I’ve a PCSU1000 for many monthes mow, and I’m quite happy, but I’ve seen a strange thing.
what ever the PC I use.
what ever the probe I use (shunted obviously)
even if I put the PCSU in a faraday cage I still see the artifact in the FFT.
here is the artifact (probe set with x1) (scale = log x1) (average function)
my question is :
is this normal ?
(the major problem is that this 70Khz artifact can also be seen on other scales (probe x10 / scale 20V -> artifact at -12.7dBV)
If no … where does that come ?
any idea ?
Thank you for the notification report.
Indeed, there seems to be an internal spurious signal at about 77kHz.
This signal is not coming from the oscilloscope probe.
You can check this by selecting the GND connection. The signal you see in this case is not a “real” input signal and can be omitted.
I’ve a look to the sch file of the PCSU1000 and this capacitor is used for the decoupling of a 3.3V Regulator.
I have in stock tantalium capacitors (1-10µF) as well as MKT/MKP of various values… SO if you estimate that something else that an std electrolytic capacitor will be best suited, please let me know.
it seems that the regulator does not like too low ESR, but I prefer to ask you to confirm.
[quote]it seems that the regulator does not like too low ESR, but I prefer to ask you to confirm.[/quote] You are right. Better to use a standard electrolytic capacitor. It has high enough ESR.
[quote]is there any other Harware upgrade that could improve the PCSU1000?[/quote]This is the only upgrade at the moment. This upgrade is based on your notification.
[quote]Thanks… Will keep you informed of the result
[/quote]I hope it helps…
If you have a look in detail, you will see that the level of noise has been rejected of at least 6dB (Globally)
I still have sharp peaks, but I suspect the power supply of my computer there.
I’ve checked few additional thing and this really improve the noise rejection
I don’t know if the PCSU is still produced, but if it is the case, you should ask a small change …
did you try to see what’s going on if we use a nice regulated Power supply instead of the USB 5V?
I’ve In my stock few regulated Power supply that could fit, BUT To do so I need to CUT on the PCB, and I do not want that !
Maybe in few monthes … who knows.
[quote]I don’t know if the PCSU is still produced, but if it is the case, you should ask a small change …
did you try to see what’s going on if we use a nice regulated Power supply instead of the USB 5V?[/quote] This is good idea for the future products.
Yesterday I made a mistake… (not 100% sure … but)
Following the previous impressive change on the PCSU1000, I’ve decided to add A certain number of additional 100µF electrolytic caps in parallel of a certain 10µF Caps, and a 2200µF in parallèle of a CAP just near the 5V USB Input.
the objective was to have the best noise reduction possible.
(I’ve put 100µF in parallel with C68, C85, C42, C18, C78, C73, C71 - and 2200µF in parallel with C70.)
When I start up the PCSU everything was fine… then after few minutes the 2nd Channel began to evolve.
I try a calibration, and the PCSU was not able to re calibrate.
Then i decided to remove all the CAps I’ve put additionnaly …
But I still Had the problem with the second channel.
This morning it was still the same, but i’ve let the PCSU connected to my computer with the software running.
After 30 minutes or SO, without any reason, the PCSU was able to recalibrate.
ANy idea on the phenomena ?
Is the issue linked to my (caps additions) ?
for information, in the las past few months I’ve few problems with the calibration when startin the PCSU.
Thanks in advance for your suport.
EDIT : extract of the calibration LOG
CH1 offset at 2V/div : 122 OK
CH2 offset at 2V/div : 174 FAIL
CH1 offset at 1V/div : 1 OK
CH2 offset at 1V/div : 37 OK
CH1 offset at 0.5V/div : 3 OK
CH2 offset at 0.5V/div : 38 OK
CH1 offset at 5us/div : 2 OK
CH2 offset at 5us/div : 38 OK
CH1 Y-position low 32
CH1 Trigger : 53
CH1 Trigger : 45
CH1 Trigger low : 49 OK
CH1 Y-position mid 128
CH1 Trigger : 94
CH1 Trigger : 90
CH1 Trigger middle : 92 OK
CH1 Y-position high 223
CH1 Trigger : 138
CH1 Trigger : 132
CH1 Trigger high : 135 OK
CH2 Y-position low 32
CH2 Trigger : 76
CH2 Trigger : 67
CH2 Trigger low : 72 OK
CH2 Y-position mid 128
CH2 Trigger : 187
CH2 Trigger : 179
CH2 Trigger middle : 183 OK
CH2 Y-position high 150
CH2 Trigger : 214
CH2 Trigger : 205
CH2 Trigger high : 210 FAIL
EXT Trigger middle : 40 OK
I’ve worked on my pcsu1000.
finally I’ve added a 2200µF cap in parallel with the C70, and a 100µF in parallel with C12.
The caps i try to put in parallel with C71 C78 and C68 or C73 and C85 pose a problem with the regulators that are very close.
The impedance seen by the regulator pose probelm, and the PSCU does no want to start at all.
here is the result now. It is still not 100% clean but this is better than before, and much better than originally.
Thank you for doing these tests.
I’m sorry for the problems you encountered.
The CH2 problem may or may not be related to the additional capacitors.
[quote]finally I’ve added a 2200µF cap in parallel with the C70, and a 100µF in parallel with C12.[/quote]The C70 is directly connected to the USB +5V supply. The capacitor value is rather high.
The problem is that the USB output may detect too high charge current and disconnect the +5V supply.
I apologize for jumping in.
I was wondering have you tried this on a different system?
My thought is maybe your power supply (+5V) in you system might be having an issue.
I’ve at home 3 laptop and a desktop, and the result (original issue) is the same on all computers.
i did not try to compare since I’ve done the change … maybe there are differences between computers.
Well noted (regarding the in rush current). For the moment everything is working fine now, but this may be dangerous for the computer (long term).
[quote]I’m thinking about using a regulated PSU.[/quote]One alternative may be to use a self powered USB HUB. You may replace the +5V power adaptor of the HUB (if not good enough) with a regulated PSU.
FWIW I had a bit of time today and found the following using my unmodified PCSU1000 and what I believe is the same setup/configuration as used by the original poster:
CH1 (1 ms/div, coupling Gnd, 125 kS/s):
CH2 (1 ms/div, coupling Gnd, 125 kS/s:
CH1 (0.1 us/div, coupling Gnd, 50 MS/s):
CH2 (0.1 us/div, coupling Gnd, 50 MS/s:
There is that odd plateau around 10 kHz, and a slight bump at 500 kHz or so but that’s about it.
Hi, I just saw this thread, and was wondering if the spike around 10 KHz is related to the 6 KHz voltage pump used to generate the -2.5v reference. The only ripple filter used is the L-C combination C127, L2 after the full-wave rectifier.
Perhaps you’re getting a 2nd harmonic of the 6KHz from F_PUMP?
