Sensitivity of the current probe and oscilloscope combination too low

[Kiriakos GR]

All engineers when it comes down to oscilloscope and current probe combination they are facing identical challenges.

At Current probe age of technology in use, this is responsible for mV/A ratio of output.
At older current probe for Oscilloscope and even for use with a multimeter, 10mV/A at low range 0.2A to 40A this seemed as sufficient for measuring current.

But when you are up to measure AC Phase shift, between voltage and current waveform (50/60 Hz) , one low output 10mV/A current probe, this will deliver a waveform loaded with high noise up to 1/4 of it total measuring range.
Eventually when AC current quantity this increases, the probe now starts to deliver higher voltage output that is in a lesser degree (or percentage) polluted from noise.


Accurate AC Phase shift measurement, this is only possible when both volt and current waveform these are clean from noise pollution.
The oscilloscope will perform AC Phase shift, by calculation of difference in time that its waveform crossing the zero point of sine-wave.     
When current waveform this is loaded with noise, exact point of when this waveform crossing the zero point of sine-wave, this is impossible to me measured.
AC Phase shift measurement this is computed by the oscilloscope, the difference in milliseconds of two incoming waveform when both crossing zero line, this is now computed again and we read a measurement in degree.

Oscilloscope front end noise this seems here of a lesser importance, when the current probe noise this is several decades of mV higher, than actual oscilloscope channel noise level.
For example the worst oscilloscope of our days it might have 1.5 mV as front end noise.

 
Electrical test and measurement industry they are aware of the challenge, sensitivity of the current probe and oscilloscope combination too low, and all their recommendations are in favor of their profitability as always.

Within 2022 they are forth generations of current probe for oscilloscope.
a) Recent made Low-end and low price, these has very high noise, Low measuring accuracy, and in theory are good enough for measurement of current and of nothing else.
b) Twenty years old technology, 1.5% accuracy,  R&D along technology developed at the west world, still not perfect enough for power analysis.
c) Fifteen years old technology, 3.0% accuracy,  R&D along technology developed in Taiwan, there is no demonstration or a public review, this be in favor of this technology superiority.
d) Ten years old technology, HIOKI Japan this did most fresh R&D about high bandwidth and high accuracy and cleaner regarding noise probes, but such a probe solution this include external power supply and retail cost is up to 4000~5000 EUR (for Probe plus PSU Kit).

Speaking of price point vs current probe options available.
a) 100 EUR
b) 600 EUR
c) 450 EUR
d) 4000 ~ 5000 EUR (lowest priced probe).

Several brands of electrical test and measurement sector, they do sale such probes under their own label, and then final retail pricing this gets further inflated.   

Bellow its a photograph this illustrates of how clean it might appear a newer current probe in comparison to an older.
But I do not demonstrate much of faith at this comparison, because Keysight this did not demonstrate actual DUT and electrical application.
But I do agree at 100% that this is the appearance of current waveform loaded with noise VS a cleaner one.

Current waveform full of noise, this occupy a higher portion of oscilloscope time domain scale.
At 230V AC line, one differential voltage probe, this will give output of a much cleaner waveform, zero crossing point it will appear clean and it can be measured with better accuracy.
AC Phase shift measurement this is a dance for two, and therefore one identically clean second waveform it should be there, so zero crossing measurement this be accurate enough.

Electrical theory about manual elimination of factors them causing a challenge at such measurements, this is limited to a single advice.
And this is no other than the use of DIY current coil.
The undocumented expectation, this is current probe output to increase enough and be much more or much higher, than minimum noise introduced by the current probe electronics when this measuring low current with out the use of such a coil.

AC/DC Current coil for measurement and of current quantity multiplication they are usually at 10X, as is most designs of line splitter within plastic housing.   
For a more powerful than 10X coil, the only way this is the DIY path.
FLUKE has one offering of 50X coil, as tool for clamp meter calibration.
 
This period of time, I did decide to become pioneer, and to investigate of how much useful it can be shown the FLUKE 5500A/COIL, at low current boost VS high frequency component attenuation, along of how much cleaner will end to be now the current probe waveform at the screen of my own oscilloscope.

https://www.ittsb.eu/forum/index.php?topic=1766.0   

[Kiriakos GR]

Prior of me getting involved at making my own current coil, I did try to reduce current probe noise, by using available functions at my GDS-2102A Oscilloscope.

First step was of me limiting acquisition bandwidth at 20MHz.
(this did not helped much) screenshot - No1


Second workaround was of me to use 10X coil.
Third workaround was of me limiting acquisition memory of the oscilloscope to Shortest. (screenshot - No2)

After several tests, I was forced to inform GW Instek about my challenge, and ask for an advice.
GDS-2000A series this includes one poorly documented digital filter, this able to do bandwidth filtering at the range of 100 kHz up to 5 MHz.
Due this filter activation, the waveform it did looked cleaner, but still the oscilloscope this was struggling to maintain stable trigger of this signal.

Digital filter functionality this is out of electrician basic education, and so I did my own fresh internet based search / research, and I did discover that by a greater possibility this is  a low-pass Bessel filter  and or Bessel-Thomson and or of what Tektronix this mention as FilterVu Variable Low-pass filtering.
(screenshot - No3)

After the activation and of the third in series of workarounds, waveform it did become much cleaner, but most critical problem this is still there, the oscilloscope does not give a stable Phase Shift measurement, instead they are constantly fluctuating degree values, within the range of -77 degree up to -90 degree.
(screenshot - No4)    

[Kiriakos GR]

FLUKE 5500A/COIL this is a tool with specific electrical properties.

