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'[EE] 10x Oscilloscope probe 'kit' - or similar'
2010\05\12@204949 by Forrest W Christian

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In my R&D and test environments, I seem to quite often need a 'custom'
scope probe..   For instance - RJ45 'probe' end, 10X.  To date, I
basically sacrifice an inexpensive 10x probe and end up with an ugly and
sometimes not all that mechanically stable (long term) cable with the
scope probe basically being turned into a 'bump' on the cable.   I
really dislike doing this because it just isn't the right way.

I'd love to find a pre-manufactured (or kit) 10x probe circuit board
which basically plugs into the scope and has all the compensation
circuitry, to which I can connect my own cable and/or connector to it.  
Even flying leads would be an improvement mechanical.

I asked a few months back about schematics or similar, and got a couple
of responses, but realize that really what I'm looking for is something
I don't have to mess with designing another circuit.  I'm ok with
soldering one up if I need to, but really want the 'hard work' done for
me...

Is anyone aware of a 10X scope probe which is reasonably inexpensive and
terminates to flying leads, or is provide-your-own-cable instead of the
traditional electronics-in-a-real-probe design?

-forrest

2010\05\13@003140 by Sean Breheny

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Hi Forrest,

I use various attachments which go on the end of a regular 10x probe.
I got mine from:

http://www.probemaster.com/shop/index.php

more specifically:

http://www.probemaster.com/shop/index.php?cPath=2_4

They have a "dual lead adapter" which plugs onto the end of most 10x
probes and provides two short (about 10 cm) leads which terminate in
small socket crimp terminals with shrink wrap insulation.

These two little leads can then be plugged onto various items, such as
their SMD grabbers. They have them in a 10 piece set which is for 0.05
inch and larger pitch, and then they sell pairs of super fine ones,
which will go down to 0.02 inch and perhaps even smaller.

You can also use the larger pitch SMD grabbers to grab wires on the
end of a connector, or you could solder pins onto the connector which
will mate with the socket terminals on the "dual lead adapter"


Sean



On Wed, May 12, 2010 at 8:49 PM, Forrest W Christian <spam_OUTforrestcTakeThisOuTspamimach.com> wrote:
{Quote hidden}

>

2010\05\13@073450 by Olin Lathrop

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Forrest W Christian wrote:
> all the compensation circuitry,

You make it sound so fancy.  It's just two resistors, two caps, and a
trimcap.  Big deal.


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Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2010\05\13@075418 by Russell McMahon

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>> all the compensation circuitry,

> You make it sound so fancy.  It's just two resistors, two caps, and a
> trimcap.

For many values of 'just'.

Some seem to use 'not quite normal' coax cable as part of their
overall signal shaping. ie not lowest loss and maybe even custom loss
characteristics.

Peeking inside some Tektronix probes suggests that may use unusual
values of Just.

Some use active probes, though that's not what was being referred to.

Roll yer own 1 Ghz probe.
Beautiful it's not.
Functional it may be.
Its frequency compensation (step 5) uses an extremely unusual value of Just :-)

     http://www.emcesd.com/1ghzprob.htm

Overview

        http://zone.ni.com/devzone/cda/ph/p/id/17

Informative
Fig 1 covers basic issues.

    http://www.sigcon.com/Pubs/straight/probes.htm

2010\05\13@082304 by Olin Lathrop

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Russell McMahon wrote:
> Roll yer own 1 Ghz probe.
> Beautiful it's not.
> Functional it may be.
> Its frequency compensation (step 5) uses an extremely unusual value
> of Just :-)

I wasn't suggesting this for such high bandwidths.  I was thinking of a 10x
probe for a "normal" scope with 60 or 100 MHz bandwidth.  That can be
(usually is) done with two resistors, two caps, and a trim cap.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2010\05\13@085350 by Alan B Pearce

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> Some seem to use 'not quite normal' coax cable as part of their
> overall signal shaping. ie not lowest loss and maybe even custom loss
> characteristics.

