Oscilloscope help
Gordie Orange, Wed Aug 31 2016, 06:16PMMy wife bought me a Velleman hand held scope and a function generator but im struggling to work out what to do (sorry to all the seasoned pros facepalming right now)
I followed the instructions here http://www.hvtesla.com/tuning.html but all i seem to be getting is noise and no visible peaks when i sweep through the frequency.
Im guessing i haven't set the scope up properly but n idea where to look for destructions.
Any help for an enthusiastic newbie greatly welcome
Re: Oscilloscope help
Sulaiman, Wed Aug 31 2016, 08:33PM
The tuned circuit formed by the primary capacitor and inductor ;
the inductor will be a near short circuit from dc to just below the resonant frequency
the capacitor will be a near short circuit at frequencies above the resonsnt frequency
only at or very near resonance will there be a signal,
the amplitude of the signal across the primary would be the same as from the signal generator
if there were no losses, in practice, look for a smaller signal.
The resonant peak can be very narrow (high 'Q' tuned circuit) and can be easily missed,
sweep the frequency painfully slowly :)
First just feed the sig-gen straight into the 'scope and practice getting a stable display at different frequencies and amplitudes.
Sulaiman, Wed Aug 31 2016, 08:33PM
The tuned circuit formed by the primary capacitor and inductor ;
the inductor will be a near short circuit from dc to just below the resonant frequency
the capacitor will be a near short circuit at frequencies above the resonsnt frequency
only at or very near resonance will there be a signal,
the amplitude of the signal across the primary would be the same as from the signal generator
if there were no losses, in practice, look for a smaller signal.
The resonant peak can be very narrow (high 'Q' tuned circuit) and can be easily missed,
sweep the frequency painfully slowly :)
First just feed the sig-gen straight into the 'scope and practice getting a stable display at different frequencies and amplitudes.
Re: Oscilloscope help
alan sailer, Wed Aug 31 2016, 10:07PM
Learning how to use a o,scope is not an especially intuitive thing. So take your time.
As Sulaiman said try first to just get a signal from your function generator into the scope. Skip the coil for now. If you can't get a good stable sine wave display on the scope directly from the signal generator then you need to work on that.
Triggering the scope is always the most difficult part of using one. I am not familiar with the Velleman scope, however most scopes have several triggering modes and a method of setting the trigger point. Messing with these controls is what you need to work with.
If you have a signal generator/scope set-up that can reliably show a sine wave and are able to sweep the sine wave in frequency then you can move to the tesla coil. I only did the test you are trying to run once and I found the test on the secondary easier to run. As Suliman says the resonance can be very narrow so you do need to change the frequency carefully. If your signal generator doesn't have fine frequency control it is possible that you can tune right through the resonance.
Finally, although this way of tuning a coil looks like it is popular, I didn't find it very helpful. Your results may be different.
Cheers.
alan sailer, Wed Aug 31 2016, 10:07PM
Learning how to use a o,scope is not an especially intuitive thing. So take your time.
As Sulaiman said try first to just get a signal from your function generator into the scope. Skip the coil for now. If you can't get a good stable sine wave display on the scope directly from the signal generator then you need to work on that.
Triggering the scope is always the most difficult part of using one. I am not familiar with the Velleman scope, however most scopes have several triggering modes and a method of setting the trigger point. Messing with these controls is what you need to work with.
If you have a signal generator/scope set-up that can reliably show a sine wave and are able to sweep the sine wave in frequency then you can move to the tesla coil. I only did the test you are trying to run once and I found the test on the secondary easier to run. As Suliman says the resonance can be very narrow so you do need to change the frequency carefully. If your signal generator doesn't have fine frequency control it is possible that you can tune right through the resonance.
Finally, although this way of tuning a coil looks like it is popular, I didn't find it very helpful. Your results may be different.
Cheers.