It has bandwidth of 40 Hz to 400Hz.
And so I am expecting from it identical attenuation and of any high frequency component, and I will be more than happy if this actually behave as additional passive low=pass filter too. 

Soon I will be able to prove, of how much helpful this FLUKE 5500A/COIL can be, at boosting my current probe mV/A output far and above of introduced noise by probe electronics and of actual signal noise at Low-current ACA.
While at the same time, there is going to be effective passive attenuation, this removing too a portion of high frequency noise. 

My goal and purpose,  this is helping my CA PAC-12 Oscilloscope probe, this to deliver cleanest possible electrical current waveform, so my GDS-2102A oscilloscope to be helped enough so to deliver stable Phase shift at low current as it does when this measuring of higher current.

https://www.ittsb.eu/forum/index.php?topic=1766.0



N.I. company, this uses better in English text, so to describe current coil benefits.
Current probes generally use one of two technologies. The simplest uses the principle of a transformer, with one winding of the transformer being the measured wire. Since transformers work with only AC voltages and currents, current probes of this type do not measure direct current.
The other type of current probe  uses the principle of the Hall Effect.
The Hall effect produces an electric field in response to a current present in an applied magnetic field. This technique requires the use of an external power supply, but does measure both alternating and direct current (AC and DC).

Since current probes measure the current enclosed by their jaws, several techniques can be used that are unique to the current probe.
If the sensitivity of the probe and oscilloscope combination is too low for a particular measurement to be made, several turns of the current carrying wire can be inserted into the jaws.
The probe will effectively have a larger current to measure (the original current times the number of turns).
Although the current does not require a direct electrical connection, it still removes energy from the circuit under test. Normally, this small amount of energy loss will not disturb the circuit, but can be a factor in some cases.

[overvolt]

I do hope your workaround solution this to succeed !!

This is not a world full of angels, but I was thinking so far that the specific pack of brands (test and measurement) that they carry more decency.

They say that young kids its the future, then they mislead consumers, by giving pointers at the wrong direction.
Webinars and free education this is another joke I suppose.

Originally all  electricians professors are the ones who should become our line of defense.
But they are really inexperienced about electrical applications.
ITTSB was founded so to be a place for smart thinkers so them to connect and share experiences.
But at the end of the day, no one spent significant portion of time so to research enough and find the truth all by him self.
     
 
 

[Kiriakos GR]

I do hope your workaround solution this to succeed !!

This is not a world full of angels, but I was thinking so far that the specific pack of brands (test and measurement) that they carry more decency.

Their decency this were lost in the stock-market exchange, their top priority its their stock holders.

While I am now 53 years old, I do find joy that my brain-cells they are still intact and do the job. 
I am not a crusader, but the readers of this blog they worth to be aware of the truth.

GW Instek told me that I did hit hardware limitation of GDS2000A product design and that this oscilloscope its now old.
They recommend GDS2000E instead ....

I am not a moron at using my own money for such experiments.
My next upgrade will be nothing less than a true fast performing 12-Bit scope (16 bit High-res), 350 MHz of bandwidth and at a reasonable price.
And this is not out yet.
   
Thanks mate!
       

[Andrew-88]

To sum up, original current probe output this is 10mV / 1A, and with this 50x coil this is now 500mV / 1A.

And or 50mV per 100mA of load.
And or 0,5mV per 1mA of load.

Your minimum load (at the other project) this is 135mA = 67.5mV at the oscilloscope channel input (with the new coil).
Your chances to succeed, they have increase, lets hope that now they did increase enough.   

It does makes you wonder of what is actual requirement for GDS-2000A regarding amplitude of input signal which is enough for it so to trigger on it?

[Kiriakos GR]

It does makes you wonder of what is actual requirement for GDS-2000A regarding amplitude of input signal which is enough for it so to trigger on it?

This is the 1.000.000 dollars question for every oscilloscope, when it has active two input channels.

Thanks for the math analysis. 

[overvolt]

This last screenshot it must be with the digital filter on.
Did the trigger issue improve?   

[Kiriakos GR]

This last screenshot it must be with the digital filter on.
Did the trigger issue improve?   

Not as much as I was hope for.

But I did discover that others before me in Japan, they did face this identical challenge.
And there is now open one communication window with them.

Problem description:   
The signal is obscured by noise, and the trigger cannot be
applied in a stable manner, so averaging is unable to function.

I did succeed to help the oscilloscope enough so the averaging this to start to work, before I could only use the digital filter.

[Andrew-88]

While I do not own any digital oscilloscope yet, with so much added information, the problem and the solution its now more obvious.
The oscilloscope along both probe's for voltage & current, other than build quality they should be made by the use of low-noise electronics circuitry.
 
When three tools they must be combined for energy measurement (Real power), the weakest tool in this chain it will destroy the quality of the measurement.

 
 

[overvolt]

I did succeed to help the oscilloscope enough so the averaging this to start to work, before I could only use the digital filter.

Nothing stopping you, so to test also x100 coil.

[Kiriakos GR]

I did succeed to help the oscilloscope enough so the averaging this to start to work, before I could only use the digital filter.

Nothing stopping you, so to test also x100 coil.

This is the plan B.