Displaying ripple voltage with a scope?

[Brian]

What is the best way to see the ripple voltage with an oscilloscope?
I want to measure the 16V AC that comes off the wall transformer.
The back of the wall transformer says Input: 120V 60Mhz 16Watt and
output is 16V AC 375mA.

At this output voltage that is being measure 16V AC, is it potentially possible
to fry the scope?

Look again at the wall transformer---- I believe it will say 60 Hz (not 60 Mhz).

 

[Sam Kaan]

What is the best way to see the ripple voltage with an oscilloscope?
I want to measure the 16V AC that comes off the wall transformer.
The back of the wall transformer says Input: 120V 60Mhz 16Watt and
output is 16V AC 375mA.

At this output voltage that is being measure 16V AC, is it potentially possible
to fry the scope?

 

[John Fields]

What is the best way to see the ripple voltage with an oscilloscope?
I want to measure the 16V AC that comes off the wall transformer.
The back of the wall transformer says Input: 120V 60Mhz 16Watt and
output is 16V AC 375mA.

At this output voltage that is being measure 16V AC, is it potentially possible
to fry the scope?

 

[Sam Kaan]

Look again at the wall transformer---- I believe it will say 60 Hz (not 60 Mhz).

U are right, 60Hz (typo.)

 

[Sam Kaan]

Well I have a used Tek 7904 with mainframe up to 500Mhz. But the plugging
I have is 7A13 which I think is good up to 100Mhz.

This is just an exercise only as I have no function generator (getting one
soon) and itching to see what
this thing can do.

just out of curiousity, is it safe (to the scope) to measure the 16V AC
directly What is the proper
way to do this? A probe will have the needle and the little alligator clip
for ground. I can understand
it in a DC circuit, but where do you ground this in a AC voltage source?
Could someone please
give a lowdown on how to set up your scope (probe etc) in order to measure a
16V AC output from
a wall transformer. I just want to see that sine wave going across the
screen for now. Thanks.

 

[Sam Kaan]

No, scopes are generally good to several hundered volts.

No offense, but it seems unusual to both own a scope and ask this kind
of question.

Well I am a hobbyist and very new to this. I decided to own a scope hoping
it will help me learn these stuffs better. I know some stuffs about
electronics but
don't have much experience witha scope. Sorry!

 

[Walter Harley]

Well I am a hobbyist and very new to this. I decided to own a scope hoping
it will help me learn these stuffs better. I know some stuffs about
electronics but
don't have much experience witha scope. Sorry!

Sam, you've been asking a lot of questions lately about this scope... you
really, really should get the manuals for it. The old Tek manuals are very
good about explaining everything from the basic principles of operation of
an oscilloscope, all the way to what the particular scope's specifications
are and even how to calibrate and maintain it.

Trying to learn how to use a scope by asking questions on Usenet is like
trying to learn to drive a semi by asking questions on Usenet, I'm afraid.

 

[Luhan Monat]

What is the best way to see the ripple voltage with an oscilloscope?
I want to measure the 16V AC that comes off the wall transformer.
The back of the wall transformer says Input: 120V 60Mhz 16Watt and
output is 16V AC 375mA.

At this output voltage that is being measure 16V AC, is it potentially possible
to fry the scope?

No, scopes are generally good to several hundered volts.

No offense, but it seems unusual to both own a scope and ask this kind
of question.

 

[Rick]

Well I am a hobbyist and very new to this. I decided to own a scope hoping
it will help me learn these stuffs better. I know some stuffs about
electronics but
don't have much experience witha scope. Sorry!

With the price of analog scopes almost cheaper than a good multimeter, I
think almost everyone can own a scope.

Your 16V transformer will most likely be isolated from the 120V mains in
your house, so you should be able to hook the ground (return) lead from your
probe to one side of the 16V output and hook the probe tip up to the other
side (polarity doesn't matter in this case...pick either lead of the OUTPUT
of the transformer for your ground (return) connection. Note that if you
were to try and measure the sine wave of the 120V(rms) output from the wall
outlet directly, you would need to exercise caution not to connect the
ground lead to either side of the wall plug. You could connect it to the
round hole in a 3 prong outlet if you want, but the scope is going to have a
return to ground through its power cord (assuming it is not some battery
operated thingy). Probably safer to use your little 16V transformer to
isolate you from the mains in any case. Note that you will see a sine wave
with a peak to peak voltage of about 46V or even a bit higher (since the
transformer is unloaded). If you looked directly at the wall voltage you
would see a sine wave that went from about -170V to +170V.

If you can buy or build a function generator, you could have some fun
exploring things like low pass and high pass filters, simple transistor
amplifiers, etc. with just a handfull of parts from even *gulp* Radio Shack.
I would recommend getting a good book on basic electronics, then maybe
getting Win Hill's excellent Art of Electronics. I guess you could start
with AoE, but you may want something a bit gentler.

