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G8MNY > TECH 29.03.26 17:16l 343 Lines 16011 Bytes #10 (0) @ WW
BID : 55739_GB7CIP
Subj: Scope Probes
Path: JH4XSY<JE7YGF<LU4ECL<LU9DCE<GB7YEW<W9GM<WA2UET<K5DAT<GB7CIP
Sent: 260329/0804Z @:GB7CIP.#32.GBR.EURO #:55739 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Update Jul 20)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
They come in a few standard forms..
1:1 COAX
A terminated teed coax is the only way get the highest bandwidth into your
scope. Simple nothing to adjust!
BNC T SCOPE INPUT LOAD
Input o)==============================ﾂﾄo)ﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾂﾄﾄﾄScope
75/50ohm >ﾙ 75/50ohm coax 75/50R ｳ �25pF=== 1M Attenuators
Termﾀﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾁﾄﾄﾄ& Amp
The scope input capacitance has the minimum effect on the signal.
Only usable on DC-RF 75/50ohm circuits, e.g. DC-200MHz.
Voltage limited to scope input/termination load rating.
Able to see low signal levels, no added calibration errors.
1:1 TEST LEAD
These are straight screened wires like a coax, with just test clips on the ends
and BNC at the scope end. Simple nothing to adjust!
SCOPE INPUT LOAD
Input >ﾄ)================================o)ﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾂﾄﾄﾄScope
1M >ﾄﾙ 200pF of lead Capacitance ｳ �25pF=== 1M Attenuators
225pF e.g. 75ohm coax ﾀﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾁﾄﾄﾄ& Amp
Coax capacitance per foot is about 20/30pF for 75/50ohm.
The capacitance depends on coax impedance & lead length. Only usable on DC AF
and low Z circuits where the loading is not important e.g. DC-3MHz (just about
OK on terminated 75ohm video!)
Voltage limited to scope input.
Able to see low signal levels.
1:1 PROBE
These have one of the 2 sizes of standard probe systems. The spring hook can
changed to a long probe, just the tip or tip covers for small point or IC leg
work, or be adapted to a BNC plug.
Simple nothing to adjust!
PROBE PARTS
Spring Hook ﾞ Tip Probe Coax ___
_________/~~~~~~ﾞ _ﾚﾄﾄﾄﾄﾄﾄﾄ||~~~~~~ｳﾄ- ｳ~'ﾄ-ｿ___\\ ___ﾚ-ﾄ'~ｳ -ﾄｳ ﾃ'~~ｳｳ
c_\________| ﾞ ﾄｴ_ｳ || ｳｳｳ ｳ ｳ ｳ ｳ ｳｳｳ ｳｳ ｳｳ
\______ﾞ ﾀﾄﾄﾄﾄﾄﾄﾄ||______ｳ-ﾄ ｳ_.-ﾄﾙ~~~~ \\~~ﾀﾄ-._ｳ ﾄ-ｳ___ﾃ.__ｳｳ
ﾞ .ﾄ.__ Screw or Screw or
ﾚﾄﾄﾄﾄﾄｿ ｳ ｳ _ｳ Crimp Crimp BNC
Long Probe ﾞ ﾃﾄBNC_ｳ ｳ ｳ ｳ
_________/~~~~~~ﾞ ﾀﾄﾄﾄﾄﾄﾙ ｳ_ｳﾄﾄﾙ
ﾜﾜ\________| ﾞ _ ﾝ Earth
\______ﾞ /~ ｳTip ﾞ Clip
ﾞ \_ ｳShroud ﾝ
~ ﾞ
Input Probe parts SCOPE INPUT LOAD
Load --ﾂﾄLﾂLﾄ)============================ﾄ33Rﾄo)ﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾂﾄﾄﾄScope
1M+ ﾀｴﾃﾙ ｳ 70pF Low capacity 3m leadﾀﾄﾄﾄﾄﾄﾄｳ �25pF=== 1M Attenuators
100pF >ﾄﾄﾄﾄﾄﾄﾄﾙ 300R DC, Z = 150R, (7pF/Ft) ﾀﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾁﾄﾄﾄ& Amp
The load capacitance depends on lead length (1.2, 1.5, 2, or 3m) and the coax
type which here is a very fine single strand core polly foam insulated high
impedance type. There is often a tweak on the probe (tuned circuit + L shown
and a series scope R) to improve HF and pulse performance.
