Measure the phase difference between the current and voltage

[KamalS]

To begin with, I want to measure the phase difference between the current and voltage of a signal having a freq. between 10Hz to 100Khz ( I would not mind measuring the same for freq. going up to 1Mhz, if possible using simple "junk box" type components )

To give an idea about my "junk box", I do have a few 74HC4046, XTALs, PICs ( 16F and 18F ).

What I don't have are >30Mhz PLLs, CPLDs, prescalers etc.

1. How do I go about extracting the voltage and current "parts" of a signal?

My end target would be to measure L and C, separately, without worrying too much about their Q ( which you have to take into account when using the LC oscillator type meters )

2. Would the phase difference, caused due to the L/C, between the current and voltage "parts" be, in any way, dependent on the Q of the L/C?

3. From what I saw on the internet, I can carry out some good simualtions to test my queries in LTSpice - but I am just starting to learn it.
Would anyone mind setting up a quick simulation for me guiding me how to extract the V and I and measure the phase difference between them?

 

[srizbf]

Re: Measure the phase difference between the current and vol

no info on the 10khz to 100khz waveform.
sine or square ?

 

[KamalS]

Re: Measure the phase difference between the current and vol

no info on the 10khz to 100khz waveform.
sine or square ?

Good question.

The answer is - I am not sure, but it needs to be whatever will give a more "accurate" result.

You see - I will be using a uC to generate the waveform - hence it would be a square wave.

However, if need be, I would need to make a ( 6th order? ) lowpass filter with notch just below the second odd harmonic of the square wave in question.

If I can come to the same result using a squarewave as a sine wave I could not be happier ( although all the books I have read do the phasor analysis using sinewaves as there is only one freq. to worry about. I reckon analysis using a square wave would bring in more complications? )

 

[srizbf]

Re: Measure the phase difference between the current and vol

if the intention is to measure L/C then sinewave application is the best one.

 

[KamalS]

All right.

So back to the original question ( first post ) with the added detail that the signal is ~5Vpp, sinewave.

 

[srizbf]

Re: Measure the phase difference between the current and vol

apply the sinwave in DUT. measure the voltage with precision rectifier and ADC.
measure the current with a current sense resistor with the same method for voltage.

 

[FvM]

For a today's single chip solution of vector impedance measurement you may want to review the data sheets of the AD5933 and AD5934 devices. They represent a fully digital for the said problem, including the signal generation. In contrast, there are many options for more or less analog circuits.

Regarding your initial questions, an impedance measurement of reactive components always implies complex quantities, in so far "Q" is implicitely playing a role.

 

[KamalS]

Re: Measure the phase difference between the current and vol

For a today's single chip solution of vector impedance measurement you may want to review the data sheets of the AD5933 and AD5934 devices. They represent a fully digital for the said problem, including the signal generation. In contrast, there are many options for more or less analog circuits.

These are indeed interesting!

How much do these cost in low ( 1 - 5 pc ) quantities?

Regarding your initial questions, an impedance measurement of reactive components always implies complex quantities, in so far "Q" is implicitely playing a role.

Could you give me some equations to look at?

Added after 9 minutes:

apply the sinwave in DUT. measure the voltage with precision rectifier and ADC.
measure the current with a current sense resistor with the same method for voltage.

Could you provide some basic schematics?