Be safe, have fun, happy new year.

Rick

 

[John Fields]

Well I have a used Tek 7904 with mainframe up to 500Mhz. But the plugging
I have is 7A13 which I think is good up to 100Mhz.

This is just an exercise only as I have no function generator (getting one
soon) and itching to see what
this thing can do.

just out of curiousity, is it safe (to the scope) to measure the 16V AC
directly What is the proper
way to do this? A probe will have the needle and the little alligator clip
for ground. I can understand
it in a DC circuit, but where do you ground this in a AC voltage source?
Could someone please
give a lowdown on how to set up your scope (probe etc) in order to measure a
16V AC output from
a wall transformer. I just want to see that sine wave going across the
screen for now.

---
Set your horizontal sweep speed to 2ms/division, your vertical amplifier
to 10V/division, your trigger to AUTO, and your trigger source to LINE.
Then, adjust your vertical position control until the trace falls on the
center horizontal line of the display grid and adjust your horizontal
position control until the start of the trace moves to the first
vertical line of the display grid.

Now, if the secondary of the transformer is isolated from the primary,
just hook your scope probe across the secondary. If you're using a 1:1
probe you should see a sine wave displayed with the positive and
negative peaks about 5cm apart and if you rotate the TRIGGER LEVEL and
toggle the SLOPE control you'll be able to make the trace start either
going up or going down at exactly 0 volts.

 

[Rick]

---
Set your horizontal sweep speed to 2ms/division, your vertical amplifier
to 10V/division, your trigger to AUTO, and your trigger source to LINE.
Then, adjust your vertical position control until the trace falls on the
center horizontal line of the display grid and adjust your horizontal
position control until the start of the trace moves to the first
vertical line of the display grid.

Now, if the secondary of the transformer is isolated from the primary,
just hook your scope probe across the secondary. If you're using a 1:1
probe you should see a sine wave displayed with the positive and
negative peaks about 5cm apart and if you rotate the TRIGGER LEVEL and
toggle the SLOPE control you'll be able to make the trace start either
going up or going down at exactly 0 volts.

Excellent description. I might add that the reason you see the sine wave
traverse 5 divisions (50 volts) is because the 16VAC value of the
transformer is probably an RMS voltage (root mean square). The peak value
of ONE HALF of the sine wave is 16VAC * SQRT(2) = roughly 23V. The sine
wave amplitude will travel from -23V to +23V and back to -23V in one period
(which for your 60HZ (not megahertz, lol) will be 1/60 sec = 16.7
milliseconds.

 

[Luhan Monat]

Well I am a hobbyist and very new to this. I decided to own a scope hoping
it will help me learn these stuffs better. I know some stuffs about
electronics but
don't have much experience witha scope. Sorry!

Well, then good for you. A scope may be the best thing to buy first to
learn electronics. It lets you 'see' what is actually going on.

 

[Jim Yanik]

C'mon,John give the guy a break,he's a newbie(or it's a typo).It's a 60
*Hertz* transformer,and since it ouputs AC(alternating voltage)there is no
AC ripple to be measured.It's ALL ac "ripple".All he will see is the peak
to peak(p-p) AC sinewave.(the marked rating is the *RMS* value under some
load)

And Sam,you will not fry your scope measuring the isolated low voltage
side.

 

[OhBrother]

Look again at the wall transformer---- I believe it will say 60 Hz (not 60 Mhz).

Not to take things off in another direction, but I'd like to relate a trick
shown to me by my "elmer" many moons ago (his ham call was W9CSS by the
way).

We had just finished building a power supply and he said "Now, let's measure
the ripple".

He connected an oil-filled capacitor in series with the DC output and set a
VOM on the AC range between it and ground. He then switched the meter into
one of its more sensitive ranges, and read out the small amount of ripple.

I was 16 at the time and was duly impressed. Hopefully someone can make use
of this.

O'

 

[IcePhoenix]

60 Mhz Mains?!? That sounds extremely unusual... I would think that would be
60Hz mains for nearly every standard power transformer, especially if it is
a "wall" transformer... <G>

As far as the "ripple voltage" is concerned, that is a component of
rectified AC, more commonly known as DC...
Rectified voltage usually has a capacitor inline with it to smooth out the
"ripples" between the crests of each sine wave. The larger the capacitor
used, the smoother the "ripple" in the DC voltage. AC voltage is ALL ripple
as it varies from "negative" to "Positive" voltage 60 times per second.

If you are hoping to see how "precise" the voltage is, you can either set
the Volts/Division lower i.e. 2v instead of 5v and adjust the 'centerline'
up or down to see only the peaks or valleys, or you can set the scope to
read the "peak" voltage variance... but that requires a fairly "high end"
(read expensive) scope to accomplish that. <G>

Taranach