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'[EE] how to obtain cosine'
2006\06\02@083217 by

Hi group,
What would be an easy way to obtain a 90 degrees phase shift
from a transformer output (50/60Hz)
Thanks

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> What would be an easy way to obtain a 90 degrees phase shift
> from a transformer output (50/60Hz)

Pure L or pure C gives this. Not sensibly realisable in most cases.

In practice multiple stages with less shift per stage may be used.

Using active components this can be done very easily.

or you could do it digitally.

Or ...

achieve with what.

RM

>> What would be an easy way to obtain a 90 degrees phase shift
>> from a transformer output (50/60Hz)
>
>
> Pure L or pure C gives this. Not sensibly realisable in most cases.
>
> In practice multiple stages with less shift per stage may be used.
>
> Using active components this can be done very easily.
>
> or you could do it digitally.
>
> Or ...
>
> achieve with what.
>

The pure L or pure C approach would be an integrator or differentiator.
You could have the sine wave drive a capacitor whose other side is
connected to an op amp current to voltage converter (non-inverting input
grounded, feedback from output to inverting input, capacitor connects to
inverting input). The output will be the inverted derivative of the input.
The derivative of a sine wave leads by 90 degrees. When inverted, it
appears to lag by 90 degrees. The differentiator has a 6dB/octave
(20dB/decade) rising frequency response. This can be limited by putting a
small resistor in series with the capacitor (making it not an ideal
differentiator, but will be close at frequencies far below 1/(2*pi*R*C)
where R is the added resistor.

Similarly, integrating a sine wave results in a lag of 90 degrees with a
6dB/octave falling frequency response. You can make an inverting
integrator by grounding the non-inverting input of an op amp, putting a
capacitor between the inverting input and output, then a resistor from the
non-inverting input to your sine source. The integrator "accumulates" the
voltage over time, so any DC offsets (and there will be some) will result
in the integrator ramping towards the rails over time. This can be limited
by putting a resistor across the capacitor, which limits the frequency
response at very low frequencies (like DC). The frequency response of the
integrator approaches infinity as the input frequency approaches zero.
Finally, this is an inverting integrator, so the output lags the input by
90 degrees, but is inverted, so it appears to lead by 90 degrees.

Harold

--
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At 01:32 PM 6/2/2006 +0100, you wrote:
>Hi group,
>What would be an easy way to obtain a 90 degrees phase shift
>from a transformer output (50/60Hz)
>Thanks

At a fixed frequency (eg. 50Hz *or* 60Hz) you could use a simple
RC low pass filter. Or an LC filter, but inductors for such low frequencies
tend to be bulky and expensive. If the frequency varies, the phase shift
and output amplitude will change.

For a wider range, an allpass filter can be used, for example:
http://www.maxim-ic.com/appnotes.cfm/appnote_number/112

Hilbert transformers can be implemented digitally or with analog means,
and can be designed to work over a given frequency range.

If you need high power, as to run a 2-phase motor, the AC can be rectified,
filtered, and converted back to AC to generate what you want. Usually a
2-phase ("split phase") motor uses a simple run capacitor for the phase shift.

I'm really just guessing at your needs, it really depends what you are up to,
but searching on some of terms I've mentioned above should allow you to get
started.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffinterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->>Test equipment, parts OLED displys http://search.ebay.com/_W0QQsassZspeff

Harold Hallikainen wrote:
>>>What would be an easy way to obtain a 90 degrees phase shift
>>>from a transformer output (50/60Hz)
>>

If you have a transformer with a center tapped secondary, (or two
secondaries that can be wired this way), then with one RC network, you
can generate a signal with 0 to 180 degrees of phase shift.

Label the secondary as X = top, Y = center tap and Z = bottom.

Place a resistor from X to a capacitor that then goes to Z. Label the rc
junction as the Output.

Take your signal from Y to the Output.  As the resistor value is
adjusted, the phase *relative to one end of the transformer* will vary
from in phase to 180 degrees out of phase.  Somewhere in the "middle"
will be found the 90 degree point.

With a 3 phase system :
Use a star delta tx this will give you 30 deg shift. Add red and blue this
gives 120 deg shift (120-30=90) ups sensing circuit for control electronics
(1 x lm348) or scott wound transformer for power...

Or rectify then invert (speed controller with mods..)

Steve        ..

