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G8MNY > TECH 24.03.09 01:23l 241 Lines 11261 Bytes #999 (0) @ WW
BID : 21324_GB7CIP
Read: GUEST
Subj: Scope Probes
Path: IZ3LSV<IK2XDE<ON4HU<F1ZNR<F4BWT<ON0BEL<ZS0MEE<GB7CIP
Sent: 090323/2303Z @:GB7CIP.#32.GBR.EU #:21324 [Caterham] $:21324_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (New Mar 09)
(8 Bit ASCII Graphics use code page 437 or 850)
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 LOAD
Input o)==============================ÂÄo)ÄÄÄÄÄÄÄÂÄÄÂÄÄÄScope
75/50ê >Ù 75/50ê coax 75/50ê ³ ÷25pF=== 1M Input
TermÀÄÄÁÄÄÄÄÄÄÄÁÄÄÁÄÄÄAttenuators
The scope input capacitance has the minimum effect on the signal.
Only usable on DC-RF 75/50ê 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
& BNC at the scope end. Simple nothing to adjust!
SCOPE LOAD
Input >Ä)================================o)ÄÄÄÄÄÄÄÂÄÄÂÄÄÄScope
1Mê+ >ÄÙ 300pF of lead Capacitance ³ ÷25pF=== 1M Input
325pF e.g. 75ê coax ÀÄÄÄÄÄÄÄÁÄÄÁÄÄÄAttenuators
The capacitance depends on coax impedance & lead length. Only usable on DC AF &
low Z circuits where the loading is not important e.g. DC-3MHz (just about OK
on terminated 75ê 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, but no in built
attenuator or adjustable trimmers. The spring hook can changed to a long probe,
just the tip or be adapted to a BNC plug. Simple nothing to adjust!
PROBE PARTS
Spring Hook Þ Tip Probe Coax ___
_________/~~~~~~Þ _ÚÄÄÄÄÄÄÄ||~~~~~~³Ä- ³~'Ä-¿___\\ ___Ú-Ä'~³ -ij Ã'~~³³
c_\________| Þ Ä´_³ || ³³³ ³ ³ ³ ³ ³³³ ³³ ³³
\______Þ ÀÄÄÄÄÄÄÄ||______³-Ä ³_.-ÄÙ~~~~ \\~~ÀÄ-._³ Ä-³___Ã.__³³
Þ .Ä.__ Screw or Screw or
ÚÄÄÄÄÄ¿ ³ ³ _³ Crimp Crimp BNC
Long Probe Þ ÃÄBNC_³ ³ ³ ³
_________/~~~~~~Þ ÀÄÄÄÄÄÙ ³_³ÄÄÙ
ÜÜ\________| Þ _ Ý Earth
\______Þ /~ ³Tip Þ Clip
Þ \_ ³Shroud Ý
~ Þ
Input Probe parts SCOPE LOAD
Load -----)============================o)ÄÄÄÄÄÄÄÂÄÄÂÄÄÄScope
1Mê+ >ÄÄÄÙ 100pF Low capacity lead ³ ÷25pF=== 1M Input
130pF e.g. 500ê coax ÀÄÄÄÄÄÄÄÁÄÄÁÄÄÄAttenuators
The load capacitance depends on lead length & the coax type which here is a
very fine cored polly foam insulated high impedance type.
Only usable on DC AF & low Z circuits where the loading is not important
e.g. DC up to 6-10MHz on 50ê terminated (25ê) systems.
Voltage limited to scope input. 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/input!
Not able to see very low signal levels.
PROBE PARTS
Spring Hook Þ Tip Probe Coax ___
_________/~~~~~~Þ _ÚÄÄÄÄÄÄÄ||~~~~~~~³Ä- ³~'Ä-¿___\\ ___Ú-Ä'~³ -ij Ã'~~³³
c_\________| Þ Ä´_³ || 0 Adj³³³ ³ ³ ³ ³ ³³³ ³³ ³³
\______Þ ÀÄÄÄÄÄÄÄ||_______³-Ä ³_.-ÄÙ~~~~ \\~~ÀÄ-._³ Ä-³___Ã.__³³
Þ
Input Probe parts
Load ڴÿC Adj * SCOPE LOAD
10Mê+ ÄÁ9MÁ)============================o)ÄÄÄÄÄÄÄÂÄÄÂÄÄÄScope
15pF >ÄÄÄÄÙ 100pF Low capacity lead ³ ÷25pF=== 1M Input
e.g. 500ê coax ÀÄÄÄÄÄÄÄÁÄÄÁÄÄÄAttenuators
The accurate series 9Mê 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 input capacitance
(including the scope capacitance 12-40pF) for the probe's frequency & phase (pulse) response to be flat.
