liter condensate pump fill a 110-litter tub. This tub contains a sump pump that puts out a surge of about 40-liters. This surge was sufficient that it did not freeze. Both my garage and my home have the same setup.
Long-term in the garage, I will pound out the concrete floor and put in a sump basket. The sump will be lower than my furnace, which will allow me to use gravity to feed the sump with condensate, eliminating the need for the 1-liter condensate pump. I will put the sump pump in the basket, which will then pump 40-liter surges into my floor drain. Unfortunately, I cannot install a sump pump in my house because its concrete floor contains in-floor heating tubes. For the house, my short-term solution is also my long-term solution.
The following video shows how to install a sump pump in a concrete floor.
Figure 2: Good Video On Installing a Sump Pump in a Concrete Floor.
If you wanna hire great people and have them stay working for you, you have to let them make a lot of decisions and you have to be run by ideas, not hierarchy. The best ideas have to win, otherwise good people don't stay.
I was watching physicist Michio Kaku on CSPAN last Sunday night talking about his new book The Future of Humanity. I like watching authors speak on CSPAN because they provide an extended interview format for authors. In this interview, the interviewer Brian Lamb mentioned a factoid as part of a question that I thought was worth investigating.
You say in your book that 544 humans who have been in space and that 18 of those have died. What do those numbers mean to you?
Table 1: Space Travelers By Country.
Of course, the number of people who have been in space is changing with every flight into orbit, and this type of fact is guaranteed to be obsolete immediately after publication. I thought I would investigate the number of people who have been in space and how many have died as part of their mission. These numbers were easier to verify than I would have expected.
The Wikipedia has a page that contains a comprehensive list of the people who have been in space. Using Power Query, I downloaded this list, did some routine data clean up, and generated the data summary shown in Table 1. As of this date, 558 people have gone into space. You can see that the US has put the most people into space, which is most likely because the space shuttle could carry more people than the Soyuz spacecraft.
The Wikipedia also has a page with a list of those who have died on space missions, not all of which reached space. As with Table 1, I downloaded the data, cleaned it up, and generated Tables 2 and 3. Table 2 contains the name of those who died going on space missions, and Table 3 shows the number of space fatalities by vehicle. For those who are interested, my Excel workbook and data are here.
As an aside, I watched a TV show years ago that was hosted by Dr. Kaku in which he was the guest of a US Army unit. The US Army drafted Dr. Kaku during the Vietnam War, which ended before he completed his infantry training. During his stay with this unit, he demonstrated some physics while wearing a US Army uniform. You could tell that both Dr. Kaku and the soldiers enjoyed his visit. He seems like a good man.
So, in the face of overwhelming odds, I'm left with only one option: I’m going to have to science the shit out of this.
— Mark Watney, The Martian. I love this quote.
Figure 1: Appendix Opening. This is not a photo of mine. (Source)
I had a colonoscopy yesterday, and it was a great learning experience. I am fortunate that the anesthetic they gave me had little effect, and the doctor was open to answering questions from an inquisitive patient. It probably helped that the doctor was a mechanical engineer that decided to go into medicine – we had lots to talk about. I found it funny when he mentioned that he did not like engineering work on optics – of course, much of my life has been spent designing optics. In the course of this doctors daily work, he uses optics all day long. His gear was from Olympus, some of which is manufactured in Brooklyn Park, Minnesota, which is near my home. Minnesota is known for its medical technology.
Here are the notes I took on the procedure.
What is the basic colon inspection procedure
The doctor told me that they put the probe in all the way to the appendix without really doing any observations. The colon sort of hugs the probe and you cannot see much. Once the probe gets to the appendix, they inflate the colon with CO2 and do their inspection on the way out.
How long is the colon?
Around four feet long – he said the length is correlated with your height. Here is a good image of the colon. You can see the appendix at the beginning of the colon.