Only usable on DC AF and low Z circuits where the loading is not important.
e.g. DC up to 6-10MHz on 75ohm terminated systems.
Voltage limited by probe & scope. Able to see low signal levels.
10:1 TRIMMED PROBE
These are the most common probe, with in built attenuator reducing input load.
Must be calibrated before use on that scope's input!
Not able to see very low signal levels.
PROBE PARTS
Spring Hook ﾞ Tip Probe Coax ___
_________/~~~~~~ﾞ _ﾚﾄﾄﾄﾄﾄﾄﾄ||~~~~~~~ｳﾄ- ｳ~'ﾄ-ｿ___\\ ___ﾚ-ﾄ'~ｳ -ﾄｳ ﾃ'~~ｳｳ
c_\________| ﾞ ﾄｴ_ｳ || 0 Adjｳｳｳ ｳ ｳ ｳ ｳ ｳｳｳ ｳｳ ｳｳ
\______ﾞ ﾀﾄﾄﾄﾄﾄﾄﾄ||_______ｳ-ﾄ ｳ_.-ﾄﾙ~~~~ \\~~ﾀﾄ-._ｳ ﾄ-ｳ___ﾃ.__ｳｳ
ﾞ
Input Probe parts
Load ﾚｴﾃｿC Adj * SCOPE INPUT LOAD
10M�+ ﾄ47RﾄLﾁ9Mﾁ)============================o)ﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾂﾄﾄﾄScope
15pF >ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ 70pF Low capacity 3m lead ｳ �25pF=== 1M Attenuators
Z = 150R ﾀﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾁﾄﾄﾄ& Amp
The accurate series 9M gives the 10:1 DC calibration with the scope input R.
The trimmer C in the probe has to be exactly 1/9 of the total capacitance of
the scope & lead, then the probe's frequency and phase (pulse) response will be
flat. So the probe is designed for a particular lead! Note the more complex
tiny probe components are to improve bandwidth & pulse responce.
Usable DC-60MHz (3.5nS rise time). Voltage limited by probe design/10x scope
input. Some older larger 10:1 probes (e.g. Tektronix) use an adjustable moving
capacitance tube and have a much higher rated voltage and are useful for mains
and SMPS and line output work, where the peak pulse voltages can be over 1kV @
50kHz, which most of the smaller probes CAN NOT safely handle! See the rating
curve for your probe...
Peak Volts
700ｴ
600ｴﾄﾄﾄﾄﾄﾄﾄﾄｿ Typical Probe Derating Curve
500ｴ ﾞ
400ｴ ﾝ This means that you can't scope HF Tx aerial!
300ｴ \
200ｴ '�.,__
100ｴ ~~''ﾄﾄﾄ----....,,_______
0ﾅﾄﾄﾄﾄﾂﾄﾄﾄﾄﾂﾄﾄﾄﾄﾂﾄﾄﾄﾄﾂﾄﾄﾄﾄﾂﾄﾄﾄﾄﾂﾄﾄﾄﾄﾂﾄﾄﾄﾄﾂﾄﾄ>Hz
0 50k 100k 200k 500k 1M 2M 5M 10M
1:1/10:1 SWITCHED PROBE
These are also common, with a built in switched attenuator reducing input
loading on 10:1. and the 1:1 option for seeing small signals, but note the
loading changes when switching.
On 10:1 mode, it must be calibrated before use on that scope's input!
