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2024-04-19, 22:55:55
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Author Topic: Investigating "anomalies" in Bifilar coils  (Read 201337 times)
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img  picowatt
Re: Investigating "anomalies" in Bifilar coils « Reply #250 on: 2017-05-03, 20:01:11 »
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Greetings all...

Well, I must say this is all a bit intriguing to say the least.  If I can clear up my schedule a bit, i may have a go at a replication.

Might I suggest that those replicators that are using an FG with a known output impedance, such as 50R, measure the FG's open circuit voltage and compare that to the FG's output when connected to the circuit.  The difference between those two numbers divided by the 50R output Z will give you another Pin number to compare to the Pin calculated using R2 (or R2A).  Although it does not rule out the possibility of phase shift within the FG's 50R, it will give you a another Pin for comparison. 

TK, when measuring across R2A where you say you observed a phase shift, was The FG out, R2A, and the CH1 probe point in close proximity (i.e., limited wiring inductance)?

Also, if one were to use a 1/4 watt 1% (or .1%) low TC MF resistors at the output and another identical resistor in series with the FG out and the L1 input, at some of the power levels observed (particularly with TK's FG), the Trise of those small wattage resistors should make Pin/Pout comparisons a bit more obvious to the touch (or a thermister/Tsensor).

Only somewhat tongue in cheek, and with a bit of a grin, it should even be possible to do a "which resistor smokes first" test using 1/8 watt resistors (or even 0805's or smaller).  Just watch the TC (and inductance) of the resistors used. 

Just a few quick thoughts...

PW   
« Last Edit: 2017-05-03, 22:13:36 by picowatt »
   
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Re: Investigating "anomalies" in Bifilar coils « Reply #251 on: 2017-05-03, 20:08:56 »
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Quote from: Vasik041 on 2017-05-03, 17:48:27
Hi Partzman,

Could you please confirm - how you feeding power into the coils ?
Do you take any special measures to match impedance or just connect to signal generator ?

I think this is important part of circuit (power source) left without much attention.

Thanks,
Vasik

PS I also don't understand why not use setup like this ? (attached)

Vasik,

I apologize as I previously missed this post until now.  I have already answered your input question so I'll respond to your question regarding the sense resistor location.  With the optional position you show, the signal level across the sense resistor is low enough to create some difficulty in making accurate differential measurements with a scope.  The only reason to use this location as compared to the grounded connection I show, would be to include any current drawn from the generator as a result of coupling from the DUT to any nearby grounded object, probe cable shield, etc, that would otherwise not be seen by the grounded sense resistor.

Tests have shown this to be negligible.

Edit:  See my post #138 for results of this testing.

Pm     
   
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Re: Investigating "anomalies" in Bifilar coils « Reply #252 on: 2017-05-03, 20:26:23 »

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The rectangular wire that Gyula suggested using
Quote
1kg 3.15mm x 1.12mm
Is it worth trying this wire, if so i can order a couple of reels.

How are you guys determining the turns required in your coils?
   
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Re: Investigating "anomalies" in Bifilar coils « Reply #253 on: 2017-05-03, 20:30:42 »
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All,

For anyone trying to replicate the MEI device, I would recommend you do a simple test when the device is in operation: Move the scope probe cables one at a time to see if your measurements are affected in any way to see if they are acting as antennas at your operating frequency.  You might want to reduce your sample averaging to 4 if it is higher so there is little delay in response.

I would also recommend a scope re-calibration after a suitable warmup just prior to taking measurements.  Perhaps even several times a day if you are on the bench that long.

Pm
   
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Re: Investigating "anomalies" in Bifilar coils « Reply #254 on: 2017-05-03, 20:39:29 »
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Quote from: partzman on 2017-05-03, 20:08:56
Vasik,

I apologize as I previously missed this post until now.  I have already answered your input question so I'll respond to your question regarding the sense resistor location.  With the optional position you show, the signal level across the sense resistor is low enough to create some difficulty in making accurate differential measurements with a scope.  The only reason to use this location as compared to the grounded connection I show, would be to include any current drawn from the generator as a result of coupling from the DUT to any nearby grounded object, probe cable shield, etc, that would otherwise not be seen by the grounded sense resistor.

Tests have shown this to be negligible.

Edit:  See my post #138 for results of this testing.

