Oscilloscope probes

[Kosmic]

I humbly suggest to new probers, see the Tek concept book series of 1980s
Oscilloscope Probe Circuits, a really excellent overview.

https://www.davmar.org/TE/TekConcepts/TekProbeCircuits.pdf

Finally, Here's a modern Tek note on probes
https://download.tek.com/document/60W_14232_9_MR_Letter.pdf

Interesting read. Thank you for the link.

[jjoonathan]

Thanks for the links and the overview! It's not far off of the "overview from 10,000 feet" that I got years ago and that has served me well. There's  more to say, but it is out of scope for this thread.

However, I think it does all of us a disservice to pretend that the value market doesn't exist. In a professional environment, dropping a few hundred (or a few thousand, or more) dollars on a probe makes sense. Predictability and convenience have a gigantic premium when you're paying a half dozen engineer wages and racing to market. Well-to-do or semi-professional hobbyists such as you and I might also reasonably choose to pay a premium for reliability and convenience. But it is important to respect those who must make do with less. This thread is about helping them, and in this day and age the value options are good enough to deserve their attention.

Case in point: the P6500 we have been talking about. It's a $30 clone of a $500 new / $150 used Tektronix probe. It does the same job as the brand name probe to within a tiny sliver of the performance margin. One of its accessories is unreliable -- but I don't think that accessory is even included with the Tek probe, so you can throw it in the trash bin without upsetting the value calculation. Or hold onto it and remember the caveat. Even if reliability is the concern -- and for a hobbyist, unlike a professional, it might reasonably not be -- the $120 in savings could likely be better invested elsewhere, e.g. in replacing cheap BNC bias tees, which in contrast to the P6500 do a good job of earning the contempt directed at them.

Your caveat about frequency ranges is right on point, though. 10pf of capacitance hits 50 Ohm at 300MHz. Regardless of the brand or lack thereof, it really isn't much of a high impedance probe at that frequency anymore!

[jonpaul]

Hello again

Over the years I Have paid $20...60 for excellent condition Zo and 1 meg 10x Tek probes like the ones I have mentioned.

It takes patience and persistence but you can find bargains on epay.

In my experience its penny wise and pound foolish to buy the cheap Chinese knockoffs.

Just an old timers thoughts!

Happy Probing

Jon

[Dexter2]

Yes, the setup was ok, as you can see the Tektronix probes measure as expected in comparison on the same setup.

My purchased P6500 probe also looks a bit different from what I see from Kosmic pictures. It has a black cable that is also a bit thinner. So, the argument is true, mine are a different knockoff.   I don’t know if there are any additional internal pots for compensation, but I don't want to disassemble it as I want to return it to the seller as they are obviously garbage.

[Dexter2]

I completely agree with you jonpaul. The only time I broken this rule I got kicked in the but with 500Mhz probes that can be used for nothing.

In comparison to expensive but probably the best passive probes from Tektronix I also have good experience with new German probes from TESTEC. They never let me down and only little more expensive than the Chinese probes. the only think i don't like about them as they are a bit bullky like lower priced segment Keysight/R&S pasive probes. But that depends on taste...

[Dexter2]

Another thing. I just measured the capacitance of my P6500 probes and its 14.2pF (advertized as 12pF). So even from this perspective it does not live up to the marketing.

[jonpaul]

Be cautious in measuring small capacitances, like probes!

You need a high measuring frequency, even 10 KHz is not enough for good accuracy.
Stray capacity to ground is an issue.

We use HP and Wayne Kerr bridges at 100kHz-10 MHz and have shields and guards.
A network analyzer is another method.

The handheld digital C meters will not give better than a few pF accuracy

Enjoy

Jon

[Kosmic]

I took the time to run some tests on different probes, and it confirm what Jon is saying.

Part1: https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg2416473/#msg2416473
Part2: https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg2436075/#msg2436075

Tektronix probes are performing a lot better than every Chinese probes I tested.

[Dexter2]

Be cautious in measuring small capacitances, like probes!

You need a high measuring frequency, even 10 KHz is not enough for good accuracy.
Stray capacity to ground is an issue.

We use HP and Wayne Kerr bridges at 100kHz-10 MHz and have shields and guards.
A network analyzer is another method.