While in my upper colon, the doctor told the nurse he wanted to use CO2 to inflate that section. I asked the doctor why CO2 instead of air. He said that CO2 is absorbed by the colon into the bloodstream very quickly and you just breath it out. Air is not so quickly absorbed and, if used, would leave you feeling bloated after the procedure.
Has the doctor ever seen an infected appendix?
He said that he has seen two during his years of practice (I would put the doctor in his late 40s). He said that an infected appendix is no issue as long as it can drain into the colon. An infected appendix will eventually heal as long as it can drain. You get into trouble when an infected appendix cannot drain and it ruptures.
I was floored at how much the technology has improved since my last colonoscopy.
My last colonoscopy was 9 years ago. The screen images back then were low resolution and black and white. These were high-res and in color. The level of detail was amazing. He controlled how the probe moved using a hand control that reminded me of the old hand controls used for remote manipulators.
I have seen two types of polyp removal.
Nine years ago, I had a mushroom-room shaped polyp and it was removed with a lasso-type instrument that both cut and cauterized the polyp. The doctor extracted the polyp, put it into a bag, and sent it for tests (no issue). I had three very small polyps this time. A very small pliers-like instrument was inserted and he just grabbed the polyps, twisted them to remove them, bagged them, and sent them in for tests.
Do people ever come in that were not "cleaned out"?
I was told it happens all the time. They have to go back home and take more laxatives. They colon has to be cleaned out for the doctors to do their work. Personally, I cannot imagine someone following the procedure and not being cleaned out.
Unfortunately, although the electrical and thermal differential equations are analogous, it is erroneous to conclude that there is any practical analogy between electrical and thermal resistance. This is because a material that is considered an insulator in electrical terms is about 20 orders of magnitude less conductive than a material that is considered a conductor, while, in thermal terms, the difference between an 'insulator' and a 'conductor' is only about three orders of magnitude. The entire range of thermal conductivity is then equivalent to the difference in electrical conductivity of high-doped and low-doped silicon.
— Clemens J. M. Lasance, Thermal Engineer for Philips. As an electrical engineer, I use lumped parameter models with confidence because I know that my insulators really insulate. The thermal engineer does not have that luxury.
An engineer stopped by my cube today and asked a question about how to estimate the junction temperature of a part on a circuit card that may have an over-temperature problem. Using the common thermal resistances (θJA and θJC), he was obtaining nonsensical results. This problem was a good illustration of the difficulties present in estimating Integrated Circuit (IC) junction temperatures using the commonly supplied thermal resistances.
I will show how I went about estimating the junction temperature of this device and why the methods usually used can provide unrealistic results. My results are estimates, but show that the junction temperature of the ADN4612 is significantly lower than its maximum rating and does not warrant any further analysis. If it were close, I would bring in a mechanical engineer to perform a more detailed thermal analysis.
With respect to ADN4612's junction temperature in this application, the following characteristics are relevant :
power dissipation: PD = 3.5W
top of case temperature: TTop = 105°C (measured with thermocouple)
via temperature under part: TPCB = 82°C (measured with thermocouple by a via under the part)
package: 88-pin Lead Frame Chip Scale Package (LFCSP )
maximum allowed junction temperature: TMax = 125°C/W
Issues Using Common Thermal Resistances
IC specifications commonly give two thermal resistances, θJA and θJC. These specifications are useful, but frequently misused. The key to their proper use is to understand how they are measured. θJA is measured on a standard PCB as defined by JEDECJESD51-2. Since every circuit board design is different, θJA is only useful for comparing the relative thermal performance of different packages. It is not useful for predicting component temperatures on a specific PCB and environment that are different from the test configuration.
θJC is measured in a special jig that forces all the heat through some area on the IC's case. For most ICs, the heat is forced through the top of the case. This makes sense if you are going to put a heat sink on the part and your plan is for most of the heat to go out the top. In the case of the ADN4612, it has a copper slug on the bottom of the part. θJC for the ADN4612 is measured by forcing all the heat through the bottom of the part and into the PCB. Again, this situation is not what actually occurs – the part will dissipate heat into the environment through multiple paths (bottom, top, leads).