Pm   

Partzman,

Thank you for clarification.
from your post #138

Quote
When using these correction factors in my original example, the corrected input voltage of 6.492v rms = 6.487 and the corrected input current of 30.53ma = 31.84ma for a corrected Pin = .207*cosine(-81.8 degrees) = 29.46mw.  The original uncorrected and calculated Pin = (6.492*.03053)*cosine(-81.8 degrees) = 28.27mw for comparison.  The corrected COP = 43.7mw/29.46mw = 1.48.

Not corrected COP = 43.7 / 28.27 = 1.54, so difference is 6%, not so small.

It would be easier make measurements on lower frequencies, if you have ferrite rod from MW radio you can try placing it into middle of the coils (just an idea)

Regards,
Vasik
   
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Re: Investigating "anomalies" in Bifilar coils « Reply #255 on: 2017-05-03, 20:40:14 »
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Quote from: Peterae on 2017-05-03, 20:26:23
The rectangular wire that Gyula suggested using Is it worth trying this wire, if so i can order a couple of reels.

How are you guys determining the turns required in your coils?

Peterae,

IMO there is no need to go to any expense at this point with the wire although I'm sure it would work.  The results are achievable with magnet wire and ribbon cable whether wound as individual coils or as a Tesla bifilar pancake coil. 

Using two wires from a ribbon cable wound on a form (other than round) with 25-50 turns should give you a workable device.  More turns increases both the inductance and distributed capacitance which means the operating frequency range will be lower and perhaps more manageable.

Pm
   
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Re: Investigating "anomalies" in Bifilar coils « Reply #256 on: 2017-05-03, 20:51:30 »

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Quote
Peterae,

IMO there is no need to go to any expense at this point with the wire although I'm sure it would work.  The results are achievable with magnet wire and ribbon cable whether wound as individual coils or as a Tesla bifilar pancake coil.

Using two wires from a ribbon cable wound on a form (other than round) with 25-50 turns should give you a workable device.  More turns increases both the inductance and distributed capacitance which means the operating frequency range will be lower and perhaps more manageable.

Pm
Thanks partzman, i will give it a try.
   
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Re: Investigating "anomalies" in Bifilar coils « Reply #257 on: 2017-05-03, 21:01:44 »
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Quote from: Vasik041 on 2017-05-03, 20:39:29
Partzman,

Thank you for clarification.
from your post #138

Not corrected COP = 43.7 / 28.27 = 1.54, so difference is 6%, not so small.

That is true and I agree.  We are assuming that this change is due to slight displacement and induction currents which may or may not be the case.  Prudent shielding would be in order to determine for sure.

Quote
It would be easier make measurements on lower frequencies, if you have ferrite rod from MW radio you can try placing it into middle of the coils (just an idea)

I agree that lower frequencies would better but my experience has shown that as the frequency is lowered by purposeful coil design, the the COP<1.  When one adds adds a ferrite core in the center of the coil arrangement as you suggest, there is no change on the circuit measurements or parameters as one would expect.  These are clues to the device's operation and no, I do not have the answers  :-[!

Pm

Quote
Regards,
Vasik
   
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Re: Investigating "anomalies" in Bifilar coils « Reply #258 on: 2017-05-03, 22:11:01 »

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Leads shortend where possible yields a slightly higher COP @ 1MHz (1.22 instead of 1.2).

Linking my both identical TBP coils together (both equiped with a 51 Ohm load resistor and 1 Ohm csr) drops the output of the first to half while input stays the same.
COP now way below 1 (@ 1MHz)

Input of 2th TBP coil was from top of 51 Ohm load resistor of 1st TBP coil (CH3 purple probe point), ground of 2th TBP coil was via its 1 Ohm csr to the common ground point.

I also tried Picowatts suggestion for an alternative Pin method, but that did not match up (using Vrms values). FG open circuit value 7.127V, when connected to circuit 5.082V.
Difference is  2.045V, divided by 50 gives 40.9mW while the measured input power was 147mW


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Re: Investigating "anomalies" in Bifilar coils « Reply #259 on: 2017-05-03, 22:21:31 »
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Hi guys,

I tested partzman's bifilar coil as per TK's circuit below.

