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Clarification about floating measurement with an insulated oscilloscope

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lor3n7o:
Taking for sure the following parameters retrieved from the probe and oscilloscope datasheet.
- Oscilloscope input resistance: 1M
- Oscilloscope input capacity: 25pF
-Resistance of the probe when connected to the oscilloscope 5M.
-Capacity of the probe when connected to the oscilloscope 11.2pF.
- 10x probe factor.
I thought of two potential configurations that could be inside the probe if it had components on the reference lead.
I am attaching the datasheet of the probe and a photo of the two configurations that could be in the P5102 probe.
Both are based on the principle of separating the reference lead from the oscilloscope's BNC.
What do you think?

David Hess:
The probe is simpler than that and does not have a balanced input.  Ground goes through without any series resistance.

The P6055 is an example of a x10 probe with 1 megohm input resistance with the same configuration.  The P6009 is an example of a x100 probe with 10 megohm input resistance with the same configuration.

lor3n7o:

--- Quote from: David Hess on March 27, 2021, 02:28:09 am ---The probe is simpler than that and does not have a balanced input.  Ground goes through without any series resistance.

The P6055 is an example of a x10 probe with 1 megohm input resistance with the same configuration.  The P6009 is an example of a x100 probe with 10 megohm input resistance with the same configuration.

--- End quote ---

the p5102 is 10x and 5Mohm. So do you think it would have 9Mohm series resistor to make the 10x partition and in addition an additional 10Mohm resistor at the input to lower the total input resistance to 5Mohm ??
thanks for the replies.

jonpaul:
Bonjour a tous: It seems a lot of related topics in this thread:

Probe use in differential and single ended
Safety ratings
Probe design
Floating portable scopes

It is wise to do a bit of research in this area:

Probes: Tektronix Circuit Concepts Oscilloscope Probe Circuits
https://w140.com/tekwiki/images/6/62/062-1146-00.pdf

Specific models: https://w140.com/tekwiki/wiki/
eg https://w140.com/tekwiki/wiki/P5102

The 30 VAC or 42.2 VDC rating of a scope or probe  is a UL class of SELV = Safety Extra Low Voltage, in theory the max V for touching safety.
P5102 etc are designed to prevent contact and used in dangerous power applications.
The rating in the spec of 30V reflects the UL ratings and protects again liability in case of lawsuit.

I have used scopes and probes since 1960s including on high power and high voltage devices , to 55 kV.

I have seen scopes floated to 20 kV with appropriate precautions (LLNL)

Most TEK 10X probes have a 300-400 V peak rating.

 HV probes P6013, P6015, P6015A have x100, X1000 and ratings to 20 kV, 40 kV peak.

I have never need a differential HV measurement, but used some diff active  HV probes, such as Yokogawa 701921, 700V

Finally ALL of these "safety" probes have so much bulk, insulation and complication that usefulness is low.

Depending on your expérience and the danger of the devices being probed, you must judge if the risk is worth the benefit. Amateur Radio, Broadcast and power engineers know how to work and measure safely. Novices may not.

Kind Regards,

Jon

PS: LEGAL NOTICE  I AM NOT GIVING ANY ADVISE, I HAVE NO LIBAIBLITY IF YOU ARE INJURED OR WORSE!


David Hess:

--- Quote from: lor3n7o on March 31, 2021, 07:09:37 am ---
--- Quote from: David Hess on March 27, 2021, 02:28:09 am ---The probe is simpler than that and does not have a balanced input.  Ground goes through without any series resistance.

The P6055 is an example of a x10 probe with 1 megohm input resistance with the same configuration.  The P6009 is an example of a x100 probe with 10 megohm input resistance with the same configuration.
--- End quote ---

the p5102 is 10x and 5Mohm. So do you think it would have 9Mohm series resistor to make the 10x partition and in addition an additional 10Mohm resistor at the input to lower the total input resistance to 5Mohm ??
--- End quote ---

No, like the examples I give, it has a much lower series resistor of about 4.5 megohms.

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