Author Topic: What leads and probes you use and where to get them.  (Read 4756 times)

Offline PekkaNF

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What leads and probes you use and where to get them.
« on: January 15, 2016, 06:58:05 AM »
I have a mötley collection of various 4 mm plug test leads and then some scope probes.

Much of the economy crocodile leads and cheap versions of IC clips and wire probes are crap.

Hirschmann kleps seems to work and has endured. I'm going to order a set or two.

This sort of stuff would be traditional low voltage "kit":
https://www.conrad.de/de/messleitungs-set-lamellenstecker-4-mm-lamellenstecker-4-mm-100-m-schwarz-rot-sks-hirschmann-pms-4-co-120030.html?sc.ref=Category%20Overview

And it offers great flexibility, but:
* I have always been a big fan of 4 mm system, can use all leads together
* Does 2 mm system offers anything else, but smaller current rating and smaller size?

I then realized that I basically have no good probe between standard low frequency multi meter leads and 10Mhz or above oscilloscope probes.

I will construct few specialized measurement probes, that upper frequency will be in region of 200 KHz (some very low volt and some 300-500V) region. Both will be very different from start on.

For low volts there is probably a lot of choices, like:
https://www.conrad.de/de/abgreifklemme-steckanschluss-064-mm-cat-i-weiss-sks-hirschmann-kleps-064-pch-129029.html

But are there any of that type with flying leads or connector that I can easily solder other end of the PCB. There are some mixed quality BNC/test clips, but BNC is a bit bulky and I'm having hard time finding soldered terminals + they are really more suited for coaxial cable.

I like the JST and other that type connectors, they are slimline etc. and outside is insulated. Only problem is that the crimpping plier is pretty expensive.

Suggestions for normal less than 30 VAC low volt measurements and then 230-400 VAC high voltage measurements. They will be completely different probes though.

Pekka


Offline John Swift

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Re: What leads and probes you use and where to get them.
« Reply #1 on: January 15, 2016, 08:08:58 AM »
Hi Pekka

I think its inevitable we end up with large collection of test leads
the kits you have linked to are a good start , I have started off with similar ready made  test leads 
over time I have added various shrouded test leads and DIY leads with 4mm shutter plugs

  John








Offline awemawson

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Re: What leads and probes you use and where to get them.
« Reply #2 on: January 15, 2016, 08:39:05 AM »
Good quality oscilloscope leads are good from DC to several hundreds of Mhz so I'm surprised you are giving a 10 Mhz lower limit on your probes.

Most 'scopes have input switching between DC coupled and AC coupled with the same probe doing both. A decent probe will have a compensation capacitor that is tweakable to get decent rising edges, and a x1 / x10 switch on it
Andrew Mawson
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Offline PekkaNF

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Re: What leads and probes you use and where to get them.
« Reply #3 on: January 15, 2016, 03:17:39 PM »
Scope probes are no problem, they seem to multiply.

Much of commercial stuff is very expensive, because it is over specsed for high rise times, high voltages, low parasitic capacitance and CMRR and all that.

First order of matters: low voltage differentials and such.
I like this type of probes:
https://www.buerklin.com/en/catalog/Test-equipment-sets-type-Hirschmann-T-M-PMS-0-64-F706100.html

Wonder how long the test leads can be left and at what cost in terms of noise and frequency?

I don't like the 4 mm plug at the end of the test lead. Small connector to PCB would be nice. Suggestions?

Good suggestions on BNC connectors that can be soldered on PCB?

High voltage is a different battle. I like the shrouded connectors John brought up. Have some that sort of stuff for Fluke.

Pekka

Offline PekkaNF

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Re: What leads and probes you use and where to get them.
« Reply #4 on: January 17, 2016, 06:01:57 AM »
Bit more search and head scratching...twisted pair gets pretty far on frequency domain, bit more search and I found this one:
http://www.bitscope.com/product/DP01/

Now this is a low cost possibility: Reel of CAT5 cable, little soldering and crimpping and custom probe is ready to go.

+ cheap
+ available and economical connectors are available

- cat cable is a bit stiff and probably not too kind on small IC probes
- cat cable pair does not bend well repeatedly and it is stiff
- cat cable pair will put strain on connector, should find alernative 2 pin connector

Am I on the right track or are there better alternative to DC...way under 1MHz signals shot probe leads?

Any suggestions CAT cable conector that is not ethernet type connector. 2,5 mm or 0,1" spacing is prefered, so is latching body, something like pin strip PCB mount type. I like crimpping connectors, but on this size crimpping pliers are really expensiven. I end up buying connectors as a pigtail, but that is not very common with twisted pair.

