Measuring Phase

[walters]

When measuring phase on the oscilloscope i see 2 waveforms one is leading or laging the other

example 1::

Waveform#1 is 10us laging Waveform#2

What is the phase angle of 10us?

how do i find the phase angle from a time measurement?


Example 2::

Waveform#1 is 40ms ("laging") waveform#2

What is the phase angle of 40ms?

How do i find the phase angle of 40ms?


Example 3::

Waveform#1 is 40ms "Leading" waveform#2

What is the phase angle of 40ms?

How do i find the phase angle of 40ms?

See how the 40ms is the same distance from waveform#1 zero crossing point to waveform#2 zero crossing point but the only difference is the leading and laging this should give a different phase angle even tho it has the same 40ms time difference?

 

[_3iMaJ]

You can't determine phase angle w/o knowing the frequency my friend.

 

[walters]

Do i measure waveform#1 total time measurement? to get the freq?
and measure waveform#2 total time measurement? to get the freq?

Or how do i get the frequency of the time difference between the two waveforms?

 

[akg]

which type of wave form, sine?

 

[walters]

two Sinewaves or two square waves or 2 triangle waves

how do i measure phase from all 3 different forms please?

What would be the difference from the type of waveform it is?


Measuring frequency for a sinewave?
Measuring frequency for a square wave?
Measuring frequency for a triangle wave?

isn't the same just measure the time for 1 cycle or period ?

 

[akg]

two Sinewaves or two square waves or 2 triangle waves

how do i measure phase from all 3 different forms please?

What would be the difference from the type of waveform it is?


Measuring frequency for a sinewave?
Measuring frequency for a square wave?
Measuring frequency for a triangle wave?

isn't the same just measure the time for 1 cycle or period ?

the sine wave is represented by

V(t) = V(max) * Sin(wt + theta)
w = 2*pi*f
t is the time and
theta is the angle
so if u know f,t vmax etc. u can get the phase lag etc

 

[walters]

Thanks for the help

But with the oscilloscope all i can measure is the Time difference the time between the 2 waveforms


Waveform#1 >>>40us>>>Waveform#2

I measured 40us on the oscilloscope so what do i do now?
40us is the time distance between the 2 waveforms

 

[akg]

Thanks for the help

But with the oscilloscope all i can measure is the Time difference the time between the 2 waveforms


Waveform#1 >>>40us>>>Waveform#2

I measured 40us on the oscilloscope so what do i do now?
40us is the time distance between the 2 waveforms

why can't u measure voltage and freq?? , with osc: u shld be able to ..

 

[walters]

So if i measure the frequency of waveform#1 and measure the frequency of waveform#2 where do i go from here

example waveform#1 is 1K
waveform#2 is 700hz

time difference is 40us between waveform#1 and waveform#2

If i know the frequencys of the waveform#1 and #2 and i know
the time difference is 40us what do i do know to get the phase
angle?

How do i know is waveform#1 is laging or leading?

example waveform#1 is 500hz
waveform#2 is 500hz

time difference is 40us between waveform#1 and waveform#2

If i know the frequencys of the waveform#1 and #2 and i know
the time difference is 40us what do i do know to get the phase
angle?

How do i know is waveform#1 is laging or leading?

 

[evandude]

So if i measure the frequency of waveform#1 and measure the frequency of waveform#2 where do i go from here

example waveform#1 is 1K
waveform#2 is 700hz

time difference is 40us between waveform#1 and waveform#2

If i know the frequencys of the waveform#1 and #2 and i know
the time difference is 40us what do i do know to get the phase
angle?

the two waves have to be the same frequency to have a specific phase angle... otherwise the distance between two particular points on the waves, as you would usually measure them with an oscilloscope, such as the zero crossings, will be different every cycle. if you don't see why, try drawing (or graphing with a computer) two sine or square waves with different frequencies and try measuring the time difference at several points.

example waveform#1 is 500hz
waveform#2 is 500hz

time difference is 40us between waveform#1 and waveform#2

If i know the frequencys of the waveform#1 and #2 and i know
the time difference is 40us what do i do know to get the phase
angle?

How do i know is waveform#1 is laging or leading?

the period of the waves is 2 mS. 40 uS is 2% of 2mS, and one cycle of a wave is 360 degrees, the phase difference is 2% of 360 degrees, or 7.2 degrees. basically, it's (t/T)*360, where 't' is the time difference and 'T' is the period of the wave (1/frequency)

you know whether one waveform is leading or lagging the other by looking at the image on the oscilloscope. if a waveform is leading the other, it will appear to be shifted to the left of the other one. that might seem backwards at first glance but think about it a bit and it should make sense.