I believe one trick that has been done is to use a resistive centre
conductor, to help reduce reflections in the cable. I have seen scope probe
cables where the inner insulation has an 'oversize' hole, and the centre
conductor appears to be a fine nichrome wire that does a zigzag down the
large hole. The hole would appear to be about 10x the wire diameter.

2010\05\13@113436 by Mark Rages

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On Wed, May 12, 2010 at 7:49 PM, Forrest W Christian <.....forrestcKILLspamspam@spam@imach.com> wrote:
{Quote hidden}

The eevblog had an interesting segment on building a high-voltage
scope probe.  Not exactly what you're asking about, but worth the ten
minutes to watch.

Regards,
Mark
markrages@gmail

--
Mark Rages, Engineer
Midwest Telecine LLC
markragesspamKILLspammidwesttelecine.com

2010\05\13@151811 by Forrest W Christian

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On 5/13/2010 6:23 AM, Olin Lathrop wrote:
> I wasn't suggesting this for such high bandwidths. I was thinking of a
> 10x probe for a "normal" scope with 60 or 100 MHz bandwidth. That can
> be (usually is) done with two resistors, two caps, and a trim cap.
Do you by chance have a pointer to a schematic?  I figured that was all
it was to a probe inside (or something similar), but to date have not
found a single schematic which actually shows how said resistors and
caps might be arranged for a 10x probe..

The articles I've seen are either way overcomplicated (like here's all
the stuff you would ever know to make a perfect probe)... or terse on
details (like you probably provided about as many details as the whole
article contains about the contents).

I'm more than able/willing to put together a small pcb with a
right-angle BNC and the right stuff... but really haven't been able to
figure out the right values and arragement for the resistors/caps

-forrest

2010\05\13@160847 by Mike Hagen
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Your custom wiring is the problem, do the compensation at the
measurement site.
Maybe use 50 ohms scope input, then use coax?  Most of my scopes have a
switch to make them 50 ohms.
The good probe manufactures (spelled Expensive) have had to design their
own cable.

Cheap scope cables, for instance may create noise just by being moved,
like if you were monitoring something vibrating.
A shaker or motor test?  A sort of piezoelectric effect.
Tek warns that in some of there probe brochures.
Search their site for info?

2010 8:34 AM, Mark Rages wrote:
{Quote hidden}

2010\05\13@163426 by Olin Lathrop

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Forrest W Christian wrote:
>> I wasn't suggesting this for such high bandwidths. I was thinking of
>> a 10x probe for a "normal" scope with 60 or 100 MHz bandwidth. That
>> can be (usually is) done with two resistors, two caps, and a trim cap.
> Do you by chance have a pointer to a schematic?  I figured that was
> all it was to a probe inside (or something similar), but to date have
> not found a single schematic which actually shows how said resistors
> and caps might be arranged for a 10x probe..

Please put a blank line between what you are quoting and what you are
replying to.  It makes each easier to see.

As for the circuit, start with a resistor divider.  That's where the two
resistors come from.  Then realize that at high frequencies the divide ratio
is likely not the same due to capacitance.  So you put a capacitor accross
each resistor to make a capacitive divider too.  If the ratio of the
resistor divider and the capacitor divider are the same, then all
frequencies get equally attenuated.  Then realize that capacitors aren't
that accurate, so you put a trim cap in series or parallel with one of the
caps.  This is just big enough to trim the capacitive divider to the same
ratio as the resistive divider given all the slop and stray capacitance.
That trimmer is what the probe compensation screw adjusts.  You diddle it
until the square wave out looks like the square wave in, which is a simple
way to tell visually on the scope whether all frequencies are being
attenuated by the same factor.