I do get OU from 450kHz to 2.7MHz with all probes set to 1x. However, if I change the input voltage probe (only) to 10x the OU is mostly gone as demonstrated in video.
The higher the frequency (450kHz and above) the more the output. However, the input  goes up as well as I raise the frequency. Haven't took the time to find the ideal frequency.

Link to video demo: https://www.youtube.com/watch?v=B0V18JAafhc

The signal generator is a 20MHz BK Precision with output at max.
The BPC is 16 turns (each coil) of  0.9mm wire with 0.07 Ohms DC resistance per coil.
The Inductance is 16uH and the capacitance is 1500pf
The load and current sensing resistors are selected (tested) precision metal film resistors.

The video is kind of long and I had to cut off the end as the camera created a second file and it wasn't worth the time to edit them together. It should be good enough to get the idea of what it does.

Luc
« Last Edit: 2017-05-04, 01:00:01 by gotoluc »
   
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Re: Investigating "anomalies" in Bifilar coils « Reply #260 on: 2017-05-03, 23:25:41 »
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Hi Graham,

I believe the ebay offer http://www.ebay.co.uk/itm/10m-Professional-Quality-Pure-Copper-OFC-4-x-1mm-Blue-Bi-Wire-Loud-Speaker-Cable-/332043613736?hash=item4d4f577628:g:73IAAOSwImRYOCxf you linked to targets mainly Hi-Fi 'maniacs', featuring the 4x1mm loudspeaker cable consisting of high spec 99.99% oxigen free, multistrand (4x89) copper wires... 
I would also think if this cable is indeed professionally designed, then the electrical capacitance between the 4 insulated strands is relatively low but perhaps this may be now a 'feature' for you because you are forced to choose the operating frequency from 1 MHz and higher onwards as you have written.
(In my earlier practice when helped a friend building RF power amplifiers decades ago, he needed low impedance transmission lines to build wideband matching transformers, hence the need was to use either tightly twisted thick enamelled wires or parallel guided copper foils (stripes) with very thin insulating layer between them to get high electrical capacitance as a result. This is why I suggested the enamelled strips with rectangular cross section.)   
And if you go through Partzman's recent post (#255) on the cables he suggested to Peter, then very likely the above loud speaker cable could also be used, their presumably low self capacitance between any 2 of the 4 isolated strands would not be a drawback for you.  However, the measuring process above 1 MHz will need much closer attention.

Gyula

Quote from: Grumage on 2017-05-03, 15:33:08
Dear Gyula.

Many thanks for your reply.

I was suggesting that pure Copper cable as a quadfilar arrangement, as PM seems to have used what we call " bell wire " over here, you call it " hookup wire " ?

Slightly changing the subject what's needed to wind a coil that can resonate in the 10/100 of kHz range? I would like to join in but my gear is out of puff at 1 MHz.

Kind regards, Graham.
   
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Re: Investigating "anomalies" in Bifilar coils « Reply #261 on: 2017-05-03, 23:34:08 »
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Quote from: gotoluc on 2017-05-03, 22:21:31
Hi guys,

I tested partzman's bifilar coil as per TK's circuit below.

I do get OU from 450kHz to 2.7MHz with all probes set to 1x. However, if I change the input voltage probe (only) to 10x the OU is mostly gone as demonstrated in video.
The higher the frequency (450kHz and above) the more the output. However, the input  goes up as well as I raise the frequency. Haven't took the time to find the ideal frequency.

Link to video demo: https://www.youtube.com/watch?v=B0V18JAafhc

The signal generator is a 20MHz BK Precision with output at max.
The BPC is 16 turns (each coil) of  0.9mm wire with 0.07 Ohms DC resistance per coil.
The Inductance is 16mH and the capacitance is 1500pf
The load and current sensing resistors are selected (tested) precision metal film resistors.

The video is kind of long and I had to cut off the end as the camera created a second file and it wasn't worth the time to edit them together. It should be good enough to get the idea of what it does.

Luc

Luc,

Thanks for running the tests and making the video.  I did look at the P2220 probe specifications and the capacitance is 17pf and 110pf for the 10X and 1X positions respectively.  I do have two suggestions for you if you don't mind.  First, I would like to see the results if all three probes are run at 10X to compare with the 1X and the 10X/1X mix results.  My reasoning here is that there may be possible cable shield ground effects occurring between CH2,3 and CH1 at these frequencies.  Just a thot!