Re: Oscilloscope help
Gordie Orange, Thu Sept 01 2016, 06:08AM
Thanks for the advice,
I had a play and got a stable sine wave while connected directly to the scope and messed about with frequency and amplitude on the signal generator
Gordie Orange, Thu Sept 01 2016, 06:08AM
Thanks for the advice,
I had a play and got a stable sine wave while connected directly to the scope and messed about with frequency and amplitude on the signal generator
Re: Oscilloscope help
Sulaiman, Thu Sept 01 2016, 12:46PM
I've only built a few small TC but I like to measure my coils at sig-gen levels,
most of the key concetps such as simple resonant circuits, coupled resonant circuits, skin-effect, proximity effect, proximity/arc length de-tuning ....
much easier then measuring a running TC
some things can only be tuned at full power,
but a good understanding of tuning, and what makes a 'good TC can be obtained without frayed nerves :)
with a sig-gen and a 'scope you can investigate
capacitors and inductors both have capacitances, inductances and resistances
the ballance of these properties determine its performance as a component in a circuit.
I think that N.Tesla would have eaten his underpants to have a 'scope and sig-gen.
P.S. once the sig-gen and 'scope are easy to use
(where I work, dozens of engineers with decades of 'scope usage each, NONE of us have familiarised ourselves with all of the features of the 'company scopes')
to sweep for the resonant frequency, increase the sensitivity of the 'scope untill you see noise
as you approach resonance reduce the gain on the 'scope.
P.P.S. before you ask, many members have written about high voltage probes,
research before asking ;)
Sulaiman, Thu Sept 01 2016, 12:46PM
I've only built a few small TC but I like to measure my coils at sig-gen levels,
most of the key concetps such as simple resonant circuits, coupled resonant circuits, skin-effect, proximity effect, proximity/arc length de-tuning ....
much easier then measuring a running TC
some things can only be tuned at full power,
but a good understanding of tuning, and what makes a 'good TC can be obtained without frayed nerves :)
with a sig-gen and a 'scope you can investigate
capacitors and inductors both have capacitances, inductances and resistances
the ballance of these properties determine its performance as a component in a circuit.
I think that N.Tesla would have eaten his underpants to have a 'scope and sig-gen.
P.S. once the sig-gen and 'scope are easy to use
(where I work, dozens of engineers with decades of 'scope usage each, NONE of us have familiarised ourselves with all of the features of the 'company scopes')
to sweep for the resonant frequency, increase the sensitivity of the 'scope untill you see noise
as you approach resonance reduce the gain on the 'scope.
P.P.S. before you ask, many members have written about high voltage probes,
research before asking ;)
Re: Oscilloscope help
Gordie Orange, Thu Sept 01 2016, 06:20PM
Little squeal of joy, slowly swept the signal and found a big rise at 265Khz on the secondary, will try the primary when my daughter is asleep.
Gordie Orange, Thu Sept 01 2016, 06:20PM
Little squeal of joy, slowly swept the signal and found a big rise at 265Khz on the secondary, will try the primary when my daughter is asleep.
Re: Oscilloscope help
Sulaiman, Thu Sept 01 2016, 06:26PM
just a quick one;
put a hand a few cm from the topload and see how far the resonant frequency drops (needs practice)
easier, tune to resonance, watch the 'scope as you move your hands around.
add say 12" of wire to the topload to simulate a spark,
notice the slightly reduced resonant frequency
due to increased capacitance.
P.S. the topload voltage of the resonating secondary
(no primary, just sig-gen earth and bottom-feed the secondary)
is enough to light a neon lamp :)
Sulaiman, Thu Sept 01 2016, 06:26PM
just a quick one;
put a hand a few cm from the topload and see how far the resonant frequency drops (needs practice)
easier, tune to resonance, watch the 'scope as you move your hands around.
add say 12" of wire to the topload to simulate a spark,
notice the slightly reduced resonant frequency
due to increased capacitance.
P.S. the topload voltage of the resonating secondary
(no primary, just sig-gen earth and bottom-feed the secondary)
is enough to light a neon lamp :)
Re: Oscilloscope help
Gordie Orange, Thu Sept 01 2016, 06:42PM
Sorry you've lost me
Gordie Orange, Thu Sept 01 2016, 06:42PM
Sulaiman wrote ...
P.S. the topload voltage of the resonating secondary
(no primary, just sig-gen earth and bottom-feed to secondary)
is enough to light a neon lamp :)
P.S. the topload voltage of the resonating secondary
(no primary, just sig-gen earth and bottom-feed to secondary)
is enough to light a neon lamp :)
Sorry you've lost me
Re: Oscilloscope help
Sulaiman, Thu Sept 01 2016, 06:52PM
if you connect the -/outer/Gnd side of your sig-gen to physical or mains earth,
then connect the +/inner/live sig-gen to the bottom of your TC secondary
the voltage at the top of the secondary is high enough to cause a small neon bulb to glow
one side of neon to earth (your hand will do)
the other side to the top of the secondary.
don't forget, 'earthy' objects near the top cause a drop in resonant frequency.
just a way to 'play', lighting a neon from a sig-gen.