PROBE PARTS
Spring Hook ﾞ Tip Probe Adj SW Coax ___
_________/~~~~~~ﾞ _ﾚﾄﾄﾄﾄﾄﾄﾄ||~~~~~~~~ｳﾄ- ｳ~'ﾄ-ｿ___\\ ___ﾚ-ﾄ'~ｳ -ﾄｳ ﾃ'~~ｳｳ
c_\________| ﾞ ﾄｴ_ｳ || 0 _ﾜ ｳｳｳ ｳ ｳ ｳ ｳ ｳｳｳ ｳｳ ｳｳ
\______ﾞ ﾀﾄﾄﾄﾄﾄﾄﾄ||________ｳ-ﾄ ｳ_.-ﾄﾙ~~~~ \\~~ﾀﾄ-._ｳ ﾄ-ｳ___ﾃ.__ｳｳ
ﾞ 1:1:10
Input Probe parts
Load ﾚｴﾃﾄｿC Adj * SCOPE INPUT LOAD
10M�+ ﾄ47Rﾅ9Mﾄﾅ)============================o)ﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾂﾄﾄﾄScope
15pF ｳ_\_ｳｳ 55pF Low capacity 2m lead ｳ �25pF=== 1M Attenuators
or 1M >ﾄﾄﾄﾄﾄﾄﾄﾄﾙ Z = 150R ﾀﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾁﾄﾄﾄ& Amp
+80pF
Usable up to 6-10MHz @ 1:1, & 60MHz @ 10:1. Voltage limited by probe and switch
design/10x scope input or scope input @ 1:1. Due to the added switch and risk
to the scope I would not use this type on any high voltage like mains or SMPSU
testing!
10:1 SCOPE END TRIMMED
These are the less common, with a fixed probe capacitor, the trimmer is put at
the scope end. As it is the scope input capacitance that varies scope input to
scope input, this approach lets the probe maker better match the components
(e.g. series Ls & Rs etc) to get a better frequency/pulse response, however the
probe tip capacitance is a little bit higher!
Must be calibrated before use on that scope's input!
Not able to see very low signal levels.
PROBE PARTS
Spring Hook ﾞ Tip Probe Coax ﾚﾄﾄﾄﾄﾄｿ BNC
_________/~~~~~~ﾞ _ﾚﾄﾄﾄﾄﾄﾄﾄ||~~~~~~ｳﾄ- ｳ~'ﾄ-ｿ___\\ ___ﾚ-ﾄ'~ｳ -ﾄｳ ﾃ'~~ｳｳ
c_\________| ﾞ ﾄｴ_ｳ || ｳｳｳ ｳ ｳ ｳ ｳ ｳｳｳ 0 ｳｳ ｳｳ
\______ﾞ ﾀﾄﾄﾄﾄﾄﾄﾄ||______ｳ-ﾄ ｳ_.-ﾄﾙ~~~~ \\~~ﾀﾄ-._ｳ ﾄ-ｳ Adj ﾃ.__ｳｳ
ﾞ ﾀﾄﾄﾄﾄﾄﾙ
Input Probe parts
Load ﾚｴﾃｿFixed C SCOPE INPUT
10M�+ ﾄ47Rﾁ9Mﾁ)=============================ﾂﾄﾄo)ﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾂﾄﾄﾄScope
15pF >ﾄﾄﾄﾄﾄﾄﾙ 70pF Low capacity 3m lead ﾀﾄｴﾃｴ �25pF=== 1M Attenuator
Z = 150� *Trimmerﾀﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾁﾄﾄﾄ & Amp
The accurate series 9M� gives the 10:1 DC calibration with the scope input R.
The fixed C in the probe has to be exactly 1/9 of the total input capacitance
and the scope end *trimmer is adjusted for this.
Usable DC-100MHz where the loading is not important. Voltage limited to by
probe design/10x scope input, this may be higher than the probe end trimmer
type.
100:1 TRIMMED PROBE
Same as above but are less common, usualy scope end trimmed allowing for high
voltage with the larger in built attenuator reducing input loading by 100,
useful on sensitive large siganl DC or where higher capacity probe can't be
used, if there is enough signal!
No good for low signal levels!
Input Probe parts
Load ﾚｴﾃﾄｿFixed C SCOPE INPUT LOAD
100M� ﾄ47Rﾁ99Mﾁ)==============================ﾂﾄo)ﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾂﾄﾄﾄScope
+4pF >ﾄﾄﾄﾄﾄﾄﾄﾄﾙ 70pF Low capacity 3m lead === ｳ �25pF=== 1M Attenuators
Z = 150R Trimﾀﾄﾄﾁﾄﾄﾄﾄﾄﾁﾄﾄﾁﾄﾄﾄ& Amp
The accurate series 99M gives the 100:1 DC calibration with the scope input R.
The high voltage C in the probe has to be exactly 1/99 of the total input
capacitance for the probe to be flat.