-----Original Message-----
From: piclist-bouncesmit.edu [piclist-bouncesmit.edu] On Behalf Of
Dorsey Fahlstedt
Sent: 02 June 2006 13:32
To: piclistmit.edu
Subject: [EE] how to obtain cosine

Hi group,
What would be an easy way to obtain a 90 degrees phase shift
from a transformer output (50/60Hz)
Thanks

Send instant messages to your online friends http://uk.messenger.yahoo.com
At 06:32 AM 6/2/2006, Dorsey Fahlstedt wrote:

>What would be an easy way to obtain a 90 degrees phase shift
>from a transformer output (50/60Hz)

An easy way starts off with a high-voltage AC signal, followed by a
RC low pass filter.  My early dimmers used to do this to get an
almost perfect 90 degree phase shift.

The stuff I did back then was optimized for 120Vac line.  Assuming
neutral is circuit common, 470K resistor from 120Vac input to 100n
film capacitor, other end of capacitor tied to circuit
common.  Adjust value of R so that signal on capacitor is desired
amplitude (12V p-p in the design I did way back then).  Then add
another resistor of equal value from 12V rail to junction of R & C to
shift the bias point to mid-supply.

Simple, easy, very effective.

Note: this was on a design that was completely opto-isolated from any
outside-world terminals that an end-user could touch (line-powered
type of stuff).

dwayne

--
Dwayne Reid   <dwaynerplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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> If you have a transformer with a center tapped secondary, (or two
>  secondaries that can be wired this way), then with one RC network, you
>  can generate a signal with 0 to 180 degrees of phase shift.
>
>  Label the secondary as X = top, Y = center tap and Z = bottom.
>
>  Place a resistor from X to a capacitor that then goes to Z. Label the rc
> junction as the Output.
>
> Take your signal from Y to the  Output.  As the resistor value is
> adjusted, the phase *relative to one  end of the transformer* will vary
> from in phase to 180 degrees out of  phase.  Somewhere in the "middle"
> will be found the 90 degree  point.

Hi, I will try to do this, do you mean that the phase shift will be relative
to Vxz ? or to Vxy ?

p.s.
The reason for my question is that I want to see this circle when connecting
sine and cosine in scope x-y mode, just curious to see it.

Thanks

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On Fri, 2006-06-02 at 20:04 +0100, Dorsey Fahlstedt wrote:
{Quote hidden}

Well, for something like at just using a cap will give you something
close to a circle. Try different caps to see the difference.

TTYL

At 03:21 PM 6/2/2006 -0400, you wrote:
{Quote hidden}

Use a series R and C to ground for X channel and
series C and R to ground for Y channel (you could reverse the two, of course).

Use 27K and a 0.1uF film cap for the R & C in both cases.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffinterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->>Test equipment, parts OLED displys http://search.ebay.com/_W0QQsassZspeff

On Fri, 2 Jun 2006, Dorsey Fahlstedt wrote:

> Hi group,
> What would be an easy way to obtain a 90 degrees phase shift
> from a transformer output (50/60Hz)
> Thanks

A RC group (two R and two C is easiest)

Peter
> If you have a transformer with a center tapped secondary, (or two
>  secondaries that can be wired this way), then with one RC network, you
>  can generate a signal with 0 to 180 degrees of phase shift.
>
>  Label the secondary as X = top, Y = center tap and Z = bottom.
>
>  Place a resistor from X to a capacitor that then goes to Z. Label the rc
> junction as the Output.
>
> Take your signal from Y to the  Output.  As the resistor value is
> adjusted, the phase *relative to one  end of the transformer* will vary
> from in phase to 180 degrees out of  phase.  Somewhere in the "middle"
> will be found the 90 degree  point.
>

Do you have some theory behind this? I would like to understand how
it works before building it.
thanx.

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Dorsey Fahlstedt wrote:
{Quote hidden}

I'm not so great at explaining this stuff but maybe a graphic analysis
will help.  In the attached gif, the bottom line X-Y-Z represents the
center tapped secondary.  VR is the voltage on the resistor, VC is the
voltage on the capacitor and VO is the output voltage.

The phase angle is ALPHA.  As the R and C values change (for a fixed
input frequency), the VO vector will sweep out a 180 degree angle.
THETA represents the phase angle obtained from just the RC components.

If anyone sees a mistake here, please by all means, point it out.

Derivation of the pertinent equations is left as an exercise for the
student.

part 2 4043 bytes content-type:image/gif; (decode)

part 3 35 bytes content-type:text/plain; charset="us-ascii"
(decoded 7bit)

>p.s.
>The reason for my question is that I want to see this circle when connecting
>sine and cosine in scope x-y mode, just curious to see it.

Agree!  That was me, 30 years ago after I got my first 'scope.  And...there
was a magazine article where they took some zener diodes, and clipped the

Barry

{Quote hidden}

I got VO= V * ( JWCR - 1) / ( 1 - W^2 * C^2 * R^2 )

Is this correct?

---------------------------------