LCR meter to get the phase angle?

Discussion in 'General Electronics Chat' started by relicmarks, Nov 7, 2008.

  1. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    When using a LCR meter

    Can you measure a RC network or a LC network or LR network?

    Because my LCR meter just only lets me measure them one component at a time , i can't measure the network

    The only way i can get the phase angle is using a dual trace oscilloscope when its a RC,LC,LR or LCR networks. Channel#1 on the input of the LCR network and than the channel#2 on the output.

    Is there a way of using a LCR meter to get the phase angle ?
     
  2. The Electrician

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    Oct 9, 2007
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    What kind of LCR meter is it (manufacturer and model number)?
     
  3. relicmarks

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    A cheap handheld TENMA

    I don't think it can measure NETWORKS or RC, LC, LR, LCR

    I have to disconnect the network and measure them individually one by one

    Plus i have to either calculate the phase angle
     
  4. The Electrician

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    In order to measure phase angle with an LCR meter, it has to be the type that doesn't just measure the inductance or capacitance. It must also measure the Q of the inductor, or the D(issipation) factor of a capacitor. If your meter can only measure the inductance or capacitance, but not the loss, of a component, then it can't measure the phase angle.
     
  5. relicmarks

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    measure the Q of the inductor, or the D(issipation) factor of a capacitor.

    How would u get the phase angle from the Dissipation factor? or Q of the inductor?
     
  6. The Electrician

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    A real inductor has resistance as well as reactance; it is modeled as an ideal inductor in series with a resistor.

    The Q of an inductor at a frequency of w (omega) = 2*pi*f is given by Q= w*L/R, where R is the resistive component of the inductor's impedance. At low frequencies with an air core, the R value is close to what you can measure with DC; this is what an ordinary ohmmeter will measure. At higher frequencies the effective AC resistance will increase due to things like skin effect.

    If the inductor has a ferromagnetic core, the effective R may not be the same as the DC resistance.

    At any rate, the Q of the inductor at any particular frequency is the ratio of the reactance (w*L) to the resistance. Knowing the frequency and the Q, you can calculate the phase angle of the impedance.

    The same thing can be done if you know the D of a capacitor at a particular frequency; see:

    http://en.wikipedia.org/wiki/Dissipation_factor
     
  7. relicmarks

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    Inductors dissipation is a oscillation?

    Capacitors Dissipation is a oscillation?

    Dissipation is a loss of energy in a capacitor and inductor

    Dissipation is a frequency?
     
  8. The Electrician

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    The losses in a capacitor or inductor vary with frequency. Dissipation is not an oscillation in either inductors or capacitors, and dissipation is not a frequency.

    When you measure the dissipation, which is just another word for loss, you must make the measurement at some frequency, which may include the zero frequency, DC. The losses usually vary with frequency.

    Looking back at your original post, perhaps you want to measure phase angle in a circuit where the resistance is a deliberately included component.

    If you have a resistor and inductor in series, that combination can be measured by a suitable LCR meter, and the combination will have a measured Q, from which phase angle of the combination can be determined. Similarly with a resistor/capacitor combination.

    If you have all three components, a resistor/inductor/capacitor, the meter will measure the resultant reactance and indicate it as an effective capacitance or inductance, along with an effective Q or D.
     
  9. relicmarks

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    The losses in a capacitor or inductor vary with frequency.

    Losses of what? frequencys losses? or amplitude losses? or storage losses?
     
  10. relicmarks

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    why would i measure the filter capacitors for dissipation?

    Does High dissipation mean its a short?
     
  11. The Electrician

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    Loss of energy. Sometimes referred to as a power loss in electronic circuits.

    Your questions make me think that perhaps electronics is not your main field of knowledge.

    Do you know why a resistor gets hot when an electric current passes through it?
     
  12. relicmarks

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    1.) Do you know why a resistor gets hot when an electric current passes through it?

    dissipating heat

    2.) Loss of energy. Sometimes referred to as a power loss in electronic circuits.

    Why would a electronic tech care about loss of energy or power loss in a capacitor or inductor ?

    It seems like this loss of energy or power loss is not the same as "leakage"

    To me dissipation is like a weak storage

    But mostly to measure dissipation is to run alot of current though the component to dissipate heat
     
  13. The Electrician

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    You asked in post #1, "Is there a way of using a LCR meter to get the phase angle ?"

    Why do you want to measure phase angle?
     
  14. Wendy

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    Do you just want the phase angle? Or are you after more? A simple exclusive OR gate will put out a measurement of phase angle in the form of a DC voltage if the output is filtered.

    Reactive loss isn't disappated as heat. This is why it is preferred in circuit like flourescent bulbs for current limiting, it has the side benifit of increasing the efficiency a lot.
     
  15. relicmarks

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    Reactive loss isn't disappated as heat

    What does this dissipation LOSS do ? does it change the phase angle?

    I'm not sure what this reactive loss is or does
     
  16. relicmarks

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    The loss factor usually is defined as ratio of resistance to reactance (in series equivalent circuit), thus mathematically it's the tangent of a loss phase angle.


    1.) So if i have a low dissipation the phase angle would be different than a High dissipation phase angle?

    2.) "loss phase angle" means the the amplitude or magnitude of the phase angle has decreased or increased from the dissipation value?
     
  17. Wendy

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    Reactive loss isn't really a loss, not in the same way as resistors are. Due to the phase shift it prevents flow of current, and a convenient way of calculating that is in equivalent ohms, but ohms don't really have anything to do with it. They are a mathematical analog for thinking about these circuits. The more reactance, the more phase shift, and visa versa.

    The catch is phase shift can do some other odd things. As long as you understand the circuit this is no big deal. If you want to see one of the oddities try calculating the voltage across each component on a series LC circuit at resonance, it is quite impressive.

    So why are you wanting to measure phase shift? Like I said earlier, it is easy to build a circuit that will do it, I've never seen the need before.
     
    Last edited: Nov 9, 2008
  18. relicmarks

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    The more reactance, the more phase shift

    1.) Why is that more reactance the more the phase shift?

    2.) a lossy inductor has low reactance and low phase shift?

    3.) a lossy capacitor has low reactance and low phase shift?
     
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