Ideally, we would thermal models that provided use thermal resistances for all the possible paths for heat to leave a part. These models, called compact thermal models, do exist, but most vendors do not supply all the required parameters (e.g., Figure 2).
Figure 2: Example of a Compact Thermal Model for an IC (also known as Delphi model). (Source)
While compact thermal models for every part would be great, most ICs are not going to have temperature issues. An electrical engineer wants a rough estimate of the junction temperature to determine if he needs to bring in a mechanical engineer for a more detailed analysis of a specific part. For this approximate type of work, I prefer to use Psi-JT (ΨJT). This parameter is NOT a thermal resistance and is referred to as a thermal characteristic. It also is defined in JESD51-2. The standard allows for making a simple linear estimate of a part's junction temperature in a typical application using Equation 1.
TJ is the IC junction temperature.
TTop is the measured case temperature on the top of the part (the easiest place to get a measurement).
PD is the part power dissipation.
ΨJT is the thermal characteristic between the junction and the top of the IC case.
Unfortunately, Analog Devices did not provide ΨJT on their datasheet. This is where a bit of digging comes in …
Because the datasheet did not contain ΨJT, I started using my usual search engine to do some specification hunting. It turns out that I did find a couple of references to ΨJT for similar packages:
an Analog Devices forum discussion on the 24-pin version of this package, which gave a 0.9°C/W for ΨJT.
an Analog Devices forum discussion on the 20-pin version of this package, which gives a simulated value of 0.27°C/W for ΨJT. The difference between a simulated value and measured value like this does not shock me at all.
We can also calculate an approximate ΨJT value using the method I outline on this blog post (Figure 3).
Figure: 3: ΨJT Estimate Using Approximation.
For my calculations below, I will assume the worst-case ΨJT value I found of 0.9 °C/W.
As a cross-check, I can also make an approximation using ΨJV: junction-to-PCB via thermal characteristic, which I obtained from this chart (Figure 4).
Figure 5 shows my calculations to estimate the junction temperature for the ADN4612 using two different parameters: ΨJT and ΨJV.
Figure 5: Two Ways to Estimate Junction Temperature.
I view my two estimates of junction temperature (108°C and 103°C) as reasonable close for this type of approximate calculation. Both methods show that the part is not operating near its junction temperature limit of 125°C, which is what I needed to know.
I do wish the semiconductor vendors would provide designers with better thermal data and models that would make applying their parts easier. I should not have to search the web and crawl around forum discussions in order to intelligently use a vendor's part.
Knowledge consists in the search for truth ... it is not in the search for certainty.
— Karl Popper. I have always found his work on the philosophy of science interesting. He is best known for his belief that scientific concepts must be falsifiable.
Figure 1: Deceptive Image of an Asteroid Passing Extremely Close to the Earth. (USA Today)
Newspapers often talk about Near-Earth Objects (NEOs) that are passing "close" to the Earth. To increase the number of clicks, the articles usually include an image implying that the NEO is very close to the Earth. I find these articles a bit irritating.
This morning at 2:53AM Eastern Standard Time, asteroid 2017 VR12 had its closest point of approach to Earth, which was ~4x the distance from the Earth-to-Moon. It is not considered an impact threat. USA Today published an article that included Figure 1, which implies a very close pass. That is simply not correct.
To give you some perspective, let's examine Figure 2, which is a picture of the Earth-Moon system as seen by an asteroid-sampling spacecraft called OSIRIS-REx.
Figure 2: Earth-Moon System from 3 million miles away. The Moon is 60 Earth radii distant from the Earth. Asteroid 2017 VR12 is ~4x this distance from the Earth at its closest point. (NASA)
The article also mentioned that the asteroid "could be as big as Empire State Building". I thought I would show how you can do that calculation for yourself (Figure 3). The Empire State Building is 443.2 meters tall, which is roughly the maximum equivalent spherical diameter of 2017 VR12. The uncertainty in size is large because the albedo of asteroids is so variable.
