Author Topic: Why are scope probes so damn big?  (Read 6593 times)

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Offline tggzzz

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Re: Why are scope probes so damn big?
« Reply #25 on: November 09, 2018, 04:26:40 pm »
It's also the fact that most circuits now are digital and have self test makes probing and scopes in general much less useful than they used to be.

Unless you are working in the femtoamp domain or with avalanche photo diodes, your circuit is almost certainly analogue. The voltages (or currents, as appopriate) are then interpreted to be a digital signal. "Signal integrity" is the name given to the engineering necessary to ensure and verify that the voltage/current is correctly interpreted as a digital signal. Verifying signal integrity is usually done with analogue instruments, e.g. scopes. (In some cases it is done indirectly by measuring BER and similar.)

Once signal integrity is verified, it is best to flip to the digital domain, e.g. logic analysers or printf statements.

Hence there is still a need for analogue probing, but doing this is far more difficult (and expensive) that it used to be. Tektronix recently introduced a probe tip that, IIRC, cost $10 every time it touched a circuit!
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Offline ConKbot

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Re: Why are scope probes so damn big?
« Reply #26 on: November 09, 2018, 04:37:37 pm »
They make small probes too, like this for example:
https://www.keysight.com/en/pd-1661742-pn-N2874A/passive-probe-101-15-ghz-13-m?cc=US&lc=eng

I have a similar set of probes from Agilent and they are indeed very nice probes.

It doesn't make sense making them smaller than this because then they can no longer be held like a pen, and you don't really gain much from going smaller. If you need a tiny probe to solder in then just cut the end off a BNC cable.

Yep, I had a work scope that came with the N2872A probes, or maybe even an earlier version. The cable on the N2872A looks a bit heavier then the cable on the ones on the scope. Nice fine point, tip is tiny without the grabber attached and still pretty small with the grabber.

 

Offline rsjsouza

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Re: Why are scope probes so damn big?
« Reply #27 on: November 09, 2018, 05:08:43 pm »
Pomona seems to have a very thin probe. It is not cheap, though:
https://www.all-spec.com/Manufacturers/Pomona/Test-Measurement/Oscilloscopes-Accessories/Oscilloscope-Probes/6551-19816

Or you can have as many types of BNC breakouts as you want:
https://www.pomonaelectronics.com/products/cables/bnc-breakouts

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Offline mikeselectricstuff

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Re: Why are scope probes so damn big?
« Reply #28 on: November 09, 2018, 06:15:36 pm »
The issue is often as much the stiffness of the cable as the size of the probe - light silicone cables would be a lot nicer.

Attatched pic is how I very often use the light Tek probes
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Offline Mechatrommer

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Re: Why are scope probes so damn big?
« Reply #29 on: November 10, 2018, 05:26:29 am »
i dont have proper panavise, heavy articulated arm or such and my bench is really small, so i need to improvise with 3d printed part, printed a few such as the green one at the front, and yellow at the back (broken i guess due to lee crap PLA material), currently probes are held by transparent parts. circuit to probes using lee crap china micro grabber that i have to re-bend the tip to original shape very so often... fwiw...
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Offline Mechatrommer

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Offline David Hess

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Re: Why are scope probes so damn big?
« Reply #31 on: November 11, 2018, 11:06:57 pm »
There is a very specific and stupid reason for this.

A couple decades ago, UL and the other regulatory agencies got involved and forced the creepage and clearance rules to be applied to test instrument probes and connectors.  The result was all of the standard subminiature 400 volt oscilloscope probes being removed from the market and multimeters and other test instruments losing their more convenient binding posts for guarded connectors.

The exact date can be tracked down by looking through the old Tektronix catalogs to find exactly when the standard subminiature probes were removed.
 

Online KE5FX

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Re: Why are scope probes so damn big?
« Reply #32 on: November 11, 2018, 11:29:55 pm »
There is a very specific and stupid reason for this.

A couple decades ago, UL and the other regulatory agencies got involved and forced the creepage and clearance rules to be applied to test instrument probes and connectors.  The result was all of the standard subminiature 400 volt oscilloscope probes being removed from the market and multimeters and other test instruments losing their more convenient binding posts for guarded connectors.

The exact date can be tracked down by looking through the old Tektronix catalogs to find exactly when the standard subminiature probes were removed.

Eh, I don't know if I buy that.  Why not just keep selling the same probes, but re-rate them for 48V max?
 

Offline Wolfgang

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Re: Why are scope probes so damn big?
« Reply #33 on: November 11, 2018, 11:34:44 pm »
First, "normal" probes are made to be held by human hands and this means that they have a size where is is easy.

If you need it very small probes making reliable contacts with alligator clips and tips comes to a limit when you think of 0.2mm spaced FPGA pins or the like.

Keysight and others have made very small probes that can be soldered into a circuit to keep stray capacitances and lead inductance to a minimum  for hight frequency measurements. They cost a fortune, however, and  the soldering part needs a microscope.

What you can do is homebrew a small FET probe that can be soldered into a circuit, like here:

https://electronicprojectsforfun.wordpress.com/rf-measurement-techniques/high-frequency-probes/

 

Offline David Hess

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Re: Why are scope probes so damn big?
« Reply #34 on: November 13, 2018, 01:31:48 am »
There is a very specific and stupid reason for this.

A couple decades ago, UL and the other regulatory agencies got involved and forced the creepage and clearance rules to be applied to test instrument probes and connectors.  The result was all of the standard subminiature 400 volt oscilloscope probes being removed from the market and multimeters and other test instruments losing their more convenient binding posts for guarded connectors.

The exact date can be tracked down by looking through the old Tektronix catalogs to find exactly when the standard subminiature probes were removed.

Eh, I don't know if I buy that.  Why not just keep selling the same probes, but re-rate them for 48V max?

The story came from a guy who worked at Tektronix when the new rules came down and they had to sacrifice their existing subminiature probe lines.  I confirmed it later by finding the change in their catalogs and like I said, multimeters were also affected, no more binding posts.
« Last Edit: November 21, 2018, 06:49:48 pm by David Hess »
 

Offline Berni

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Re: Why are scope probes so damn big?
« Reply #35 on: November 13, 2018, 06:39:47 am »
First, "normal" probes are made to be held by human hands and this means that they have a size where is is easy.

If you need it very small probes making reliable contacts with alligator clips and tips comes to a limit when you think of 0.2mm spaced FPGA pins or the like.

Keysight and others have made very small probes that can be soldered into a circuit to keep stray capacitances and lead inductance to a minimum  for hight frequency measurements. They cost a fortune, however, and  the soldering part needs a microscope.

What you can do is homebrew a small FET probe that can be soldered into a circuit, like here:

https://electronicprojectsforfun.wordpress.com/rf-measurement-techniques/high-frequency-probes/

That is a pretty sweet looking active probe. I do already have some Agilent 1152A probes for when i want a active one. But boy are those probes the opposite direction of this thread topic. The probes are huge and heavy with a thick stiff cable, the new ones are better in that regard.
 

Offline Mechatrommer

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Re: Why are scope probes so damn big?
« Reply #36 on: November 13, 2018, 07:45:28 am »
But boy are those probes the opposite direction of this thread topic. The probes are huge and heavy with a thick stiff cable, the new ones are better in that regard.
look further down, i guess he's talking about the diy/specialized fet circuit that is soldered directly onto the pcb, i guess we should do the same once we passed certain threshold. there is no probe that is good for everything. and that bulky keysight probe is not meant to sit directly on the pcb, it has veriety of small tips suited for certain pcb circuit.
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