If this is a 10x probe for a existing scope with a known input impedence,
then you can use the scope as the bottom half of the divider.  The input
characteristics are usually marked on the scope.  For example the one on my
bench says 1Mohm in parallel with 16pF.  In theory a 10x probe would
threfore be 9Mohm and 1.8pF in parallel, all in series with the scope input.
In practise it'll be rather more finniky than that, with the cable
characteristics also taken into account.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2010\05\13@164040 by Marcel Duchamp

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part 0 44 bytes
his is a multi-part message in MIME format.
part 1 1702 bytes content-type:text/plain; charset=ISO-8859-1; format=flowed (decoded 7bit)

On 5/13/2010 12:18 PM, Forrest W Christian wrote:
> On 5/13/2010 6:23 AM, Olin Lathrop wrote:
>> I wasn't suggesting this for such high bandwidths. I was thinking of a
>> 10x probe for a "normal" scope with 60 or 100 MHz bandwidth. That can
>> be (usually is) done with two resistors, two caps, and a trim cap.
> Do you by chance have a pointer to a schematic?  I figured that was all
> it was to a probe inside (or something similar), but to date have not
> found a single schematic which actually shows how said resistors and
> caps might be arranged for a 10x probe..
>
> The articles I've seen are either way overcomplicated (like here's all
> the stuff you would ever know to make a perfect probe)... or terse on
> details (like you probably provided about as many details as the whole
> article contains about the contents).
>
> I'm more than able/willing to put together a small pcb with a
> right-angle BNC and the right stuff... but really haven't been able to
> figure out the right values and arragement for the resistors/caps
>
> -forrest

google image search: "10x scope probe schematic"

As seen in the attached gif, the "average" 10x scope probe has two
parts: a 9Meg resistor in parallel with a variable capacitor.  That's
all.  If it is a deluxe 1x/10x probe, it will have an SPST switch around
the RC network to switch to 1x.  This implies that it requires your
scope to have a 1Meg input which is usually shunted by 20pF, as shown.
Some probes will use a fixed cap in parallel with a trimmer cap.

Some scopes are different than this, YMMV, etc.


part 2 4052 bytes content-type:image/gif; (decode)


part 3 35 bytes content-type:text/plain; charset="us-ascii"
(decoded 7bit)

2010\05\13@170051 by Michael Watterson

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Mike Hagen wrote:
> Your custom wiring is the problem, do the compensation at the
> measurement site.
> Maybe use 50 ohms scope input, then use coax?  Most of my scopes have a
> switch to make them 50 ohms.
> The good probe manufactures (spelled Expensive) have had to design their
> own cable.
>  
Most scopes are 1M Ohm and a certain capacitance in parallel.

In the unlikely event I need 50 Ohm I use a T  and  50 Ohm terminator.
I've never seen scopes with a 50 ohm switch, what make/model/bandwidth?


Spectrum Analysers usually 50 Ohm (or 75 for TV/Cable/Sat orientated models)


On 10:1 probes. There are two kinds.
1) compensation at plug end, often not switched
2) compensation at probe end. may be switched 1:1 also

Basically uses a 10M Ohm resistor with a parallel capacitor, simplest
probe, that is mid point of 1/10th value of cable capacitance + socket
capacitance and you adjust with a square wave source to have square
wave. Too much capacitance and there is a spike and too little and the
probe 10M in series with input & cable capacitance makes  a low pass
filter and the  square wave is  rounded.

You can simply have a 2:1 probe by  having  the  input  1M Ohm  and  a
capacitor same value as inout as input in parallel with it, and then a
small trimmer cap across that to adjust for cable capacitance etc. That
can be in a small pod two pins of IC socket as input and 0.7m of RG174
coax to a BNC plug at scope. Then another turned pin IC socket can be
plug with short wires and clips, or short wire to RJ45 etc..

Note that because of compensation capacitor, even a 10:1 probe can pull
a crystal oscillator or even kill it. I usually use a series 1M resistor
with no capacitor across it on tip of 10:1 probe. The level is then
inaccurate, but you can see it work.

My counter is only high impedance up to 1MHz, Above that it's 50Ohm. In
either case you can't connect it direct to crystal. Some Scopes have a Y
channel out, and that can drive the counter.