Figure 3: Calculations That Show 2017 VR Could Have an Equivalent Radius Similar to the Empire State Building.
The young man knows the rules but the old man knows the exceptions.
— Oliver Wendell Holmes Jr.
Figure 1: View of My Cabin as I Walk From My Garage.
My cabin construction project is now complete. My wife and I are now beginning to furnish our new home, which will take some time. I continue to work on the garage construction myself, which will take until sometime in May to finish. Overall, our planning was good and there were no major surprises. The one area of difficulty that I did not fully appreciate is the remoteness of the site. Before you go to the site, you need to plan out every possible tool or part that you will need while there.
This is a huge, multi-year project that I am relieved to say the house portion is complete – the garage still needs a bit of work. My plan is to retire at this site in 5 to 10 years and spend my time designing hardware, writing software, and building furniture. I hope that my granddaughter will get to spend quite a bit of time here with her grandparents.
Some basic home details:
2100 square feet
no basement, concrete slab on ground with in-floor heating
— Sir Winston Churchill, quoting the reply of the then elderly Duke of Wellington when a friend asked him, 'If you had your life over again, is there any way in which you could have done better?'
Figure 1: People Curling in Northern Minnesota. (Source)
I spend a lot of time in northern Minnesota now that I have a home there. I have been surprised as to how popular curling is in the area (Figure 1). The US curling team at the 2018 Olympics is dominated by people from northern Minnesota. I also notice that there are quite a few Minnesotans participating in the games' other sports – the numbers are large enough that the New York Times has even written an article called "Team USA? More Like Team Minnesota" on the topic (PDF of the article). Our state does not have a huge population, ~5 million, and most of that population is concentrated around Minneapolis and St. Paul. The northern part of the state is only sparsely populated as it is covered with national forests and wilderness areas.
To understand the participation of Minnesotans in the Olympics, I grabbed an Excel file from the US Winter Olympic Team web site and generated a couple of pivot tables, which I show below. My workbook is include here.
Figure 2: Top Ten Home States for US Olympic Athletes.
California contributes the most athletes to this year's Olympic team, followed by Colorado and Minnesota (Figure 2). Since Minnesota has no mountains, alpine events are not our strength – though Lindsey Vonn is from St. Paul and first skied here at Buck Hill.
The big snow sports here are hockey, cross-country skiing, and curling. You see this reflected in the athletes we send to the Olympics (Figure 3). Biathlon is a combination of cross-country skiing and shooting, which are two common passions here.
At this point, the Minnesota athletes have brought home medals in curling, hockey, and cross-country.
Figure 3: Minnesota Participation in Olympic Sports.
For my family, skating and hockey became a passion first for my children and then for me – this is the reverse for most families. My dad was a hockey player and ice dancer, but I never had any interest early on in either sport. My children saw the movie The Mighty Ducks, and they became driven to skate. I learned to skate and play hockey on the kiddie ponds next to the rinks where my children were practicing.
Table of Athletes
I included a subset of the Olympic spreadsheet here for any general searching that I want to do.
Figure 1: I have decided that it is time for a new job. (Source)
My company is changing its approach to hardware development, and after much soul-searching, I have decided to volunteer for layoff. I do not have any immediate plans – it is just time for a change. I will continue to write on technical topics because math, electronics, and software are in my blood.
I fell in love with electronics when I was five-years-old after my neighbor showed me a schematic. I thought it was some weird language that I needed to figure out. My first projects involved building kits from Radio Shack, Heathkit, and Lafayette Radio that I paid for using my income as a paperboy. I also started doing circuit-based science fair projects. It all culminated with me studying electrical engineering and working in this field for my entire career. Even after these many years, my passion for technology of all sorts continues unabated.
If you know of any jobs that would be appropriate for someone like me, please leave me a note here or on my linkedin page. My wife's job is covering my benefits, so either a contract or employee position would work.
