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  • Users: DHambley
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  1. DHambley

    Residential structures - Code enforcement in Northwest Arkansas?

    Preface: I'm a retired PE from WA State, building a home in Benton County Arkansas. We found a builder who has built many homes in this area. I liked him as he personally performs all the tile and trim carpentry - really nice work. We picked a floor plan (I have no time nor desire to design...
  2. DHambley

    PC board anchoring for Aircraft Vibration

    I have a small, approx 1.25" x 2.5" PC board (called a daughter board) which I need to connect to a larger board. In our box there is only enough room to either, 1. Attached the smaller board at a 90d angle to the mother board with a 90d connector or, 2. Bolt the daughter board several inches...
  3. DHambley

    Case grounding requirement of electronic equipment in composite aircraft.

    Every circuit I have ever designed for aircraft requires the case to be grounded to aircraft frame, or a braided cable tied to a nearby structure, or a grounding pin on the connector. EMI test labs I have worked with routinely check for a 2.5 mill Ohm resistance from case to the test table. In...
  4. DHambley

    Rule of thumb equations for convective cooling of metal surfaces.

    As an electronics engineer I have limited knowledge of heat-flow equations and theory. However, on every new design I need to get a rough estimation of the thermal resistance of a metal to air boundary so I can at least know the temperature rise to within a 10C to 15C accuracy. This analysis...
  5. DHambley

    about MIL-STD-1796 . Have you seen it? Opinions?

    MIL-STD-1796 claims to be the new standard for aircraft, military and other mil-aerospace industries. Has anyone here had a chance to review it? Does it address modern electronic parts? (not interpolation on reliability of tubes) Many of us know the deficiencies of MIL-STD-217 and others (for...
  6. DHambley

    There once was a PhD . . .

    No, not "from Nantucket". New job - The guy I replaced was a Phd; really, really good at mathematics of control theory. His software algorithm covered every parameter of the motor and system, from details of the Lq & Ld inductances to the mechanical damping of the load on the shaft. Sharp guy...
  7. DHambley

    IGBT mimum on-time requirement

    Does anyone have any explanation showing why there is a minimum on-time of an IGBT? My colleague said we need to have a minimum because he heard it long ago. All I found on a google search is an app note from Semikron saying that the effect of turning off an IGBT when it is still turning on is...
  8. DHambley

    equation for E field due to current in loop (near-field)

    I need to model our present system to show a predicted before-and-after E-field noise in our attempt to meet FCC part 47 class-A (industrial location). We're not spending the money for EMI lab time until we have a prototype EMI fix. I'm looking for a generalized equation to predict the E-field...
  9. DHambley

    equation for E-field due to current loop

    I have an EMI problem to solve. Our 3-ph motor cables have a sawtooth waveform of ~80A pk-pk at 20kHz and ~300V pk-pk square wave (ignoring the low frequency sinusoidal component). The motor is 2m from the driver, with the three cables ~2m long and 5cm spacing each (three side by side). This...
  10. DHambley

    Connectors for board to wire harness in a sealed box

    Does anyone have suggestions for the type/brand of connectors which are made to withstand the vibration and heat seen in an automotive environment? The connectors and wire harness join several PC boards within a sealed and enclosed box within the engine compartment so, dirt and water are not a...
  11. DHambley

    How much trial-and-error at your work location?

    I'm just curious as to the prevalence of trial and error in different industries. Below, I describe two situations with two different design methods. It may be sucessfully argued either way that one is better than the other. Method 1: Try a 1/4 inch shaft on the new conveyor belt design. Put...
  12. DHambley

    How can I get MathCAD to show flux density in units of Guass

    I typed in the equation for flux density using cm^2 for the core area and the other units are Volts, Turns and time. I expect mathCAD to give my answer in either Tesla or Guass. The answer which it gives is 10^4 times what it should be (if the answer were in Guass) but it doesn't give units...
  13. DHambley

    multipliation rule for independent variables

    We have an issue with our customer concerning the stack-up of tolerances. Its similar to the common multipliation rule for independent variables for reliability calculations but this concerns the stack up of tolerances. I am looking for a MIL-standard paragaph which calls out the proper way to...
  14. DHambley

    Ridley model with complex loads

    Does anyone have any experience working with the Ridley model for a current mode control PWM with complex loads? My load is a mixture of resistors, diodes, caps and inductances. The CMC-PWM spice model for my circuit using a simple block with a modulator gain instead of the Ridley model works...
  15. DHambley

    Space Shuttle Endevour launch delays - electronic box failures.

    About the "electronic box failures" which are preventing the space shuttle launch - There should be NO failures of any system for Christs sake! We spend so much tax money for engineering firms to "prove" that every system is ultra-reliable for aerospace, so these continual failures are...
  16. DHambley

    Fire on 787 during test. Any thoughts on cause?

    On Tuesday 11/09 the cabin of 787 #2 filled with smoke and flames were seen in an aft EE bay. Some instrument displays in the cockpit went out and some flight controls. The RAT system deployed. Would anyone want to guess at the cause before Boeing tells the public?
  17. DHambley

    Orcad PSpice help - plot axis in dB uA

    As many of the Orcad users may have noticed, the Orcad/PSpice forums are getting less helpful over the years. Maybe someone here knows the solution... I'm analyzing an EMI filter using the FFT function in PSpice. (The FFT is done after a transient, not an AC sweep). I use the "add trace"...
  18. DHambley

    current-sense resistor for space with a rated pulse power

    Most of us know that a resistor can take very high pulse power if the pulse width is much less than the thermal time constant. My problem is, if the thermal time-constant isn't specified or tested, or if there's no chart of pulse power vs time, we can't use it. (per our customers reliability...
  19. DHambley

    current-sense resistor pulse rating

    I would like to know if anyone knows of a Hi-Reli current sense resistor with test data of continuous pulse ratings. Several of our circuits have pulses in the 100's of KHz range, way beyond the thermal time constant. The average power is 100mW but the power during an individual pulse of a few...
  20. DHambley

    friction stir welding - wing skin

    Is FSW possible for the wing skin on large (like 747) aircraft. The stress on the lower skin during deflection testing must be concentrated on discontinuities such as rivet points. I would think the overall thickness of the skin could be reduced if these weak points weren't there, saving tons of...

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