2010\05\13@170504 by Michael Watterson

face picon face
Olin Lathrop wrote:
>
> If this is a 10x probe for a existing scope with a known input impedence,
> then you can use the scope as the bottom half of the divider.  The input
> characteristics are usually marked on the scope.  For example the one on my
> bench says 1Mohm in parallel with 16pF.  In theory a 10x probe would
> threfore be 9Mohm and 1.8pF in parallel, all in series with the scope input.
> In practise it'll be rather more finniky than that, with the cable
> characteristics also taken into account.
>
>
> *

all well explained and arrived just after I clicked send on my post. I  
made mistake. I put 10M, which wrong, that would be 11:1

Anyhow if it suits your needs you can make a 2:1, 5:1 20:1 or 100:1, The
main reason for 10x is that it's easy to move a decimal  point  rather  
than  divide  or multiply by 2

2010\05\13@171157 by Michael Watterson

face picon face
Forrest W Christian wrote:
> On 5/13/2010 6:23 AM, Olin Lathrop wrote:
>  
>> I wasn't suggesting this for such high bandwidths. I was thinking of a
>> 10x probe for a "normal" scope with 60 or 100 MHz bandwidth. That can
>> be (usually is) done with two resistors, two caps, and a trim cap.
>>    
> Do you by chance have a pointer to a schematic?  I figured that was all
> it was to a probe inside (or something similar), but to date have not
> found a single schematic which actually shows how said resistors and
> caps might be arranged for a 10x probe..
I meant to post these

I think olin has clearly answered
here anyway (all same thing)
web.njit.edu/~gilhc/ECE291/ECE291VII.htm
http://www.emcesd.com/1ghzprob.htm

For low impedance circuit via a RJ45 plug the 1X probe might do
http://www.cromwell-intl.com/radio/probes.html

2010\05\13@183352 by Adam Field

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> In the unlikely event I need 50 Ohm I use a T  and  50 Ohm terminator.
> I've never seen scopes with a 50 ohm switch, what make/model/bandwidth?

My LeCroy 9354CTM does. It's a four channel 500MHz. The impedance is
selectable between 1M and 50 ohms. I can also select the probe
attenuation between 1 and 10k with about 10 steps in between
(2,5,10,etc).

2010\05\14@002142 by Sean Breheny

face picon face
There are quite a few that have this feature. The Tek TDS3000 series
have a menu option, even for the 100MHz variants (i.e., not a physical
switch, although I think you can hear a relay click inside when you
change the option). I have a Tek 2465 DMS, which is a late 1980s
analog scope, 300MHz, and it has a selector switch for AC,DC,GND, or
50 Ohm DC coupled for two of its four channels.

Of course, the problem with using the 50 ohm input for most things is
that it would load down the circuit greatly. This mode is mainly meant
for attaching active probes which buffer the signal at the probe tip
OR for viewing the output of a 50 ohm RF system (at low power).

Sean


On Thu, May 13, 2010 at 6:33 PM, Adam Field <EraseMEadamspam_OUTspamTakeThisOuTbadtech.org> wrote:
>> In the unlikely event I need 50 Ohm I use a T  and  50 Ohm terminator.
>> I've never seen scopes with a 50 ohm switch, what make/model/bandwidth?
>
> My LeCroy 9354CTM does. It's a four channel 500MHz. The impedance is
> selectable between 1M and 50 ohms. I can also select the probe
> attenuation between 1 and 10k with about 10 steps in between
> (2,5,10,etc).
>
>

2010\05\14@005724 by Forrest W Christian

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face
Thanks everyone ... exactly what I needed.    Probably will end up
making a small PCB with the divider, right angle bnc, and trimcap on
it... but now I understand what is going on.

Special thinaks to Olin, Marcel, and Michael Watterson.

And p.s. to Olin:  I wish Thunderbird would leave my formatting alone
when it sends it.  Or more accurately, I miss fixed-width, 80 character
line emails when quoting email.   I am never quite sure what thunderbird
is doing with my email when I hit send...