Our educational system is like an automobile which has strong rear lights, brightly illuminating the past. But looking forward, things are barely discernible.
— Hermann Oberth, German rocket theoretician, describing the German education system in the 1920s. He was bitter because his doctoral thesis on rocket propulsion was deemed utopian. His work became the basis of all spaceflight today. In my opinion, his criticism of the German educational system could be applied to the US education system today.
Figure 1: Japan's SS-520 rocket. It is reported to be the smallest rocket capable of putting a payload into orbit. (Source)
I just read a news article about Japan launching a 3 kg satellite into orbit using a 9.7-meter-long, two-stage rocket called the SS-520 (Figure 1). The 9.7 meter length was interesting to me because I recalled an Air & Space magazinearticle from 1999 that stated that the smallest rocket capable of achieving Earth orbit would be "about 30 feet long." Since 9.7 meters is 31.8 feet long, it appears that Japan's SS-520 is very near the lower size limit for rocket that can put an object into Earth orbit.
The size limit for an orbital rocket is driven by the amount of momentum lost because of atmospheric drag. As with artillery projectiles, larger rockets are more efficient in retaining momentum against drag. For a given shape, larger rockets are more aerodynamically efficient because frontal area increases by the square of the linear dimensions and volume (and mass) scales by the cube of the linear dimensions (see this detailed discussion). Drag is a function of the frontal area of the rocket, thus larger rockets have more mass (and momentum) relative to their drag. Another challenge with implementing a small launch vehicle is the difficulty of efficiently implementing a high specific impulse, liquid-fuel system because of the overhead of all the pumps, plumbing, and cooling.
Because I am still tied up with my cabin project, I have not gone through the minimum-sized orbital rocket calculations myself. Air & Space magazine states that:
A terrestrial rocket has to push through a plug of air equivalent to a 30-foot column of water, and physics dictates that the smallest vehicle capable of moving all that atmospheric mass without paying a penalty in momentum is about 30 feet long.
Historically, the orbital launch market has been dominate by customers who want to put large payloads into space. The advent of CubeSats has created a market for these small rockets. For example, a company called Rocket Lab uses their Electron rocket to launch small groups of CubeSats.
NASA has been researching the smallest rocket that can return a sample from Mars to Earth. According the Air & Space magazine article, the smallest orbital rocket is "about the size of a pencil" for essentially zero payload. NASA's Mars return mission is targeting a 1 pound payload and the mass is about 170 kg. Having lower gravity and a much thinner atmosphere make the job of getting into Mars orbit much easier than getting into Earth orbit.
People have been discussing these small rockets for many years. In fact, people have tried to motivate innovation in this area with the N-Prize, which is focused on putting a small payload (10 - 20 grams) into Earth orbit for less than 1000 £ . For an excellent discussion on micro-rocketry, see this forum thread. The following Google talk on microlaunchers is also useful.
Figure 2: Microlaunchers – The Case for a New Generation of Very Small Spacecraft.
As I have mentioned in other posts, I am building a large garage in northern Minnesota (Figure 1). I would show you some pictures of the interior, but I have promised my son that I will not post anything that could ruin his surprise when he sees it in April. As part of this construction effort, I am using quite a bit of electrical conduit. Conduit consists of metal pipes (often called EMT) through which the wires pass and it must be bent to go around any barriers it encounters. Conduit is a very efficient way to wire a working area because it directly attaches to the wall and does not require opening holes in drywall and repairing the damage. Conduit can also be updated and modified easily by running new/additional wires through it.
Figure 2: 4-Point Saddle Bend Around An Obstacle. (Source)
I am going to review the process for running conduit around an obstacle using a 4-point saddle bend, which entails bending the conduit into a trapezoidal shape for passing around the obstacle (Figure 1). Electrical handbooks contain tables that tell electricians how to measure along the conduit so that the bend will go around an object of a given depth. In this post, I will provide simple formulas for this bend and will use these formulas to regenerate a commonly seen table for conduit bending.
