Recent content by Plat

  1. Plat

    Radiometer rotation speed as function of pressure

    I have considered using drag to measure pressure as you describe, but I think at pressures as low as I’m working with, drag would be negligible compared to the torque produced by even a small motor. I am interested in measuring in the range of 1Pa to 0.001Pa.
  2. 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...
  3. 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...
  4. Plat

    Calculate the strength of several polycarbonate sheets laminated together

    I have been using simple lacquer thinner to wet the surface of one sheet and then press another against it. My understanding is that this solvent causes the polycarbonate from each piece to fuse together, leaving no foreign material or adhesive. I have done deflection testing with a 20cm beam...
  5. 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...
  6. Plat

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

    The full thickness of the sheet will be comprised of two thinner sheets solvent laminated together. Thus, the chamber will have an inner and outer layer of polycarbonate, with the inner and outer layers alternately overlapping each other at the corners so that the force under pressure is never...
  7. Plat

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

    I agree however I am not an engineer, that's why I'm asking.
  8. 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...
  9. 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...
  10. Plat

    High-frequency transformers - how are they different?

    That's very very helpful, thank you. Are there any inherent/unavoidable losses as frequency increases that cannot be 'tuned' away in the transformer's construction? For example, could a transformer that was properly designed to operate at 200kHz be just as efficient as one that was designed to...
  11. Plat

    High-frequency transformers - how are they different?

    How does the core material affect the frequency it can be used at? Is the advantage of ferrite its lower magnetic permeability? And is this an advantage because it results in lower inductance and therefore lower inductive reactance? I don't know how that could make sense because even with a...
  12. 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 ...
  13. Plat

    Mains transformer with 1.4 ohm primary winding?

    I had no idea inductance played such a big role here. Thank you for the explanation and I'll be committing that equation to memory.
  14. Plat

    Mains transformer with 1.4 ohm primary winding?

    That makes perfect sense but I have measured the primary windings of other mains transformers with the same meter and got reasonable values of around 200 ohms. I wonder why this one is different? Just larger as far as I can tell.
  15. 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...
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