Secondly, I seemed to notice odd variations in the Math output power channel as you are slowly sweeping the signal generator from time 5:25 to 5:50 in the video.  This could be a result of the scope's math calculations trying to keep up but it could also be from the full screen measurement of incomplete numbers of cycles.  I would like to see the results if you tuned to a full number of cycles on screen rather than a specific output voltage level for comparison.

Again thanks for the effort.

Pm
   
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Re: Investigating "anomalies" in Bifilar coils « Reply #262 on: 2017-05-04, 00:06:33 »
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Quote from: gotoluc on 2017-05-03, 22:21:31
Hi guys,

I tested partzman's bifilar coil as per TK's circuit below.

I do get OU from 450kHz to 2.7MHz with all probes set to 1x. However, if I change the input voltage probe (only) to 10x the OU is mostly gone as demonstrated in video.
The higher the frequency (450kHz and above) the more the output. However, the input  goes up as well as I raise the frequency. Haven't took the time to find the ideal frequency.

Link to video demo: https://www.youtube.com/watch?v=B0V18JAafhc

The signal generator is a 20MHz BK Precision with output at max.
The BPC is 16 turns (each coil) of  0.9mm wire with 0.07 Ohms DC resistance per coil.
The Inductance is 16mH and the capacitance is 1500pf
The load and current sensing resistors are selected (tested) precision metal film resistors.

The video is kind of long and I had to cut off the end as the camera created a second file and it wasn't worth the time to edit them together. It should be good enough to get the idea of what it does.

Luc

How in the world do you get such high inductance with only 16+16 turns in that small coil? I have far more turns in my coils and my inductances are in the 600-700 microHenry range. You say 16 milliHenry for a small coreless coil with 32 turns? Are you quite certain of that?

Also, it would be very helpful if you could have your scope show the Phase Angle between CH1 and CH2, because that would allow manual calculation to check the scope's Math result.

Vrms (CH1) x Irms (CH2) x cos(Phase Angle 1-->2) = average input power

The fact that you need to use 1x probes is a huge red flag, because your probes are becoming part of the circuit at that level of no attenuation. 

Is your Function Generator's Black output lead isolated from ground? Many such FGs have their BNC shields connected to chassis ground and back through the mains line cord to the ground pin, and hence to all other instruments that are on the same mains circuit. This may cause complications that need to be taken into account when probing various parts of the circuit.

When I changed from metalfilm resistors and long wiring like yours to non-inductive resistors and minimal wiring length it became harder to get "OU" results at low frequencies.

   
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Re: Investigating "anomalies" in Bifilar coils « Reply #263 on: 2017-05-04, 00:12:07 »
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Quote from: partzman on 2017-05-03, 21:01:44
That is true and I agree.  We are assuming that this change is due to slight displacement and induction currents which may or may not be the case.  Prudent shielding would be in order to determine for sure.

I agree that lower frequencies would better but my experience has shown that as the frequency is lowered by purposeful coil design, the the COP<1.  When one adds adds a ferrite core in the center of the coil arrangement as you suggest, there is no change on the circuit measurements or parameters as one would expect.  These are clues to the device's operation and no, I do not have the answers  :-[!

Pm

The way to add a "core" to a flat pancake coil is to put it on a flat plate of core material like iron or a ferrite slab,  not stick something through the center.
   
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Re: Investigating "anomalies" in Bifilar coils « Reply #264 on: 2017-05-04, 00:17:23 »
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Quote from: partzman on 2017-05-03, 20:30:42
All,

For anyone trying to replicate the MEI device, I would recommend you do a simple test when the device is in operation: Move the scope probe cables one at a time to see if your measurements are affected in any way to see if they are acting as antennas at your operating frequency.  You might want to reduce your sample averaging to 4 if it is higher so there is little delay in response.

I would also recommend a scope re-calibration after a suitable warmup just prior to taking measurements.  Perhaps even several times a day if you are on the bench that long.

Pm

Yes, the probes will act as antennae. Yes, scope self-calibration is important but the effects we are seeing are so strong that slight inaccuracies due to ambient temperature changes affecting calibration are not so significant. Some scopes, like my z-box, take a long time to complete their self-cal routines (up to 19 minutes for mine) so it is probably better just to work in a temperature-controlled environment rather than re-calibrating the scope several times a day. Other scopes take much less time, apparently, so YMMV as usual.
   