-forrest

2010\05\14@044559 by Alan B Pearce

face picon face
> In the unlikely event I need 50 Ohm I use a T  and  50 Ohm terminator.
> I've never seen scopes with a 50 ohm switch, what make/model/bandwidth?

Tektronix and Agilent (HP) have such switches on most of their scopes.
Normally part of the AC/DC switch, which may have a 3rd or 4th position
which tends to be GND and 50 ohm termination. I cannot remember if the Tek
7700 series plugins that I had access to had it, but the HP 1740 certainly
did, and that is going back over 30 years.

The Tek TDS2000 series and TDS3000 series scopes I currently use have these
selections as well.

Every 'decent' scope I have come across since then has had all 4 selections
available as I recall.

2010\05\14@050144 by Michael Watterson

face picon face
Alan B Pearce wrote:
> Tektronix and Agilent (HP) have such switches on most of their scopes.
> Normally part of the AC/DC switch, which may have a 3rd or 4th position
> which tends to be GND and 50 ohm termination. I cannot remember if the Tek
> 7700 series plugins that I had access to had it, but the HP 1740 certainly
> did, and that is going back over 30 years.
>
> The Tek TDS2000 series and TDS3000 series scopes I currently use have these
> selections as well.
>
> Every 'decent' scope I have come across since then has had all 4 selections
> available as I recall.
>
>  
These must be scopes made after 1980s :-)  ?

My Spectrum Analyser is an HP141T. My Tektronix and Hameg are similar
vintage.

2010\05\14@054608 by Electron

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At 10.46 2010.05.14, you wrote:
>> In the unlikely event I need 50 Ohm I use a T  and  50 Ohm terminator.
>> I've never seen scopes with a 50 ohm switch, what make/model/bandwidth?
>
>Tektronix and Agilent (HP) have such switches on most of their scopes.
>Normally part of the AC/DC switch, which may have a 3rd or 4th position
>which tends to be GND and 50 ohm termination. I cannot remember if the Tek
>7700 series plugins that I had access to had it, but the HP 1740 certainly
>did, and that is going back over 30 years.
>
>The Tek TDS2000 series and TDS3000 series scopes I currently use have these
>selections as well.

I have a TDS2024 and I see no such 50ohm switch.


>
>Every 'decent' scope I have come across since then has had all 4 selections
>available as I recall.
>
>-

2010\05\14@091503 by Sean Breheny

face picon face
I'm not sure about your particular model, but have a look under the
vertical menu. In other words, select a channel and press the MENU
button under the vertical section. Somewhere in the vertical menu
structure should be a 50 ohm termination option.

Sean


On Fri, May 14, 2010 at 5:45 AM, Electron <electron2k4spamspam_OUTinfinito.it> wrote:
{Quote hidden}

>>

2010\05\14@134227 by Mike Hagen

picon face
 On 5/13/2010 2:00 PM, Michael Watterson wrote:

"Most scopes are 1M Ohm and a certain capacitance in parallel.

In the unlikely event I need 50 Ohm I use a T  and  50 Ohm terminator.
I've never seen scopes with a 50 ohm switch, what make/model/bandwidth?"





I have probable 10 scopes and 20 or more plugins for TEK 7904A
These are at my other residence.

A lot of those have 50 or 75 ohm inputs.
It is sad, my favoite scope, the 7904A, they die sitting from age.
I only have one of 3 working.  They get HV problems sitting at my house
down the hill.
It is a few miles from the beach, the humidity is higher there.
Really hard to fix and find parts for them.

I checked up here in the mountains where I also have a few.
My old HP1704A (100MHz) has 75 ohm option switch on channel A

The HP 54615B (500MHz) has 50 ohm option on menu both channels.

My old Fluke 97 may have it too, but batteries are always dead so I
could not verify that.

I have a 4 channel HP that runs windows inside, I bought on eBay.  It is
at my other house.
It is 2 GHZ.  New about $30K?, I paid $3600 for it.  My BABY!
Can't ever remember the model.  It has 50 Ohm options on all channels too.

So I guess most of MINE do?


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