Measurement errors with x10 probe on large negative signals

[Arnoldus]

Hello,
I just tried an other (easier) way to fix the problem, and used an OMRON G3VM61B1 solid state relais instead of an LDR.
It has a FET and is only 2 ohm when ON, the LED needs only 3mA and the switch is bidirectional!
I put the output side (FET) in series with the input of the opamp pin 12, just like the LDR,
and switch the LED with the SENSEL3 signal directly via an FDV303N FET, and a resistor of 1K2 in series from +5V
I cut the little track on the other side of the board, coming from pin12 to R1/R2, and put the opto coupler on the via next to U1,
as can be seen on the picture. The result is an accurate reading and waveform, see picture.

[MatNieuw]

Hi Arnoldus,

I initially looked at a solid state relay (SSR) too (see initial post, a Panasonic AQV216S). But I had two concerns with that:
- What happens to low millivolt signals?
- The Panasonic has a 45 pF capacitance between I/O when off. At 200 kHz and worth the high input impedance of the TL084, maybe you still see an incorrect waveform.
Could you test with a 50 Hz signal of one division peak-to-peak high, and see if it is the same on the low channel (with the OMRON G3VM61B in the signal path), and the high channel?
The same at 200 kHz (I suspect it will be the same as 50 Hz).
Also, if you have the possibility, test with a 200 kHz high voltage and x10 probe, where without the SSR there was distortion, and see if it still is OK? The Omron has 30 pF between I/O.

Finally, I think the scope can withstand more than 50V on the input because the opamps go into conduction but the input attenuator circuits limit the current. But if the scope is in high voltage mode and the SSR is off, the Omron can withstand 60 V. What happens if that is accidentally exceeded? For this reason I looked at the AQV216S which can handle 600V.

Mat

[Arnoldus]

Hallo Mat,

Ik zal de voorgestelde testen doen, al heb ik zelf al diverse testen gedaan en kon ik geen afwijkingen constateren.
Maar ik ben op dit moment alleen ~7500 Km van huis....

Wordt volgende maand vervolgt,
Groeten,
Arnold

[MatNieuw]

Hi Arnoldus,

for the benefit of others (and especially JYEtech itself) please keep messages in English.
No hurry for testing. If you have problems testing and you live near the center of the Netherlands, I might be able to help.

Mat