The handheld digital C meters will not give better than a few pF accuracy

Hi jonpaul,

I measured with 100Khz on an new Japanise NF ZM2372 with 5V drive voltage and proper open/short compensated probes. Tektronix TPP0500 measured as 4pF (<4pF Specified), P6139B as 8.2pF (8pF specified) so i'm quite confident in the measurement of my P6500 as 14.2pF.

[jonpaul]

Hello all

Very Odd to see probes with more than one compensation adjust.

The Tek 10x probes have a single trim capacitor.

Only current and high voltage probes need more than one.
.
Has anyone ever opened the Chinese or other probe with 2 or more compensation adjustment?

Post a schematic?

Just an interesting question.

Cheers


Jon

[Dexter2]

Hi everyone,

Today I received instructions with pictures from the seller of the P6500 probes how to optimize them. I think the thought was, if I’m not satisfied, I can still return them after the procedure. Disassembly was quite simple, and I must say mine also looks the same inside as the pictures of Kosmic even if the cable is black and thinner. There are two trimm capacitors and 3 potentiometers. The same construction as within the Tektronix P6139B probe.

After about half an hour playing with the settings the probe performs much better. -3db point is at 100Mhz so still no 500Mhz passive probe but better (-6db is actually near 400Mhz…). My performance is no in the range what Kosmic and jjoonathan measured.

Below the old vs new frequency response vs the P6139B probe:


35ps rise time Square wave 10Mhz signal "P6500 received settings" (Yellow is reference)


35ps rise time Square wave 10Mhz signal "P6500 Optimized settings" (Yellow is reference)


35ps rise time Square wave 10Mhz signal "P6500 Optimized settings zoom" (Yellow is reference)


Optimization setup:


Manufacturer optimisation procedure:

Addjust the trimmers in the order of R1->R3->R2 then repeat to obtain optimal response. It helps also to tweek the hi freqency response if you tweek C4.

To sum things up, clones seem to be the same as others on the forum have, it just seems i got a lot with bad internal adjustment. The probes if adjusted can resolve frequencies over 100Mhz and i can not describe them as terrible anymore. Still the usefulness with their high capacitance is limited. Even with an 50ohm source the probe loading is considerable influence over 100Mhz. So in general i would say a 100Mhz probe with extended response:) Its one thing to measure signal generator outputs or pulse generators and another a real circuit.

But then if i compare this to a low cost TPP0250 (250Mhz) Tektronix probe that can be had for 30-50€ if you are patient on eBay and their 3.9pF capacitance this is no comparison. But its a shame the TPP range can be only used on modern Tektronix scopes and the P6139B is their last higher freqency universal one...  I will also do a comparison to German TESTEC HF212 300Mhz probes when i get them. They can be had for 44€ new.

[worsthorse]

Hi there, I am a retired EE, have been collecting, studying and using probes since 1970s, including FET, differential, current and high voltage probes.

I humbly suggest to new probers, see the Tek concept book series of 1980s
Oscilloscope Probe Circuits, a really excellent overview.

https://www.davmar.org/TE/TekConcepts/TekProbeCircuits.pdf

Finally, Here's a modern Tek note on probes
https://download.tek.com/document/60W_14232_9_MR_Letter.pdf

Happy Probing!

Bon journée

Jon (in Paris)

Jon, thanks for this!

Second this... track down the Tektronix concept series notes on oscilloscope and probe circuits. The material is still relevant and will teach you a lot about how oscilloscopes and probes work and interact with circuits!

EDIT: and if you are going to buy one good set of probes, used P6137 price/performance is pretty darn good.

[Kosmic]

Hello all

Very Odd to see probes with more than one compensation adjust.

The Tek 10x probes have a single trim capacitor.

Only current and high voltage probes need more than one.
.
Has anyone ever opened the Chinese or other probe with 2 or more compensation adjustment?

Post a schematic?

Just an interesting question.

Cheers


Jon

Tektronix has a lot of probes where the high frequency adjustment are hidden in the base of the probe. Same as the P6500. But in the manual they normally explain how to do that. In the case of the P6500 it's really not clear that you can open the plastic case.

Ex, high frequency adjustment of the P6134:


Ex, high frequency adjustment of the P6106:

[jonpaul]

Hello all,

Many Thanks for the probe adjustment notes!

