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  1. Plat

    Radiometer rotation speed as function of pressure

    I am experimenting with using a radiometer as an approximate indicator of pressure in my homemade high vacuum system, running a small turbo pump. I am interested in the relationship between pressure and vane rotation speed, with light intensity being constant. I have only been able to find...
  2. Plat

    Turbo pump - vibration and noise at a certain RPM

    I have picked up a used pfeiffer turbomolecular pump and controller for pretty cheap. It runs like a champ, completely smooth and quiet except for when it’s first starting up. As it approaches 5500 rpm, it starts vibrating somewhat and sometimes produces a momentary scraping noise when the...
  3. Plat

    Calculate the strength of several polycarbonate sheets laminated together

    Based on dimensions and the materials' Young's modulus, I know how to calculate the expected deflection of a rectangular sheet of material under a given distributed or point load and given various edge support conditions. I have discovered however that multiple thinner sheets when bonded...
  4. Plat

    Calculate the thickness of a plate to withstand a specified uniform pressure

    In exploring the feasibility of constructing a vacuum chamber, I am trying to calculate the thickness of rectangular polycarbonate sheet needed to withstand 100kPa of pressure, given dimensions of 30.5cm by 61cm (12 by 24 inches) and clamped edges. I have found some calculators that will tell...
  5. Plat

    Properties of RF harmonics

    How can the power/amplitude of a particular RF harmonic be calculated? I would assume it is some well-defined fraction of the amplitude of the main frequency? Do RF harmonics from a square-wave drive appear only on the even, odd, or both, multiples of the base frequency? How do high-frequency...
  6. Plat

    High-frequency transformers - how are they different?

    I apologize for being somewhat scatter-brained here, I just have too many questions on this topic. I know high-frequency transformers use ferrite cores instead of laminated silicon-steel, but what other differences are there? Does their reactance still follow the standard formula: 2*Pi*F*L ...
  7. Plat

    Mains transformer with 1.4 ohm primary winding?

    I don't understand how this is possible. This is a rather large transformer in a stereo system amplifier. The transformer is a simple step-down with 120V mains primary to a center-tapped secondary providing both 38V and 76V. According to ohm's law, at 120V this thing should draw about 85 amps...
  8. Plat

    Low pressure barometer

    I am working on a barometer that will operate t-ed in to an experimental vacuum chamber. The fluid column is composed of vacuum oil so it doesn't boil. I have calculated that given the oil's density of 0.92g/cm3, each cm of oil height indicates 90 pascals of pressure. The oil has a vapor...
  9. Plat

    I Measuring vacuum w/ hot filament - calculation (pirani gauge)

    I am looking for guidance on how to successfully measure vacuum using a device similar to a pirani gauge, my device however is a tungsten filament which is heated electrically to about 90*C, and it's current draw is a measure of vacuum. The problem I am having is how to relate specifically the...
  10. Plat

    Geiger counter and low-energy x-rays

    I have a geiger counter, the specifications say it is sensitive to x-rays down to 30kev. I wonder where that number comes from? Am I correct in thinking that any x-ray photon that enters the geiger tube will register a count, regardless of it's energy? Perhaps the 30kev minimum is there to...
  11. Plat

    Radiation or electrical interference? Geiger counter

    First, I hope this is the correct place for this question. I am experimenting with electrical discharges at low pressure, think plasma globe, and I bought a geiger counter to make sure I am not producing x-rays. My vacuum pump is rated down to 5 pascals. The problem is that the geiger counter...
  12. Plat

    Striations in cathode ray discharge

    What causes these striations? How does the voltage and pressure of the discharge affect the size, color, number, and spacing of the striations? I have produced a discharge with striations with fairly low voltage (under 15kv) and pressure 10 - 100pa, and the striations are very thin, compact, and...
  13. Plat

    X-ray production - maximum pressure

    What is the maximum practical or theoretical pressure at which x-rays can be produced, as in a Crookes tube or cathode ray tube? I know Crookes tubes operate at 0.1pa and lower, but I need to know if I am at risk of producing x-rays with high voltage (60kv+) discharges at medium vacuum, as low...
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