 

[_3iMaJ]

Just push the "measure phase" button. Thats much easier. Or learn how to do simple math.

 

[walters]

Thanks alot for the information and examples

But how do you convert Time measurements like

40us to degrees?
600ms to degrees?
100us to degrees?
20us to degrees?
70ms to degrees?

Because degrees is like a percentage? of 360degrees?

 

[evandude]

you don't just "convert a time measurement to degrees", at least not just some arbitrary time period by itself... the phase angle only has meaning when you are talking about the time delay between signals with respect to the period of those signals.

the phase is a percent of 360 degrees. the time delay between two signals is a percent of the period of the signals. and the percentages are equal.

(time delay/period)=(phase angle/360 degrees)

measuring on a scope, the time delay can vary between 0 and the period, thus making the phase angle vary between 0 and 360 degrees accordingly.

 

[walters]

Thanks alot evandude for the help

The period=360 degrees?

This is a good formula

(time delay/period)=(phase angle/360 degrees)

now how would i know if its leading or laging?


If the time delay is 40us
the period is 100us

phase angle would be
40us/100us= 0.4 percent? or degrees?

 

[Styx]

Well British Universities charge £1000 per year in Tuition fees (going up) for an electronic degree....


walters, it has already been said phase-shift is only relevant between waveforms of the same freq.


Take a simple sinusoidal waveform


Sin(wt)

That has a freq of w
Now lets take a waveform

Sin(wt + a)

THIS waveform now has a phaseshift of "a" radians w.r.t. Sin(wt).


So say you have two waveforms of the same freq and you measure the time difference between them (say looking for the zero-crossings). you NEED to know the freq.

Say you have a phase shift of 50us (measured from the scope) and the freq is 1kHz.

The period for 1kHz is 1mS. 50uS is 5% of the total time period, so the phase shift in degree's is 5% of 360deg = 18deg


THIS is true for any repeating waveform: Triangle, squarewave, complex
AS LONG AS THE FREQ ARE EQUAL

 

[walters]

Thanks for the help

The period for 1kHz is 1mS. 50uS is 5% of the total time period, so the phase shift in degree's is 5% of 360deg = 18deg

The period is 1ms
Time delay is 50us

is the 18degrees laging or leading?

How do i get the other way around getting 342 degrees? because 18degrees is one way of looking at it laging or leading and 342 degrees in the other way of looking at it lagging or leading

So how would i get the percentage of 342 degrees please?

 

[panic mode]

but what are you really trying to do? see and interpret difference on oscilloscope or build circuit to measure it?

 

[walters]

Measure phase time delays on a oscilloscope im just trying to learn the theory behind measuring time delays leading and lagging percentages

Leading percentages and Laging percentages are different from the same time delay measurement

So i don't know which waveform is leading or laging how do i tell or find out?

 

[walters]

Can someone please correct my degrees and percentages of 360
because im worried thats they are wrong

Period=360degrees
frequency=period
Period= 800ms


40us Time delay Percentage of 360 degrees? is it 18 degrees?
(40us is not the period its the time delay between the waveforms)
so if 800ms is the period what is 40us in percentage to 800ms? is it 5%


600ms Time delay Percentage of 360 degrees? is it 270 degrees?
(600ms is not the period its the time delay between the waveforms)
so if 800ms is the period what is 600ms in percentage to 800ms? is it 75%

100us Time delay Percentage of 360 degrees? is it 45 degrees?
(100us is not the period its the time delay between the waveforms)
so if 800ms is the period what is 100us in percentage to 800ms?

20us Time delay Percentage of 360 degrees? is it 9 degrees?
(20us is not the period its the time delay between the waveforms)
so if 800ms is the period what is 20ms in percentage to 800ms? is it .025%?

70ms Time delay to Percentage of 360 degrees? is it 31.5 degrees?
(70ms is not the period its the time delay between the waveforms)
so if 800ms is the period what is 70ms in percentage to 800ms? is it 12%?

 

[akg]

not
frequency=period

frequency=1/ period ..ok may be a typing error

]
40us Time delay Percentage of 360 degrees? is it 18 degrees?

yes if two waveforms (of same freq) time diff at point is 40us then the hase diff is 18