Usable DC-60MHz (3.5nS rise time). Voltage limited to by probe design/10x scope
input. Some older larger 10:1 probes use an adjustable moving capacitance tube
& have a much higher rate voltage & are useful for mains & SMPS work, where the
peak voltages may be up to 1kV & @ 50kHz, which most of the smaller probes can
safely handle! See the rating curve for your probe...
Peak Volts
700´
600´ÄÄÄÄÄÄÄÄ¿ Typical Probe Derating Curve
500´ Þ
400´ Ý This means that you can't scope HF Tx aerial!
300´ \
200´ 'ú.,__
100´ ~~''ÄÄÄ----....,,_______
0ÅÄÄÄÄÂÄÄÄÄÂÄÄÄÄÂÄÄÄÄÂÄÄÄÄÂÄÄÄÄÂÄÄÄÄÂÄÄÄÄÂÄÄ>Hz
0 50k 100k 200k 500k 1M 2M 5M 10M
1:1/10:1 SWITCHED PROBE
These are also common, with a built in switchable attenuator reducing input
loading on 10:1. & 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/input!
PROBE PARTS
Spring Hook Þ Tip Probe Adj SW Coax ___
_________/~~~~~~Þ _ÚÄÄÄÄÄÄÄ||~~~~~~~~³Ä- ³~'Ä-¿___\\ ___Ú-Ä'~³ -ij Ã'~~³³
c_\________| Þ Ä´_³ || 0 _Ü ³³³ ³ ³ ³ ³ ³³³ ³³ ³³
\______Þ ÀÄÄÄÄÄÄÄ||________³-Ä ³_.-ÄÙ~~~~ \\~~ÀÄ-._³ Ä-³___Ã.__³³
Þ 1:1:10
Input Probe parts
Load ÚÄ´ÃÄ¿C Adj * SCOPE LOAD
10Mê+ ÄÅÄ9MÄÅ)===========================o)ÄÄÄÄÄÄÄÂÄÄÂÄÄÄScope
16pF ³_\__³³ 100pF Low capacity lead ³ ÷25pF=== 1M Input
or 1M >ÄÄÄÄÄÄÙ e.g. 500ê coax ÀÄÄÄÄÄÄÄÁÄÄÁÄÄÄAttenuators
+130pF
Usable up to 6-10MHz @ 1:1, & 60MHz @ 10:1. Voltage limited by probe & switch
design/10x scope input or scope input @ 1:1. Due to the added switch & risk to
the scope I would not use this type on any high voltage like mains or SMPSU
testing!
100:1 TRIMMED PROBE
These are the less common, with the larger in built attenuator reducing input
loading by 100, useful on sensitive DC or where higher capacity probe can't be
used, if there is enough signal!
It must be calibrated before use on that scope/input!
No good for low signal levels!
Input Probe parts
Load ÚÄ´ÃÄÄ¿C Adj * SCOPE LOAD
100Mê ÄÁÄ99MÄÁ)===========================o)ÄÄÄÄÄÄÄÂÄÄÂÄÄÄScope
+4pF >ÄÄÄÄÄÄÄÙ 100pF Low capacity lead ³ ÷25pF=== 1M Input
e.g. 500ê coax ÀÄÄÄÄÄÄÄÁÄÄÁÄÄÄAttenuators
The accurate series 99Mê gives the 100:1 DC calibration with the scope input R.
The trimmer C in the probe has to be exactly 1/99 of the total input
capacitance for the probe to be flat.
Usable DC-60MHz where the loading is not important. 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 voltages may be 1kV & @ 50kHz!
10:1 TRIMMED SCOPE END
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/input!
Not able to see very low signal levels.