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Re: Investigating "anomalies" in Bifilar coils « Reply #265 on: 2017-05-04, 00:27:07 »
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Quote from: picowatt on 2017-05-03, 20:01:11
Greetings all...

Well, I must say this is all a bit intriguing to say the least.  If I can clear up my schedule a bit, i may have a go at a replication.

Might I suggest that those replicators that are using an FG with a known output impedance, such as 50R, measure the FG's open circuit voltage and compare that to the FG's output when connected to the circuit.  The difference between those two numbers divided by the 50R output Z will give you another Pin number to compare to the Pin calculated using R2 (or R2A).  Although it does not rule out the possibility of phase shift within the FG's 50R, it will give you a another Pin for comparison. 

TK, when measuring across R2A where you say you observed a phase shift, was The FG out, R2A, and the CH1 probe point in close proximity (i.e., limited wiring inductance)?

Also, if one were to use a 1/4 watt 1% (or .1%) low TC MF resistors at the output and another identical resistor in series with the FG out and the L1 input, at some of the power levels observed (particularly with TK's FG), the Trise of those small wattage resistors should make Pin/Pout comparisons a bit more obvious to the touch (or a thermister/Tsensor).

Only somewhat tongue in cheek, and with a bit of a grin, it should even be possible to do a "which resistor smokes first" test using 1/8 watt resistors (or even 0805's or smaller).  Just watch the TC (and inductance) of the resistors used. 

Just a few quick thoughts...

PW
Yes, the slight phase shift observed when trying to do the CH1-CH4 differential measurement across R2b was due to wiring inductance, and I was able to reduce it (but not eliminate it) with more careful probe and reference lead placement.  Let us please be sure we are talking about the same thing here.... the CH1 probe point is connected to R2b, not R2a, and the R2a phase shift CH1-->CH2 is an entirely different matter and does not require a differential measurement. But yes, the FG Black output lead and CH2 reference are connected very closely to one side of the R2a resistor and the CH2 probe is connected right at the other side of this resistor.  See the closeup of my connections posted earlier in the thread. (But note that I now am using non-inductive load resistors, 4ea. 4.7 ohm 1% in TO-220 packages for R1, connected in series with as short leads as possible.) And yes, the CH1 probe and CH4 probe are connected directly against the body of the R2b resistor when trying to do the differential measurement across this resistor (which strategy I have now abandoned as being irrelevant and hard to do properly.)

However all problems trying to read the Vdrop across R2b are eliminated simply by removing all probes and their reference clips from the circuit and measuring at R2a and R2b with the same probe and reference lead sequentially. (Obviously requires an isolated FG so as not to create a groundloop.) Doing this shows that the currents flowing in R2a and R2b are identical in amplitude (see scopeshot below comparing a stored reference Vdrop trace from R2a with a live trace from R2b.)
   
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Re: Investigating "anomalies" in Bifilar coils « Reply #266 on: 2017-05-04, 00:55:41 »
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Quote from: TinselKoala on 2017-05-04, 00:06:33
How in the world do you get such high inductance with only 16+16 turns in that small coil? I have far more turns in my coils and my inductances are in the 600-700 microHenry range. You say 16 milliHenry for a small coreless coil with 32 turns? Are you quite certain of that?

Sorry, my mistake it's 16uH and not 16mH. I've corrected it in my post. Thanks for pointing it out.

Quote from: TinselKoala on 2017-05-04, 00:06:33
Also, it would be very helpful if you could have your scope show the Phase Angle between CH1 and CH2, because that would allow manual calculation to check the scope's Math result.

Vrms (CH1) x Irms (CH2) x cos(Phase Angle 1-->2) = average input power

If the scope (TDS 2024B) has this feature, I've never used or seen it in the menus. Sorry

Quote from: TinselKoala on 2017-05-04, 00:06:33
The fact that you need to use 1x probes is a huge red flag, because your probes are becoming part of the circuit at that level of no attenuation. 

Good to know, thanks

Quote from: TinselKoala on 2017-05-04, 00:06:33
Is your Function Generator's Black output lead isolated from ground? Many such FGs have their BNC shields connected to chassis ground and back through the mains line cord to the ground pin, and hence to all other instruments that are on the same mains circuit. This may cause complications that need to be taken into account when probing various parts of the circuit.