For those who like to follow along, my worksheet is here.
In this post, I will duplicate a conduit bending table that I saw in this excellent reference article. The table is shown in Figure 3, which has units of degrees for angles and inches for length.
Figure 3: Bend Table That I will Duplicate in Excel.
Conduit Bending Video
Figure 4 shows a conduit bending video by a local trade school (Dunwoody) that I think is first-rate. The instructor covers both 4-point (trapezoid) and 3-point (triangular) bends. My focus in this post is the 4-point saddle bend because that is what I am dealing with in my garage construction right now.
Figure 4: Good Briefing on 3-Point and 4-Point Saddle Bends.
Conduit Bending Formulas
Conduit Bending Formulas Ignoring Bend Radius
There are two formulas that I need to generate: (1) shrinkage, which is the reduction in horizontal length caused by the bend; (2) bend distance, which is the horizontal length of the bend region. Figure 5 illustrates the geometry of the situation.
Figure 5: Key Conduit Bending Formulas Ignoring Bend Radius.
Applying basic trigonometry to Figure 5, we can derive Equations 1 and 2.
BD, Bend Distance is the horizontal distance between bends.
BO, Bend Offset is the depth of the obstacle to be passed over.
Θ is the angle of the bend.
S, Shrinkage is the effective reduction in horizontal conduit length because of the bend. Essentially, it is the difference in length between the hypotenuse and the base of a triangle.
I will use these equations to generate the table shown in Figure 3.
Conduit Bending Formulas Compensating for Bend Radius
Again, there are two formulas that I need to generate: shrinkage (Equation 3) and bend distance (Equation 5). An additional formula for the straight pipe length is also provided (Equation 4). Figure 6 illustrates the geometry of the situation and the associated formulas. The radius of the conduit bender, called R, will vary for each conduit bender. It normally is stamped on the bender, or the information is available in the vendor's literature.
Figure 6: Key Conduit Bending Formulas (Compensating for Bend Radius).
Applying basic trigonometry to Figure 5, we can derive Equations 3, 4, and 5. Note that BD is defined slightly differently in that it represents the center-to-center distance between the bends.
Equations 3 - 5 are functions of the bend radius of the conduit bender. Because conduit benders can have different bend radii (see Figure 7), this means that using a single table for all conduit benders may result in some error – particularly for large bend offsets. Ideally, we would build a table for the conduit bender being used. I include this table with bend radius as a parameter on a worksheet in the Excel workbook associated with this post.
Figure 7(a): Klein™ Conduit Bender with a 4" Bend Radius.
Figure 7(b): Ideal™ Conduit Bender with a 5.25" Bend Radius.
My focus here is on generating the traditional conduit bend table. In my workbook, I also include a tool using a more exact model.
There are a number of ways I could generate this table using Excel. The approach I chose was to:
Generate a table of values for bend offsets of 1 inch. I call this my "reference table" because it is used for all subsequent calculations.
Generate separate tables of shrinkage and bend distances.
Collate shrinkage and bend distance columns by bend angle (Θ).
I chose this approach because I wanted to experiment with arranging columns by using a helper row containing the ordinal number of each column and doing a horizontal sort.
For demonstration purposes, I also included a tab where I used formulas to fill down the columns. A third tab was includes the conduit bender radius as a parameter.
Figure 8 shows the shrinkage and bend distance formulas evaluated for a 1-inch bend offset (i.e. obstacle height), rounded to the nearest 1/16th of an inch. These values can be used as scale factors for other obstacle heights, which is exactly how the table in Figure 3 was generated.
Figure 8: Reference Bend Table.
Full Table Generation
The table shown in Figure 3 is generated by multiplying the bend offsets by the scale factors in Figure 9. I used Excel tables to perform this action.
Figure 9: My Excel Version of the Conduit Bend Table.
I was able to duplicate the original table. I will be using this table for some conduit bending this weekend.
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