Usable DC-60MHz. Voltage limited to by probe design/100x scope input e.g. 1.5kV
Even so some are not rated for SMPSU work see derating curve above, where the
peak spike voltages may be 1kV @ 50kHz!
10:1 SCOPE & PROBE TRIMMED
These are far less common, with a trimmer capacitor & presets. They give the
best performance and must be calibrated before use on that scope's input!
Not able to see very low signal levels.
PROBE PARTS
Spring Hook ﾞ Tip Probe Coax ﾚﾄﾄﾄﾄﾄﾄﾄｿ BNC
________/~~~~~~ﾞ _ﾚﾄﾄﾄﾄﾄﾄ||~~~~~~ｳﾄ- ｳ~'ﾄ-ｿ__\\ __ﾚ-ﾄ'~ｳ -ﾄｳ ﾃ'~~ｳｳ
c_\_______| ﾞ ﾄｴ_ｳ || 0 Adjｳｳｳ ｳ ｳ ｳ ｳ ｳｳｳ 0 0 0 ｳｳ ｳｳ
\______ﾞ ﾀﾄﾄﾄﾄﾄﾄ||______ｳ-ﾄ ｳ_.-ﾄﾙ~~~ \\~ﾀﾄ-._ｳ ﾄ-ｳ Adj ﾃ.__ｳｳ
ﾞ ﾀﾄﾄﾄﾄﾄﾄﾄﾙ
Input Probe parts 3 HF
Load ﾚｴﾃｿC trimmer 1kHz preset Rs SCOPE INPUT
10M�+ ﾄ47Rﾁ9Mﾁ)============================ﾄR1ﾂﾄﾄﾄﾄﾄo)ﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾂﾄﾄﾄScope
16pF >ﾄﾄﾄﾄﾄﾄﾄﾙ 35pF Low capacity 1.5m lead ﾃR2ﾄｴﾃﾄｴ �25pF=== 1M Attenuator
Z = 150R R3 ｳ ｳ ｳ & Amp
ﾃﾄLﾄﾂｴﾃﾁﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾁﾄﾄﾄ
ﾀ47Rﾙ
Usable DC-300MHz where the loading is not important. Voltage limited to by
probe design/10x scope input. The probe trimmer affects 1kHz and the 3 scope
end presets all affect different HF frequencies allowing good calibration on
square wave harmonics to over 300MHz and a pulse rise time of 1.4nS.
AP BNCs
This a surrounding locking ___ ｱｱｱｱ
pin system that tells the -ﾄｳ ﾃ'~~ｳｳ
scope you have a 1:10 probe ｳｳｳ ｳｳ ｳｳBNC
fitted, for on screen ﾄ-ｳ___ﾃ.__ｳｳ
calibration information etc. ｱｱｱｱﾜﾜPIN
PROBE PARTS INTERCHANGEABILITY
Various makers often use similar parts, but not always! e.g. Tip threads can be
different, and also the tip length and diameter making it incompatible to some
makes of probes hooks.
Screw on leads are also made in slightly different ways and may not be
compatible!
CALIBRATING A SCOPE PROBE *
Connect the probe to the scope 1kHz square wave calibrator and set the input,
trigger and timebase range to show a large square wave. Then using the
insulated tool provided adjust the trimmer...
TO LITTLE HF CORRECT TO MUCH HF
____ _ ______ __ ｳ`\.___
,/' ｳ ,/' | | | | | | | = faint
| | | | | | | | | | Verticals
| | | | | | | | |
| `\.___ｳ | |______| | | ___|
ｳ./'
With a 2 (or more) trimmer probe a higher frequency test square wave of 1MHz
will be needed for the scope end trimmer(s). Adjust the trimmers in much the
same way, endeavouring to get the best square "corner pulse" shape possible.
FAULTY SCOPE ATTENUATOR
If the wave shape changes (other than height) as the scope input attenuator is
changed, then the scope attenuator needs recalibrating, as the input capacity
(& hence the probe response) should not change if the scope is set up OK!
PROBE FAILURE
Tips: These can brake the screw in tip off as there is huge leverage with the
whole probe on the end, but you can get spares with probes.
Hooks: The hook sleeve will melt if left on components while soldering! The
hooks also break, (made of wire or metal strip) due to the leverage factor.