PROBE PARTS
Spring Hook Þ Tip Probe Coax ÚÄÄÄÄÄ¿ BNC
_________/~~~~~~Þ _ÚÄÄÄÄÄÄÄ||~~~~~~³Ä- ³~'Ä-¿___\\ ___Ú-Ä'~³ -ij Ã'~~³³
c_\________| Þ Ä´_³ || ³³³ ³ ³ ³ ³ ³³³ 0 ³³ ³³
\______Þ ÀÄÄÄÄÄÄÄ||______³-Ä ³_.-ÄÙ~~~~ \\~~ÀÄ-._³ Ä-³ Adj Ã.__³³
Þ ÀÄÄÄÄÄÙ
Input Probe parts
Load ÚÄ´ÃÄ¿Fixed C
10Mê+ ÄÁÄ9MÄÁ)===========================ÂÄÄo)ÄÄÄÄÄÄÄÂÄÄÂÄÄÄScope
15pF >ÄÄÄÄÄÄÙ 100pF Low capacity lead ÀĴô ÷25pF=== 1M Input
e.g. 500ê coax *TrimmerÀÄÄÄÄÄÄÄÁÄÄÁÄÄÄAttenuator
The accurate series 9Mê 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 &
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.
10:1 SCOPE & PROBE TRIMMED
These are far less common, with a trimmer capacitor at both ends. They give the
best performance & must be calibrated before use on that scope/input!
Not able to see very low signal levels.
PROBE PARTS
Spring Hook Þ Tip Probe Coax ÚÄÄÄÄÄÄÄ¿ BNC
________/~~~~~~Þ _ÚÄÄÄÄÄÄ||~~~~~~³Ä- ³~'Ä-¿__\\ __Ú-Ä'~³ -ij Ã'~~³³
c_\_______| Þ Ä´_³ || 0 Adj³³³ ³ ³ ³ ³ ³³³ 0 0 0 ³³ ³³
\______Þ ÀÄÄÄÄÄÄ||______³-Ä ³_.-ÄÙ~~~ \\~ÀÄ-._³ Ä-³ Adj Ã.__³³
Þ ÀÄÄÄÄÄÄÄÙ
Input Probe parts ÚÄ´ÃÄ¿3 HF
Load ÚÄ´ÃÄ¿C trimmer 1kHz R ³Trimmers
10Mê+ ÄÁÄ9MÄÁ)===========================ÅÄÄÄo)ÄÄÄÄÄÄÄÂÄÄÂÄÄÄScope
16pF >ÄÄÄÄÄÄÙ 100pF Low capacity lead ÃRĴô ÷25pF=== 1M Input
e.g. 500ê coax ³ ³ ³ ³
ÀR´ÃÄÁÄÄÄÄÄÄÄÁÄÄÁÄÄÄAttenuator
Usable DC-300MHz where the loading is not important. Voltage limited to by
probe design/10x scope input. The probe trimmer affects 1kHz & the 3 scope end
trimmers all affect different HF frequencies allowing good calibration on
square wave harmonics to 300MHz & a pulse rise time of 1.4nS.
AP BNCs
This a surrounding locking ___ ±±±±
pin system that tells the -ij Ã'~~³³
scope you have a 1:10 probe ³³³ ³³ ³³BNC
fitted, for on screen Ä-³___Ã.__³³
calibration information etc. ±±±±ÜÜPIN
PROBE PARTS INTERCHANGEABILITY
Various makers often use the similar parts, but not always! E.g. Tip threads
can be different, & also the tip length & diameter making it incompatible to
some makes of probes hooks.
Screw on leads are also made in slightly different ways & may no be compatible!
CALIBRATING A SCOPE PROBE *
Connect the probe to the scope 1kHz calibrator & set the input, trigger &
timebase range to show the square wave. Then using the insulated tool provided
adjust the trimmer...
TO LITTLE HF CORRECT TO MUCH HF
____ _ ______ __ ³`\.___
,/' ³ ,/' | | | | | | | = faint
| | | | | | | | | | Verticals
| | | | | | | | |
| `\.___³ | |______| | | ___|
³./'
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, endevering to get the best square "corner pulse" shape possible.
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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