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  1. Hesch

    Self-inductance of a toroid with a rectangular cross section

    Yes. Say that the original values are: N = Norg , I = Iorg. In the approximated model the values become: Napp = 1 , Iapp = Iorg * Norg. The reason for this approximation is that the coil is formed like the thread on a screw, which make calculations difficult.
  2. Hesch

    Induced Voltage from a current

    Well, no emf is induced in wire, due to some magneting field is passing through the wire ( except for some Eddy voltages and -currents ). The formula to be used is: E = dΨ/dt , Ψ is the magnetic flux through some loop formed by a wire. A straight wire doesn't form a loop. Now, if you connect...
  3. Hesch

    Calculating current with and without internal resistance

    Of course the currents through two resistors in series will be the same, but this common current will change, when an inner resistance in the battery is inserted.
  4. Hesch

    Calculating current with and without internal resistance

    You have chosen the right circular current path to be clockwise, and that's ok except +48Ileft then becomes -48Ileft. The reason why you have to choose directions ( arrows ) before setting up equations, is that you must respect your chosen directions! Otherwise you will get a wrong result.
  5. Hesch

    Calculating current with and without internal resistance

    Don't use the node law to define directions. Just define. You are free to choose directions. If your choise - as for an arrow direction - turns out to be opposite to the physical positive current direction, the resulting current will just be negative. You can use the KVL law, as you have...
  6. Hesch

    How to calculate voltage drop

    You must choose a current through all the resistors in series. The currents are the same, you know. Let's say you choose 2A, then the resistor values will be: 1. (12V - 8V) / 2A = 2Ω 2. (8V - 6V) / 2A = 1Ω and so on. But other values can be used. Say that you choose a current = 2mA, the...
  7. Hesch

    I Extracting sinusoids from FFT

    You can do a lot with these transforms. Say you have a sattelite photo of a milititary airport and you want to know how many jet fighters of which type is parked in this airport, you can employ a lot of people with magnifying glasses to count these planes. But also you could stuff the photo...
  8. Hesch

    I Extracting sinusoids from FFT

    Well, I have recently done some experiments, transforming some shapes like the letters 'E' and 'F'. Then I calculate the transfer function from 'F' to 'E': FFT(H) = FFT('E') / FFT('F'). Now, if I transform the letter 'O' and calculate: IFFT( FFT('O') * FFT(H) ), will I get a 'Q' ??
  9. Hesch

    I Extracting sinusoids from FFT

    A FFT will give you a complex value for each harmonic in your set of discrete data points. Say that the FFT value of the 4. harmonic is ( 0.3 + 0.5i ), you may interprete it as 0.3*cos(4ωt) + 0.5*sin(4ωt) . . . if I understand you correct.
  10. Hesch

    Engineering DC motor differential equation

    Ka and Kb have the same value, but the units are [Nm/A] and [Vs] respectively. There are people that can prove it.
  11. Hesch

    Engineering DC motor differential equation

    Ok, then use these types as input/output. Setting La = 0, you will get a 2. order transfer function.
  12. Hesch

    Engineering DC motor differential equation

    Of course the input and output type matters. If you change the type of input or output, the motors behaviour will change. In the model, choosing ω(s) as output, the transfer function will be H(s). Choosing θ(s) as output, the transfer function will be H(s)/s: θ(s) = ω(s)/s.
  13. Hesch

    Engineering DC motor differential equation

    Well, the transfer function is a differential equation. Using Laplace transform it may be written: H(s) = output(s)/input(s) When expressing the transfer function by its Laplace transform, it becomes much easier to calculate at controller. I have some questions: - Is it a DC-motor ? - What...
  14. Hesch

    What magnetic position sensor to choose?

    Well, yes, but a line imager only sees a line. Say that there is a disturbance in the image, e.g. an unwanted reflection near the edge of the ball and on that line, the line imager will be completely confused: The position of the ball will not be measured correct. In a spatial image most of...
  15. Hesch

    What magnetic position sensor to choose?