I never used the internal tweaks, the single exposed trim always worked fine for me.

Certainly Tek P6137 is one of the best 10x, recommended for Tek 2465/7 series.

Be sure to use the shortest ground clip if pulse or wideband is important.

Happy Probing!

Jon
(from Paris)

[tautech]

The new SP3050A 500 MHz passive probe for the SDS5000X models has 2 HF adjustments in the BNC termination.
https://siglentna-qwavztc8hvq2w.stackpathdns.com/wp-content/uploads/2019/02/SP3025A_3050A_Users_Guide.pdf

[Dexter2]

Very Odd to see probes with more than one compensation adjust.

Has anyone ever opened the Chinese or other probe with 2 or more compensation adjustment?

Post a schematic?

On jon's request the schematic of P6500 compensation. Maybe someone else also finds it interesting...

[exe]

After about half an hour playing with the settings the probe performs much better. -3db point is at 100Mhz so still no 500Mhz passive probe but better (-6db is actually near 400Mhz…). My performance is no in the range what Kosmic and jjoonathan measured.

What's the source impedance?

[Dexter2]

Source impedance is 50ohm (but the signal generator has an ALC level circuit to hold the level). Probes ware connected directly to generator output via direct adapter(no cables) to measure the frequency response.

[starlight_tools]

Looking to get a set of 4 pcs  100X probes for the SDS1104X-E scope that I have ordered.

I have narrowed the selection down to

P4250

Pintek CP-3308R

B&K  PR2000B

Any thoughts on these?

[tautech]

Looking to get a set of 4 pcs  100X probes for the SDS1104X-E scope that I have ordered.

I have narrowed the selection down to

P4250

Pintek CP-3308R

B&K  PR2000B

Any thoughts on these?

The Pinteks are what I've got for stock of 100x probes when I order stuff from them. They're well priced and well enough spec'ed for when you need them.
http://www.pintek.com.tw/files/pintek/CP-3308R-spec.pdf

P4250 OTOH has only a 10M tip impedance according to the manufacturers website and that alone would put me off them. 

BK one looks like the Pintek.

However when working with HV when you want these probes it's good to have a bright red one to remind you you're playing with stuff that bites ! 
Take care and stay safe.

[starlight_tools]

Thanks gang,

Pintek CP-3308R it is, got a confirmation this morning that they have been shipped from Taiwan, estimated delivery of June 6 to the 13th. 

https://www.ebay.ca/itm/2pc-Oscilloscope-Probe-Kit-CP-3308R-100-1-300Mhz-1500V-100M%CE%A9-Readout-Pin-PINTEK/142102785647

Now for the ISFEs, no rush on those as I have to replenish my mad money fund.

On another note, ordered a few sets of DMM leads, 24-in-1 Silicone Cat III 1000V.  I have been looking at the silicone leads due to their high temperature characteristics to connect a DT33C DMM with Temperature measurement to a 1300 deg C K type probe for heat treating metal.    https://www.ebay.ca/itm/232864780778


Walter, TTDr

[worsthorse]

Looking to get a set of 4 pcs  100X probes for the SDS1104X-E scope that I have ordered.

I have narrowed the selection down to

P4250

Pintek CP-3308R

B&K  PR2000B

Any thoughts on these?

The Pinteks are what I've got for stock of 100x probes when I order stuff from them. They're well priced and well enough spec'ed for when you need them.
http://www.pintek.com.tw/files/pintek/CP-3308R-spec.pdf

P4250 OTOH has only a 10M tip impedance according to the manufacturers website and that alone would put me off them. 

BK one looks like the Pintek.

However when working with HV when you want these probes it's good to have a bright red one to remind you you're playing with stuff that bites ! 
Take care and stay safe.

Tautech, are the Pintek probes only available through ebay? Can't seem to find a US distributor...

[tautech]

Dunno wch, surely there's someone over there that can get them.
Google fu should find a supplier.

[starlight_tools]

Found another supplier for Pintek, the price was better than the supplier that listed them on ebay, Globalmedia.com, but they are located in Auckland NZ and payment terms were wire transfer or local bank transfer.

Walter

[worsthorse]

Thanks all. Looks like getting them shipped from TW (and ebay) is my only option.