My FG is on a 1/1 Isolation transformer. I also checked it with a battery powered inverter just to make sure the results are the same which they are.
The scope is also on its own (separate) 1/1 Isolation transformer.

Quote from: TinselKoala on 2017-05-04, 00:06:33
When I changed from metalfilm resistors and long wiring like yours to non-inductive resistors and minimal wiring length it became harder to get "OU" results at low frequencies.

This was a quick attempt to see the effect. From here mods like a shorter FG cable can be tested.

Thanks for your input

Luc
   
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Re: Investigating "anomalies" in Bifilar coils « Reply #267 on: 2017-05-04, 01:24:28 »
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OK, Luc, thanks for making all that clear, especially the inductance value!   ;)


I've had a look at the User Manual for your scope and you are right, I don't see any obvious easy way to display Phase Angle between two signals. You can still do it manually using cursors and some external calculations but it is definitely a pain. I'm surprised that this scope doesn't seem to be able to do it automatically.
   
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Re: Investigating "anomalies" in Bifilar coils « Reply #268 on: 2017-05-04, 01:26:04 »
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Just for reference purposes here is a closeup of my coil connections. I am no longer using the R2b resistor as I have demonstrated to my satisfaction that the current measured here is the same as the current measured by R2a.
   
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Re: Investigating "anomalies" in Bifilar coils « Reply #269 on: 2017-05-04, 01:57:04 »
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Would this test method be of any value? It allows current sensing in the primary ground leg and should eliminate the normal heavy ground loop of the SG.

 A suitable wideband isolation transformer for L3, L4 can be made on a small ferrite core, have very few turns at these frequencies and can be designed to have very low coupling capacitance.

We don't have to care about the losses in the wideband isolation transformer because we are measuring on the output of this transformer which is measured input to the DUT. A well designed transformer will adequately reflect the generator impedance or turns ratio can be adjusted to provide a proper impedance match to the DUT (which Vasik suggested could be useful).

 It allows sensing input current on the input side, ground referenced, and allows noting coupling capacitance and power leakage to ground through the TBF on the output side sense resistor or that resistor can be eliminated so that you can make a possibly more accurate measurement of output power on the right hand side, as well as accurate input power on the left.

IOW R2 and probe 4 are not really needed with this method. The bottom of the winding on the right can go directly to ground. (ver2)

All scope probes can be star grounded at the schematic ground point.

I'm sure partzman (or someone) has probably tried this and I missed it. If of no value, disregard.

Regards
« Last Edit: 2017-05-04, 03:33:34 by ION »


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Re: Investigating "anomalies" in Bifilar coils « Reply #270 on: 2017-05-04, 03:26:22 »
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Quote from: TinselKoala on 2017-05-04, 00:27:07
Yes, the slight phase shift observed when trying to do the CH1-CH4 differential measurement across R2b was due to wiring inductance, and I was able to reduce it (but not eliminate it) with more careful probe and reference lead placement.  Let us please be sure we are talking about the same thing here.... the CH1 probe point is connected to R2b, not R2a, and the R2a phase shift CH1-->CH2 is an entirely different matter and does not require a differential measurement. But yes, the FG Black output lead and CH2 reference are connected very closely to one side of the R2a resistor and the CH2 probe is connected right at the other side of this resistor.  See the closeup of my connections posted earlier in the thread. (But note that I now am using non-inductive load resistors, 4ea. 4.7 ohm 1% in TO-220 packages for R1, connected in series with as short leads as possible.) And yes, the CH1 probe and CH4 probe are connected directly against the body of the R2b resistor when trying to do the differential measurement across this resistor (which strategy I have now abandoned as being irrelevant and hard to do properly.)

However all problems trying to read the Vdrop across R2b are eliminated simply by removing all probes and their reference clips from the circuit and measuring at R2a and R2b with the same probe and reference lead sequentially. (Obviously requires an isolated FG so as not to create a groundloop.) Doing this shows that the currents flowing in R2a and R2b are identical in amplitude (see scopeshot below comparing a stored reference Vdrop trace from R2a with a live trace from R2b.)

TK,

Sorry for the R2a/R2b confusion.  I thought R2 remained just plain old R2 and that the added CVR at the FG out was referred to as R2a.  But yes, I was discussing R2b, the CVR at the FG out.

