[ASK] Old Tektronix A6902 vs new high voltage differential probe ?

[BravoV]

Please be gentle as I'm just starting to absorb & learn here about this high voltage probes.

As Tek A6902 is quite old and its called an "isolator" vs current new high voltage differential probe, such as the Sapphire/Pintek/Pintech etc made or the upcoming Dave rebranded HVP70.

I'm aware like HVP70 is capable of 70 Mhz while the Tek A6902 is only at 20 Mhz, but leave the bandwidth out of the equation for a moment, I just want to hear from your thought about these two different HV probes from other aspects.

TIA

[David Hess]

The Tektronix A6902 does not provide a differential input (unless two channels are combined) but has complete galvanic isolation; it effectively has one high impedance connection and one low impedance "ground" for each channel.  There are some specialty DSOs like the Tektronix TPS2000 which provide the same thing on each of their inputs; they are convenient for safely making primary side off-line and power line measurements.

A high voltage differential probe has a differential input with two high impedance connections but does not provide galvanic isolation; it still relies on a third common "ground" connection somewhere.  If you used a differential probe on an isolated input, then it can fail do to the lack of a ground connection which allows the common mode voltage to drift out of range.

[BravoV]

The Tektronix A6902 does not provide a differential input (unless two channels are combined) but has complete galvanic isolation; it effectively has one high impedance connection and one low impedance "ground" for each channel.  There are some specialty DSOs like the Tektronix TPS2000 which provide the same thing on each of their inputs; they are convenient for safely making primary side off-line and power line measurements.

So what are you saying is, basically A6902 turns an ordinary 2 ch scope into this ?

Illustration from Tek's handheld scope manual.


That TPS2000 is interesting, just knew it, quite an unique scope. 

A high voltage differential probe has a differential input with two high impedance connections but does not provide galvanic isolation; it still relies on a third common "ground" connection somewhere. 

Yeah, this is my confusion as well, as I own a low voltage differential probe Tek P6046 that needs its common ground to be connected DUT, while these typical HV differential probe doesn't have any. 

Like below photo on the HV diff. probe, only two differential points needed, why it doesn't need the common ground ?

If you used a differential probe on an isolated input, then it can fail do to the lack of a ground connection which allows the common mode voltage to drift out of range.

What kind of situation or better an example case for this ?

David, thanks a lot for the explanation. 

[David Hess]

So what are you saying is, basically A6902 turns an ordinary 2 ch scope into this ?

Exactly.

That TPS2000 is interesting, just knew it, quite an unique scope. 

Tektronix had much earlier oscilloscopes with the same kind of built in isolation for each channel and other manufacturers have them also.  The TPS2000 was just the first one that came to mind.

If there is an external trigger input, then it will likely also be isolated.

A high voltage differential probe has a differential input with two high impedance connections but does not provide galvanic isolation; it still relies on a third common "ground" connection somewhere.

Yeah, this is my confusion as well, as I own a low voltage differential probe Tek P6046 that needs its common ground to be connected DUT, while these typical HV differential probe doesn't have any. 

Like below photo on the HV diff. probe, only two differential points needed, why it doesn't need the common ground ?

A high voltage differential probe has the same ground requirements as the P6046 and they both have a third connection which is the common or ground whether they provide a separate lead for it or not.

The P6046 is much higher performance than any high voltage differential probe (except maybe for a 7A13 with calibrated probes in some cases) and it has a much lower common mode input voltage range so it provides ground connections at the probe tips.  Usually you do not have to use its ground connections.

A modern high voltage differential probe assumes that the ground connection will be provided through its power supply or the oscilloscope which is the same as the ground for the device under test.  If it is connected to an isolated input like on a TPS2000, then this ground is free to float anywhere which could result in the common mode voltage range of the differential probe being exceeded or even the maximum isolation voltage of the isolated input being exceeded.  This also creates a safety hazard to the user.

If you used a differential probe on an isolated input, then it can fail do to the lack of a ground connection which allows the common mode voltage to drift out of range.

What kind of situation or better an example case for this ?

David, thanks a lot for the explanation. 

This would happen if you used a differential probe with an oscilloscope which has galvanically isolated inputs like the Tektronix TPS2000 and Tektronix has a warning about doing this:

Warning: For safe operation, do not use the P5200A High-voltage Differential Probe with oscilloscopes that have floating inputs (isolated inputs), such as the Tektronix TPS2000 and THS3000 Series oscilloscopes. The P5200A High-voltage Differential Probe requires an oscilloscope or other measurement instrument with grounded inputs.

[BravoV]

David, thank you, all cleared now. 

[Electro Detective]

David, thank you, all cleared now. 

Second that   

Isolation probes, iso transformers and differential measurements can get very merry go round if one has an uncertain grasp,
especially where HV and earth/ground are related.. or non related. 

 

[BravoV]

Blame it on David, I ended this on my desk ... 

Yeah, its huuugeee , the scope's size is nothing compared to it's probe. 

[Electro Detective]

...and ANOTHER relaxing weekend nuked     imprisoned in the lab with another new gadget   

 

[BravoV]

...and ANOTHER relaxing weekend nuked     imprisoned in the lab with another new gadget   

 

Another blame for David, as its performed as expected, and yay .. free from worry at probing any points with mains voltage circuits  , ... but ... sigh ... another relaxing imprisoned life .... 

BUSTED on DEEP, EMI, TEST ... guilty on all counts 

Life is not complete and meaningless without the 2nd B version ... 

BUSTED - Bought Unnecessary Shitload of Test Equipment Devices
DEEP - Duplicated Electronics Equipment Possession
EMI - Equipment Matching Impulse
TEST - Test Equipment Symmetry Transfixation

[EEVblog]

As Tek A6902 is quite old and its called an "isolator" vs current new high voltage differential probe, such as the Sapphire/Pintek/Pintech etc made or the upcoming Dave rebranded HVP70.

It's not upcoming, it's on sale now. Many people on here already have one.
It's on my shop, Amazon US, and very shortly Amazon UK.

[BravoV]

As Tek A6902 is quite old and its called an "isolator" vs current new high voltage differential probe, such as the Sapphire/Pintek/Pintech etc made or the upcoming Dave rebranded HVP70.

It's not upcoming, it's on sale now. Many people on here already have one.
It's on my shop, Amazon US, and very shortly Amazon UK.

Yes, I'm aware of that.

Also the date I posted this thread was at March, at that time your probe was not for sale yet.
If I'm not mistaken the HVP70 was available publicly for sale at your shop about mid of April.

Anyway, I'm content and happy with this A6902s as they're cheap, and performs good enough for hobbyist like me, and also I only probe mains connected circuit on the bench table.