Wien - Maxwell bridge

Discussion in 'The Projects Forum' started by Teslafan, Oct 3, 2014.

  1. Teslafan

    Thread Starter New Member

    Mar 8, 2011
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    Hi,
    I have a question about bridge circuits. Let's say i have a circuit with unknown load containing nothing but capacitors, inductors and resistors, and i want to calculate the number of each component as a total (total Farad, Henry, Ohms). Can i use a Maxwell bridge to calculate the inductance and then a Wien bridge for the capacitance? I know that the resistance can be calculated using the active power. I also thought of using an LCR meter but i don't know whether is practical to use this in a house for example, to calculate the power factor.
    Any thoughts appreciated.
    Thanks
     
  2. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Depending on the type of bridge. Most lab grade Maxwell bridges have an internal oscillator (normally 1KHz) which allows you to read inductance or capacitance values directly, rather than reactance. They are not generally designed to measure complex impedances (though you can use the dissipation factor reading to measure parasitic resistance or limited amounts of "intentional" resistance)

    An RX bridge (such as General Radio) 1650s/816s, and the like will give you the complex impedance of any combination of inductance, capacitance, and resistance. To figure out component values, you have to work from reactance to inductance or capacitance, howevrer.
     
  3. Teslafan

    Thread Starter New Member

    Mar 8, 2011
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    Thanks for the useful info KL7AJ.
    After reading my project again, it seems that i have to detect the total RLC parameters of a distribution system, using only a low frequency test signal and maybe a custom circuit of my own. I can find resonant frequency and resistance using voltage and active power but now i need a circuit to accurately measure the capacitance or inductance. I thought maybe an LC meter will do the job but with a little motification to measure only one of the two parameters so i can calculate the other one using the resonance frequency formula.
    Any thoughts on that?
     
  4. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Yeah....doing this for low frequencies is a bit trickier. A cheap noise bridge works great for RF up to about 30 MHz or so. What frequency are you looking at?
     
  5. Teslafan

    Thread Starter New Member

    Mar 8, 2011
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    Well i was looking for around 50 Hz so i can adjust it using realistic conditions according to the power distribution system in my country. For low frequencies maybe the best parameter to measure is the capacitance and that is what i am looking for right now..
     
  6. Teslafan

    Thread Starter New Member

    Mar 8, 2011
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    I am looking for around 50-100 Hz. A high pass filter is probably good but i have to give it a shot first.
     
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