    The idea of using a camera will work, but there are some things to be considered: - The images must be of good quality ( e.g. white ball, black background, good illumination ). - The image must be at least 1000 x 1000 pixels - The lens will distort the image ( lens distortion ) so that the...
  16. Hesch

    Capacitors in earthed circuits

    If you have to change the voltages across a capacitor, you must have current flowing through this capacitor. If just one switch is open, no current can pass through the serial connection. Remember Kirchhoffs current law ( KCL ).
  17. Hesch

    Capacitors in earthed circuits

    The capacitors are coupled in series. All the switches must be closed before the charges can get away ( rearrange ). None of the suggestions have all switches closed, so D) is correct because the voltages V1, V2 are unchanged ( no change in the location of the charges ). Don't bother about the...
  18. Hesch

    Find the transfer function for this signal flow graph

    I think the man is called Mason, and sorry: I think you are your method is wrong. Now, if you number the points from x to y: 1 . . 6, the transfer function from 1 to 2 seems to be 1. But later you will have a problem with the W4 from 1 to 3. You must move this W4 connection from 1-3 to 1-2. You...
  19. Hesch

    What could be the ratings of inductor used?

    I recommend a core with an actual airgap. The inductance depends on the amount of magnetic energy in the core, created at some current. This energy is proportional to H*B. If you sketch a B(H) hysterisis curve as for the magnetic material, the magnetic losses in the core will be proportional to...
  20. Hesch

    What could be the ratings of inductor used?

    The burning of L1 may be due to: 1) Too big conductive losses in the coil. 2) Too big magnetic ( hysteresis ) losses in the core. In case of 2), use another core with an airgap, thereby reducing the magnetic losses. Most of the variation of magnetic energy in the core will take place in the...
  21. Hesch

    Measuring a DC motor's inductance

    Why do you want to measure? What's the purpose? Say you going to make a digital controller for this motor. Having measured L and R, you will have to z-transform a transfer function, taking calculation time delay in the controller into consideration, and so on. If that's the case, there is...
  22. Hesch

    Second order system

    The equation 2s2 + 4s + 8 = 0 has two complex roots: s = -1 ± j√3. If the characteristic equation were to have a damping ratio = 1, it should have two real roots at the same location, for example. s1 = -1.2 , s2 = -1.2. In this case the characteristic equation could be written: s2 + 2.4s +...
  23. Hesch

    Second order system

    ( 2s2 + 4s + 8 ) * y(s) = 8 * x(s) Finding y(s)/x(s) the characteristic equation of the transfer function will be: 2s2 + 4s + 8 = 0 → s2 + 2s + 4 = 0 which can be formulated s2 + 2ξωns + ωn2 = 0 So ωn = 2 , the damping coefficient, ξ = 0.5
  24. Hesch

    Engineering Finding Phase Difference in an RC circuit

    Ii = Io = Vi/(R - j/ωC) Vo = Io * ( -j/ωC ) Phase shift = Φ , where Φ is calculated from Vo/Vi = xxxx∠Φ ( result in polar notation ) You may find an easier way, but this is the "basic" method.
  25. Hesch

    Control systems: Simplifying block diagram

    To determine the steady state gain from the above equation, let s → 0, so h(0) = H(0) * Kp * Kb / ( 4 + Kp )
  26. Hesch

    Control systems: Simplifying block diagram

    You don't need to show in this form. Using Mason you should get: h(s)/H(s) = Kp * Kb / ( 2s + 4 + Kp ) → h(s) = H(s) * Kp * Kb / ( 2s + 4 + Kp ) ( if you wish )
  27. Hesch

    Control systems: Simplifying block diagram

    Figure 1 shows two closed loops: An inner and an outer loop. Use Mason's rule to calculate the transfer function as for the inner loop. Insert this inner transfer function in the outer loop and use Mason again to calculate h(s)/H(s) for the outer loop ( the transfer function for the outer...
  28. Hesch

    Magnetic flux and current directions of transformer

    Read Faradays law again: dΨn/dt does not induce a current, but a voltage. Say that the secondary winding is unloaded, no current at all will pass the secondary winding.
  29. Hesch

    I Angle between two vectors with many dimensions

    Yes, but: The DFT coefficients of all harmonic frequecies gives the differences in phases, one signal to another. Think of a Bode plot where the phase varies as a function of frequency. Likewise the phases of different harmonics in a DFT ( or FFT ) depend on the order of the harmonic.
  30. Hesch

    I Angle between two vectors with many dimensions

    Say you do a Fast Fourier Transform (FFT) at some signal, some complex coefficient to some harmonic could be: 3 + j4. This means that this harmonic has a phase referred to the Fourier interval = θ. Tan(θ) = 4/3 → θ ≈ 53°. The absolute value of the coefficient = 5, so this coefficient could...
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