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From: "Don" <g@crcomp.net>
Newsgroups: sci.electronics.design
Subject: Re: CoB LED filament analysis
Date: Sun, 26 Apr 2026 19:22:00 -0000 (UTC)
Organization: A noiseless patient Spider
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Arie de Muijnck wrote:
> Don wrote:

<snip>

>> My attempts to appease audience obsession with a series shunt resistor
>> caused me to flip the scope's input impedance to "1M ohm AC" and
>> inadvertently leave it at that incorrect current probe setting.
>> After the scope's set to "1M ohm DC" a flat-line trace appears when
>> the two half-wave rectifiers are "off:"
>>
>>      <https://crcomp.net/ledfilament/curveprobe4.png>
>>
>> If that's what Arie means by "required shunt load resistor," then the
>> original current probe curve also shows a more-or-less flat-line trace:
>>
>>      <https://crcomp.net/ledfilament/curveprobe.png>
>>
>> And the anomaly again indicates capacitive current curve corruption
>> caused by the solderless breadboard.
>
> No, the phaseshift was caused by the current transformer being unloaded.
> The perfect load of a CT is a short (e.g. a transimpedance amplifier).
> The breadboard would not cause a measuremable shift. The scope probe alone is
> more capacitive.

Thank you for your kind, thoughtful followup, Arie. AI adds additional
food for thought:

    There is no publicly available comprehensive teardown video
    or detailed technical internal diagram specifically for the
    Fluke i1000s AC current probe. Because the device is a 
    ruggedized, safety-rated tool designed for industrial 
    environments, it is typically serviced as a sealed unit 
    rather than opened by users.

    ### Internal Architecture Overview

    While a detailed schematic is not publicly provided, the 
    mechanical and electrical construction follows the standard 
    design for a high-quality, passive clamp-on current 
    transformer.

    *   **Split-Core Transformer:** The "jaws" of the clamp 
    contain a laminated magnetic core assembly that pivots. When 
    closed around a conductor, this core forms a closed loop, 
    concentrating the magnetic flux induced by the AC current 
    in the conductor
    
    *   **Secondary Winding:** Wrapped around this core is a
    secondary coil with a high number of turns. This coil converts
    the primary current into a proportional, lower-level current
    signal.
    
    *   **Passive Signal Conditioning:** Inside the probe's handle,
    the secondary signal passes through a network of resistors 
    and potentially capacitors. This passive network provides the 
    selectable output ranges (1 mV/A to 100 mV/A) and includes 
    filtering components to minimize high-frequency noise and 
    ringing, which is crucial for accurately capturing distorted 
    waveforms on an oscilloscope.
    
    *   **Shielding and Construction:** The internal circuitry is 
    housed within a flame-retardant, high-impact plastic enclosure.
    The output is fed through a high-quality coaxial cable, which 
    is shielded to prevent external electromagnetic interference
    (EMI) from corrupting the low-level signal before it reaches 
    the measurement instrument.

It will take me a while to digest it. Here's an excerpt from Fluke's 
user manual:

    Operation

    Use the following procedure to make a measurement:

    1. Connect the i1000s Current Probe to the desired input channel on the
       oscilloscope.
   
    2. On the Current Probe, select the least sensitive range (1 mV/A). See
       Figure 1 for selector switch location.

    3. On your oscilloscope, select an appropriate range. Use a 1:1 probe 
       setting.

    4. Clamp the probe around the conductor to be measured, and observe the
       current waveform on your oscilloscope display.

    5. Calculate the Amps-per-division on your oscilloscope by dividing
       the vertical scale (mV or V per division) by the i1000s switch position
       (1, 10, or 100 mV/A). For example:

       20 mV per division = 20 A per division 1 mV/A

    <https://assets.fluke.com/manuals/i1000s__umeng0100.pdf>
    
In the end, I need to pay more attention to the response curves included 
in Fluke's manual. If I remember correctly, in TROUBLESHOOTING ANALOG 
CIRCUITS Bob Pease said he finds graphs more revealing than mathematical
analysis.

It's time to end my participation in this thread. In closing, I hope 
this Chinese aphorism is correctly displayed:

不诱于誉，不恐于诽，率道而行，端然正己。

Not tempted by praise, not intimidated by criticism; walking the path 
of principle, one remains upright and true to oneself.
    
Danke,

--
73, Don, WD7Q                                             veritas    _|_
                                                          liberabit   |
https://www.qsl.net/wd7q                                  vos         |