Monthly Archives: March 2024

Vacuum Systems-  The Wrong Stuff

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The cost of the learning curve.: hoses and fittings that ended up NOT being helpful in reaching my target vacuum.

My idea of creating a vacuum was terribly simplistic.  Just run a pump until you reach your desired vacuum, right?.  Well… I learned that there is much more to it. 

First, there are different degrees of vacuum, categorized by how difficult it is to attain them.  The easiest can be obtained by a mechanical pump, a piston, or equivalent, pushing air molecules from the chamber to the outside, essentially a reverse bicycle pump.  It is possible to remove 99.9% of the air molecules and a few more, but that still leaves too many for the cool vacuum electron effects like neon signs, nixie tubes, and for audiophiles, amplifier tubes.

The mechanical vacuum pumps can’t reach those levels; more exotic pumps are needed, but they can get close to where radiometers operate, which is my interest.  So following the advice of expert friends, I acquired a pump that, in principle, could reach the level of vacuum I needed:  50 microns (a micron of mercury air pressure is 1/760 thousandth, call it a millionth, of standard atmosphere).  The pump model I bought is commonly used by the HVAC industry, where air conditioning units need to be evacuated before charging them with refrigeration working fluids (Freon, etc.).  They can reach the 50 micron vacuum level internally, but if you connect it to a real world vacuum chamber, there is a myriad of “leaks” that will prevent getting there.

I found this out by trial and error.  I found that the hoses, fittings, and gauges from the HVAC world were not cheap, but there is a market to keep them reasonably affordable to the industry’s practitioners.  Vacuum-rated hoses, gauges, valves, and fittings (the connectors between vacuum elements that minimize leaks), are hard to make.  And they all seem to have their own connection systems.  I learned about “flare” fittings, “nominal pipe thread” and tapered thread, acme threads, o-rings, and a bunch of other methods for connecting things and trying not to leak air molecules.

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Glass Blowing- Getting the Right Stuff

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The “candles” in a neutral flame from my torch.

I decided that to become more skilled, I would need my own torch and materials so I could practice and make as many mistakes as needed to acquire a specific glass-blowing skill.  I found a torch on eBay, some hoses and fittings on Amazon, a tank of propane from my barbeque grill, but then had to figure out an oxygen source.  I also needed an exhaust system so I wouldn’t asphyxiate while heating glass from my propane-burning torch.

The exhaust system was simple in principle, but of course, the actual implementation was not.  I wanted to create a “glass working station” in a corner of my garage/workshop—a recently built structure with a 10-foot high ceiling with no explicit ventilation.  This has already been a limitation when I wanted to work with paints, adhesives, or solvents that required a ventilated area, so I welcomed the excuse to create a ventilation zone for my shop.

Professional paint and chemistry booths are expensive, so I looked for kitchen exhaust hoods.  I discovered that they have an enormous price range which depends almost entirely on the current popular style and appearance of the sheet metal hood, and almost nothing on the exhaust rate of the fan.  The typical kitchen exhaust rate was less than I wanted anyway, so the fan didn’t matter—I would be replacing it.  I really wished I could buy the exhaust hood sans fan motor, but they are rare.  And when you find them, they cost the same or more.  It’s the external visual style you are paying for. 

I found a low-cost, unattractive but functional, kitchen exhaust hood with a low-power motor that I could replace with one that was more capable.  It seems a huge waste, but these are the tradeoffs in the DIY world.

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Toward a Personal Radiometer

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I was recently struck by an unexplained desire to craft a classic scientific object, a “radiometer”.  It was first created and demonstrated in the 1800s as scientists explored the fundamental elements of nature, especially the behaviors of atoms and molecules.  The periodic table and the ideal gas law that we learned in school were figured out during this time through many careful experiments.

Among the experiments was one performed by William Crookes while trying to isolate and identify his newly discovered element Thallium.  To make high-precision measurements of mass, he avoided the disturbances of air currents on his balance by putting it in a vacuum.  But he found that the readings were still varying, depending on whether the balance was in sunlight or not.  With his laboratory skills, he crafted a device to demonstrate the effect, a device that today is known as a “Crookes radiometer”, or “light mill”.  It is a delicately balanced arrangement of vanes, black on one side, white or silver on the other side, suspended in a glass vacuum tube.  Crookes discovered that when the vanes were illuminated by sunlight, they moved, rotating around the balance point, demonstrating that light induced some force to cause the rotation, and that force was also responsible for the variations in his mass measurements.  See this account for a wonderful history of the radiometer.  There is still some scientific uncertainty about how exactly it works!

My fascination with the Crookes radiometer began as a child when I first saw one spinning in a store window.  My dad was with me and was able to explain it to the satisfaction of his 8-year-old son:  “The light hits the white side and bounces off, but it gets absorbed by the black side and the difference of force makes it move”. 

I immediately set out to make one for myself.  With black and white construction paper I made some vanes and taped them to a pencil.  I found a sunny spot in our backyard and planted the sharp end of the pencil into the ground.  Nothing.  No motion.  It was quite a disappointment. 

When I later explained to Dad that my radiometer didn’t work, he told me that the force of light is very small, and for it to spin required a very delicate balance and removing the air from around the vanes, which was why the radiometer at the store was inside a glass bulb.  It explained why my backyard radiometer had failed, but it didn’t quench my curiosity. 

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Know-How for Whom?

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The QSL postcard sent through the postal service is the mechanism used by ham radio operators to confirm their over-the-air radio contacts. This is my dad’s QSL card for his Idaho station.

As an electrical engineer I learned that “all digital devices comprise analog components”.  This has remained true even as quantum effects are now being utilized in computational logic gates (they are defined by analog wave functions).

Radio waves, especially those used by amateur radio operators, are analog signals transmitted and received by oddly shaped and configured pieces of conducting metal parts known as “antennas”.  And the techniques to couple a useful signal to them are part of the arcane art and science of amateur radio.  The sharing of this knowledge is a big part of the ham radio community ethos. 

So I should not have been surprised to receive an email asking for help with “s-meter calibration” of an antenna.  It was addressed to my dad, who died in 2016, but whose email address has been set to forward everything to me.  I get occasional messages from this account, but with diminishing frequency, and usually from some company or service he had subscribed to, but for which there was no “unsubscribe”.  In this case however, it was from one of his fellow ham radio acquaintances looking for advice.

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