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Old 13th April 2013, 06:28 PM   #1761
Salas is offline Salas  Greece
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Quote:
Originally Posted by stajo View Post
I've got this crap to measure HV

And some pix on ripple out. First with noice unfiltered, second with a 10 kHz lowpass filtering
That's an active differential "probe". Its for having CMRR. Doesn't the PicoScope accept a normal single ended coaxial probe also?
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Old 13th April 2013, 06:33 PM   #1762
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How high a voltage AC/DC can a direct Pico input accept safely?
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Old 13th April 2013, 06:40 PM   #1763
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From Pico website:

Our active differential probes let you use a conventional earthed oscilloscope to measure signals that are not referenced to ground, including mains voltages. They can also be used to measure and observe the waveforms of three–phase supplies or the gate and control signals of semiconductor circuits. They are ideal for investigating motor speed controls, uninterruptible power supplies, switch mode power supplies and process controllers.

"not referenced to ground"
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Old 13th April 2013, 06:48 PM   #1764
stajo is offline stajo  Sweden
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Can it read HZ at mV level? Press the frequency button for input and output probing.
Before I contemplate over what you just say I did some DMM measures below.
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Its suspiciously same level for in and out now, it could all be riding on the ground loop. Dress the long output cables in twisted pairs. Force pair, sense pair. Remeasure. Null the sense pair by jumpers at F0,S0 F+,S+. Remeasure.
Left shorted (damn unpealable old Ericsson phone cabling) and twisted, right jumpered.

75 mV left and 76 right with DMM
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Old 13th April 2013, 06:55 PM   #1765
stajo is offline stajo  Sweden
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Quote:
Originally Posted by Salas View Post
That's an active differential "probe". Its for having CMRR. Doesn't the PicoScope accept a normal single ended coaxial probe also?
Quote:
Originally Posted by Salas View Post
How high a voltage AC/DC can a direct Pico input accept safely?
Input ranges ±10 mV, ±20 mV, ±50 mV, ±100 mV, ±200 mV, ±500 mV, ±1 V, ±2 V, ±5 V, ±10 V, ±20 V
DC accuracy (% of full scale) ±0.25% (±0.5% on ±50 mV range , ±1% on ±20 mV range

I have normal probes 1x and 10x, maybe I should get others? The Diff probe makes hell of a noice by itself.
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Old 13th April 2013, 06:56 PM   #1766
stajo is offline stajo  Sweden
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Originally Posted by Salas View Post
From Pico website:

Our active differential probes let you use a conventional earthed oscilloscope to measure signals that are not referenced to ground, including mains voltages. They can also be used to measure and observe the waveforms of three–phase supplies or the gate and control signals of semiconductor circuits. They are ideal for investigating motor speed controls, uninterruptible power supplies, switch mode power supplies and process controllers.

"not referenced to ground"
Im putting a clip to earthground when I use it.
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Old 13th April 2013, 07:03 PM   #1767
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All the weird stuff you see are related to ground is highly possible I am afraid. Both system ground and measurement loop ground. Can you show the full diagram of rectification/filter wiring up to the regs?
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Old 13th April 2013, 07:16 PM   #1768
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Originally Posted by stajo View Post
Input ranges ±10 mV, ±20 mV, ±50 mV, ±100 mV, ±200 mV, ±500 mV, ±1 V, ±2 V, ±5 V, ±10 V, ±20 V
DC accuracy (% of full scale) ±0.25% (±0.5% on ±50 mV range , ±1% on ±20 mV range

I have normal probes 1x and 10x, maybe I should get others? The Diff probe makes hell of a noice by itself.
Beyond the ranges of the Pico you quote there should be some max voltage input spec printed right on the scope box next to its input BNC. That should be respected in all occasions. A x10 or x100 probe cuts the input voltage by its dividing ratio. One danger is you accidentally throw the switch to x1 when on HV and bye bye Pico, another danger not common in what you do is you try measure some high amplitude very high frequency signal that the probe can not stand. Because they lose voltage spec progressively with frequency. They can be 300V up to 30kHZ, 100V by 1MHZ, 40V by 10MHZ and keep on falling for instance. There are fixed ratio probes without switches that are better optimized also. Keep in mind when you use X10 you lose 20dB SNR for measuring noise, 40dB for X100.
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Old 13th April 2013, 07:16 PM   #1769
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The strange thing is that I had almost the same figures yesterday with a completely other PSU. Im beginning to untrust my measures.

Edit. Ehrm, ofc last filtercaps goes to each line.
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Last edited by stajo; 13th April 2013 at 07:27 PM.
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Old 13th April 2013, 07:19 PM   #1770
stajo is offline stajo  Sweden
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Originally Posted by Salas View Post
Beyond the ranges of the Pico you quote there should be some max voltage input spec printed right on the scope box next to its input BNC. That should be respected in all occasions. A x10 or x100 probe cuts the input voltage by its dividing ratio. One danger is you accidentally throw the switch to x1 when on HV and bye bye Pico, another danger not common in what you do is you try measure some high amplitude very high frequency signal that the probe can not stand. Because they lose voltage spec progressively with frequency. They can be 300V up to 30kHZ, 100V by 1MHZ and 40V by 10MHZ and falling for instance. There are fixed ratio probes without switches that are better optimized also. Keep in mind when you use X10 you lose 20dB SNR for measuring, 40dB for X100.
It says max 20 V on the Pico by the BNCs. Should I get some passive high attenuation probes (besides a new scope)
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