Sulaiman, Thu Sept 01 2016, 06:52PM
if you connect the -/outer/Gnd side of your sig-gen to physical or mains earth,
then connect the +/inner/live sig-gen to the bottom of your TC secondary
the voltage at the top of the secondary is high enough to cause a small neon bulb to glow
one side of neon to earth (your hand will do)
the other side to the top of the secondary.
don't forget, 'earthy' objects near the top cause a drop in resonant frequency.
just a way to 'play', lighting a neon from a sig-gen.
Re: Oscilloscope help
Gordie Orange, Thu Sept 01 2016, 09:26PM
ooooh, I'll give that a go.
Thanks for taking the time to explain it
Gordie Orange, Thu Sept 01 2016, 09:26PM
ooooh, I'll give that a go.
Thanks for taking the time to explain it
Re: Oscilloscope help
Sulaiman, Thu Sept 01 2016, 11:47PM
just realised, my sig-gen was probably 8 Vrms 50 Ohm source impedance,
if your sig-gen is battery powered the signal may be insufficient to light the neon,
probably, maybe.
Sulaiman, Thu Sept 01 2016, 11:47PM
just realised, my sig-gen was probably 8 Vrms 50 Ohm source impedance,
if your sig-gen is battery powered the signal may be insufficient to light the neon,
probably, maybe.
Re: Oscilloscope help
Gordie Orange, Fri Sept 02 2016, 08:09AM
This is the signal generator I have
http://www.ebay.co.uk/itm/131324203754?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
Gordie Orange, Fri Sept 02 2016, 08:09AM
This is the signal generator I have
http://www.ebay.co.uk/itm/131324203754?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
Re: Oscilloscope help
Sulaiman, Fri Sept 02 2016, 12:00PM
nice sig-gen.
should work ok.
just for added interest,
did you realise that your T.C. is resonant in the LW radioband ?... :)
Sulaiman, Fri Sept 02 2016, 12:00PM
nice sig-gen.
should work ok.
just for added interest,
did you realise that your T.C. is resonant in the LW radioband ?... :)
Re: Oscilloscope help
Gordie Orange, Fri Sept 02 2016, 12:07PM
is that a bad thing?
Gordie Orange, Fri Sept 02 2016, 12:07PM
Sulaiman wrote ...
nice sig-gen.
should work ok.
just for added interest,
did you realise that your T.C. is resonant in the LW radioband ?... :)
nice sig-gen.
should work ok.
just for added interest,
did you realise that your T.C. is resonant in the LW radioband ?... :)
is that a bad thing?
Re: Oscilloscope help
Sulaiman, Fri Sept 02 2016, 04:23PM
no, it just means that you could, if you wish, tune a LW receiver to your coil's resonant frequency.
EDIT: any progress ?
Sulaiman, Fri Sept 02 2016, 04:23PM
no, it just means that you could, if you wish, tune a LW receiver to your coil's resonant frequency.
EDIT: any progress ?
Re: Oscilloscope help
Gordie Orange, Fri Sept 23 2016, 09:30PM
I got sparks :) and confusion,
I couldnt get anything with a big toroid(24x6") on a 6" coil swapped for a 4x12" toroid and got some good solid streamers.
When I had the sig gen and scope hooked up to tune the primary I found the point where the signal peaked but still couldnt get a spark from the big toroid.
My transformer is 8k 100mA cap bank is 96.7nF and a rotary gap (sync)
Gordie Orange, Fri Sept 23 2016, 09:30PM
I got sparks :) and confusion,
I couldnt get anything with a big toroid(24x6") on a 6" coil swapped for a 4x12" toroid and got some good solid streamers.
When I had the sig gen and scope hooked up to tune the primary I found the point where the signal peaked but still couldnt get a spark from the big toroid.
My transformer is 8k 100mA cap bank is 96.7nF and a rotary gap (sync)
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