However, I am now confused as to why you are disconnecting all other probes when measuring the Vdrop across R2b.  What "problems" are eliminated by disconnecting the other probes?


PW
   
img  picowatt
Re: Investigating "anomalies" in Bifilar coils « Reply #271 on: 2017-05-04, 04:15:33 »
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I have a quick thought on all the "isolating" of FG's and 'scopes some are doing.  For example, Tinman is apparently using a battery/inverter on his 'scope, and Luc is using an iso xfmr on his FG.  Even TK's FG with its switch selectable isolation likely applies as well.

For all these methods used for isolation, they should be considered more so as merely "cap coupling" the signal and chassis ground.  The value of the "coupling cap", or leakage, will be determined by many factors, mostly related to physical placement of the isolating mechanism, or winding capacitance in the power supplies or iso xfmr used.  The coupling capacitance may be very small, but I would want to attempt to quantify that value.

One might consider placing a 10K or so resistor across a 'scope probe and its ground lead.  Set the FG to a known amplitude and frequency somewhere in the neighborhood of those used in these OU tests.  With all other probes and FG cables disconnected, touching the 'scope probe tip/resistor lead wire to the FG's output center pin should produce no signal at the 'scope if the FG and 'scope are truly isolated.

However, if you do see signal from the FG, which you likely will, the coupling or leakage capacitance can be calculated based on the voltage drop measured, the 10K resistive load at the probe, and the frequency of the signal at the FG.

PW

My apologies, I keep hitting "quote" instead of "modify"...  Is there any way to completely delete posts here?
   
img  TinselKoala
Re: Investigating "anomalies" in Bifilar coils « Reply #272 on: 2017-05-04, 08:44:34 »
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Quote from: picowatt on 2017-05-04, 03:26:22
TK,

Sorry for the R2a/R2b confusion.  I thought R2 remained just plain old R2 and that the added CVR at the FG out was referred to as R2a.  But yes, I was discussing R2b, the CVR at the FG out.

However, I am now confused as to why you are disconnecting all other probes when measuring the Vdrop across R2b.  What "problems" are eliminated by disconnecting the other probes?


PW

Since my oscilloscope does not have isolated channel references (like Russ Grier's TDS2024b does), it is necessary to disconnect all the probe reference leads in order not to create a groundloop when measuring across the two resistors separately.  So to measure the current through R2a, I connect the probe tip close to one side of the resistor and the probe reference to the other side. Then I move the probe and its reference to either side of the R2b resistor. If some other probe reference remains connected to the "ground" side of R2a, the common ground point, then this point is shorted to the side of the R2B resistor which has its probe reference connected. 

My FG's "black" output (bnc shield) can be isolated by a switch. It is pretty neat the way the F43 achieves this; its metal box is grounded to the mains cord ground pin, but the circuit board is isolated and all the BNC connectors (it has 5 on the front panel) are insulated bulkhead feedthrus. The circuit board is only grounded to the case at a single point and this point is connected through the switch (which is normally on the back panel but I have relocated it to the front panel for convenience.) Of course as soon as one connects a BNC patch cord from the F43 to another, grounded, instrument this isolation goes away, but in this case I have not done that.
 
My ElCheepo DDSFG is powered by a 2-pin 5 VDC wallwart power supply so its outputs are also isolated from the mains ground, unless patched to another grounded instrument.

You are of course correct in that this results in some capacitive coupling to true Earth ground, but this doesn't seem to be a problem with measurements of this circuit. The important feature of the "isolation" is that the Black (bnc shield) FG lead is not directly connected to the mains cord ground pin and thus to the chassis ground and probe ground references of the oscilloscope or other mains-powered and grounded instruments.


To completely delete or "remove" a post.... click on the "remove" button next to the "quote" and "modify" buttons at lower right.
   
img  Vasik041
Re: Investigating "anomalies" in Bifilar coils « Reply #273 on: 2017-05-04, 09:45:38 »
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Quote from: TinselKoala on 2017-05-04, 08:44:34
To completely delete or "remove" a post.... click on the "remove" button next to the "quote" and "modify" buttons at lower right.

There is no such button  :-\
   
img  Itsu
Re: Investigating "anomalies" in Bifilar coils « Reply #274 on: 2017-05-04, 10:06:47 »

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There is no such button  :-\


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