_ _________________________ﾚﾄﾄﾄﾄｿ
(/_/ |\\Spring\\\|ｱｳ ｳ -=Probe
~~~~~~~~~~~~~~~~~~~~~~~~~~~/ﾀﾄﾄﾄﾄﾙ Top
Solder
I have made long lasting replacement hooked strips from scrap junior hacksaw
blades cut into strips and filed out the hook shape with a needle file. A good
solder (try ally solder) and key filing are needed to attached the blade metal!
Body: These fail due to broken internal wires to the socket, and also fractured
PCB. The assembly can be difficult to take apart. but all the plastic covers
are push fit. A broken multiplying R is usually fatal, unless you want a 1:1
probe! Be careful not to lose the red tweaker cover when sliding the hand cover
off. Switched versions need extra care!
Plastic covered _ Handle pulls off >
metal probe tube ｳ ﾀﾄﾄﾄ----..,..
Screw _______________ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ __ Tight push fit socket
on tip -<ｳ- [ heatshrink covered PCB -[ｱ[
~~~~~~~~~~~~~~~ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ ~~\Lead connector screw thread
Earth contact ring/ｳ_ﾚﾄﾄﾄ''''~~~~~
^ Keyway
N.B. Some probes use a metal plated plastic body, so are not metal at all!
FAULTING LEADS
Broken intermittent inner of very thin (hair gauge) lose single core as it will
not stretch, or poor the push on crimped outer connectors. these have just a
centre pin to make connection to the movable inner wire.
Repairing by shorting the lead by too much my uncalibrated it! But with some
patience, these can often be cut back a few cm and reterminated, but which end?
_____
ﾚﾄﾄﾄｿ 10:1===========ｵScopeｳ
ｳHF ｳ / ﾀﾄﾄﾄﾄﾄﾙ
ｳSigﾃﾄ330Rﾄﾁﾄ>===============
ｳGenｳ ｳ bad lead
ﾀﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ
This test circuit will show up which end has is the break, by not dropping the
scope trace level when the centre is connected.
SCOPE BNC: If moulded on type little can be done. Box type these can fail due
to movement of the plug/socket wires to the PCB and although fiddle are easily
repaired.
PROBE PICKUP/HUM LOOPS
With different earth potentials and high capacity from mains filters to chassis
it is quite normal to see unwanted signals on a sensitive range on the scope.
This not helped by long resistive scope leads, so 1st try a thick bonding lead
from the scope earth point to the work (NO LIVE chassis use isolation
transformer).
ﾚﾄﾄﾄﾄﾄﾄﾄｿ
____ ｳ Scope ｳ
ｳWork <ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｴY ｳ
ｳ ｳ ｳ ｳ
ｳ____ｳ================ｳ_______ｳ
Mains earth ﾄﾄﾙ HUM DIFFERENCE ﾀﾄﾄﾄﾄﾄMains Earth
SHORTED OUT
Differential mode can be useful to, where you use both scope inputs to see the
difference..
ﾚﾄﾄﾄﾄﾄﾄﾄﾄｿ
____ ｳ Scope ｳ
ｳWork <ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｴY1\ Diffｳ
ｳ ﾚ<ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｴY2/ Modeｳ
ｳ____ｳ ｳ________ｳ
Mains earth ﾄﾄﾙ HUM DIFFERENCE ﾀﾄﾄﾄﾄﾄMains Earth
For HF noise try the ferrite ring trick on the mains or scope probe lead and
see the common mode noise disappear.
ﾚﾄﾄﾄﾄﾄﾄﾄｿ
___________ ____ ｳ Scope ｳ
ｳ Mains ｳ 2 core ｳWork <ﾄﾄﾄﾄﾄ((((ﾄﾄﾄﾄﾄﾄｴY ｳ
ｳ Isolation ｳ=mains lead=ｳ ｳﾄﾙ ==== ｳ ｳ
ｳTransformerｳ ｳ____ｳ Ferrite ｳ_______ｳ
~~~~~~~~~~~~~ HF noisy PSU ﾀﾄﾄﾄﾄﾄMains Earth
Also see my buls on "Oscilloscopes" & "Scope & DMM Calibrator".
Why Don't U send an interesting Bul?
73 De G8MNY @ GB7CIP
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