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East Tester ET4410 ESR Measure

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mawyatt:

--- Quote from: Martin72 on July 31, 2022, 06:42:04 pm ---ET4410:
The signal output stage to H-Cur got a push-pull stage, the output resistance is switchable from 100Ohms to 30Ohms, maximum output voltage is 2Vrms.
Pic shows the actual state of my attempt to draw the circuit, according to the keysight handbook, it´s a auto-balancing bridge.

--- End quote ---

If you trace the Low Cur terminal on the PCB, you'll probably find another Buffered type amplifier with all the selectable resistors shown or the right. With a 30 ohm output and 2 volt signal the max DUT current is 67ma, that's a lot of current for a small Op-Amp to handle without some aid!!

Best,

Martin72:
Actually can´t find it in the manual, but there is a "overload" warning I´ve already reached sometimes.. 8)

mawyatt:
Noted a few things in the schematic you've shown. First off there is a simple technique we've used for decades to "assist" with cross-over distortion in buffered outputs. The 200 ohm resistor R210 from the op-amp output to the buffered output serves to supply current during the cross-over around the zero point where the Slew Rate is the highest and the buffer devices may have trouble keeping up since they are lightly biased there. As the signal increases the Slew Rate slows some and output transistors begin to take the current load away from the op-amp and after 4~5ma the op-amp maxes out. If implemented properly this works very well.

Another couple points, it appears the meter is utilizing the +-5V supply as somewhat references since the signal waveform seems to be coming from the controller and would be a 0 to 5V pulse train to create the signal sine wave and the multipole filter is to filter out everything and leave a nice clean sine wave. The result from the filter will be a unipolar sine wave and this is offset to swing about zero by using the -5V and a resistor R215 (also R205) into the summing node op amp configuration. Using the controller to create a PWM pulse train eliminates the need for a sine wave generator DDS & DAC. Nothing wrong with this approach as it saves some $ in the BOM, but doesn't possess the precision of a typical lab type instrument, but doesn't cost as much either, so very cost effective!! Think todays linear regulator chips are much more stable than those from long ago, know the ones we've utilized were pretty stable and almost spot on the desired output voltage.

Best,

The Electrician:

--- Quote from: Martin72 on July 31, 2022, 07:49:18 pm ---Yepp,
Not so bad for a cheap one.
Test a panasonic FM electrolyt cap, 1000µF/25V on 100khz a few minutes ago.
ESR 0.034 Ohm
D 0.128
Xc -0.267  Ohm
Q 7.81
Phase - 82.7°
And cap....5.95µF  ;)

--- End quote ---

Which meter did you use to make this measurement?  Something's wrong with these numbers.  The phase can't be anywhere near -90 degrees for a 1000uF electrolytic at 100 kHz.  Would you please do this over.  Also show the numbers at 100 Hz for comparison, and measure a few caps larger than 1000uF at 100 kHz please.

mawyatt:

--- Quote from: Martin72 on July 31, 2022, 09:43:13 pm ---Actually can´t find it in the manual, but there is a "overload" warning I´ve already reached sometimes.. 8)

--- End quote ---

Now get yourself a DIY DC Bias Fixture and see just how bad some of the ceramic caps vary with DC bias, also check out the Mylar film types, and electrolytic, then you're nice Mica and Polystyrene types!! Then try some semiconductor diodes to see how they behave with DC bias, fun stuff indeed!!

Oh, and don't forget the DIY Isolation Transformer for Bode Plots of Open Loop parameters with your superb SDS HD DSO :-+

Edit: And forgot, put that nice Twin T notch Filter that you have in the feedback loop of an op-amp, makes nice narrow bandpass filter. Get a high Q inductor and measure it along with your high Q Mica caps, then create a Peltz oscillator!! Fun stuff ahead  ;D

Best,

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