Pekka

Offline awemawson

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Re: What leads and probes you use and where to get them.
« Reply #5 on: January 17, 2016, 08:01:00 AM »
CAT 5 comes in two varieties. One for fixed wiring which is solid conductors. The other with stranded conductors suitable for patch leads - this is the type you need if you choose to go the CAT 5 route. (There is also a variety of super flexible CAT 5 but it's pricey.)
Andrew Mawson
East Sussex

Offline PekkaNF

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Offline PekkaNF

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Re: What leads and probes you use and where to get them.
« Reply #7 on: January 31, 2016, 03:53:42 PM »
I like this type connectors (THT; XH; 250V; 3A):
http://www.tme.eu/en/details/b2b-xh-a/raster-signal-connectors-250mm/jst/

http://www.tme.eu/en/details/xhp-2/raster-signal-connectors-250mm/jst/#
+ pig leads
http://www.tme.eu/en/details/sxh-200bk22/raster-signal-connectors-250mm/jst/

Pins are nice too, but I have't found economical crimper for them.

Pekka

I 'think' I found economical crimpper plier to these pins....let's see when it arrives. Really starting to like these JST connectors.

Pekka

Offline PekkaNF

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Re: What leads and probes you use and where to get them.
« Reply #8 on: February 03, 2016, 04:05:03 AM »
Now the questions at the other end of the probe.

The more I read, the more I get confused. I have huge gap in my knowledge. I don't get this termination business...

What I'm missing?

My scope has normal input stage: 1MΩ± 2%, the input capacity is 18pF± 3pF) and connector is normal BNC.

I know that the "standard" connection is 50Ω cables and terminals, tees and all that stuff that goes in to BNC.

I know that scope probes use special cabe and the whole shebang is not that standards 50Ω stuff after all, specaially when it gets into higher frequency.

I'm thinkking of constructing something like this:
http://www.dgkelectronics.com/high-voltage-differential-probe/

(I would be perfectly fine with lower frequency/rise time stuff and really would like something that has lead trough and not SMD)

Most of the stuff I understand to to certain degree there. He choose not to use FET input stage to raise the input impedance and that fits me too.

But the output stage beats me....this 50Ω business again.

Another thing is that do I need the BNC connector there? If I just want coax out, could I terminate the cable right on the PCB and how much art is there? I imagine that the core is soldered and shield is clamped over the copper a little further back.

Could I make one quick and dirty probe and use pigtail + BNC from the old 1:1 or 1:10 probe? Or I'm better of with RG-174 + BNC?

If I'm making the some one-time fixtures, how much active probe amplifier output stage, cable, termination and such changes when -3dB measurement system frequency is at 200 KHz, 1MHz, 10 MHZ or 100MHz?

I feel really dumb at this point. I know classic small signal/small frequency electronics and I know that when frequency grows, new players will show up.

I used to read something about transmission lines, but I haven't learn rule of thumb when one approach is chosen and then next and when something will do and when not on this measurement system. Must have fallen asleep when that was being hammered in our brains.

Pekka

Offline PekkaNF

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Re: What leads and probes you use and where to get them.
« Reply #9 on: February 04, 2016, 03:30:49 AM »
I think I found an obtuse approach angle to this problem:
1) At low frequency passive probe system is largely an resistive network. I.E. voltage divider:
https://cdn.sparkfun.com/assets/3/7/4/7/3/52f3bddece395f19378b4567.png

2) At higher frequency passive probe system is largely LC network:
http://www.emcesd.com/1ghzprob.htm

3) Trouble is what is "low" and what is "high"? I found one rule of thumb: standing wave. Have to look at it when cable length approaches 1/10 wave length....1m of cable somewhere 20-30Mhz?

Now, I think third point assumes something, like sinusoidal signal? How would that translate to rise time?

I did read before that normal passive probe cable has higher resistance than you might expect. Should measure it to find out how to use ebay specials.

Looks also like there is no magic in connector termination or PCB termination under 10-20 MHz. Interesting. Still haven't found all the answers, but building a little confidence that even if I lack complete knowledge I have a little faith that I can do it it and it might even work good enough.

Pekka

Offline PekkaNF

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Re: What leads and probes you use and where to get them.
« Reply #10 on: February 17, 2016, 02:21:52 PM »
I 'think' I found economical crimpper plier to these pins....let's see when it arrives. Really starting to like these JST connectors.

Pekka

Got this plier home and it seems to work, first one I stripped too long.
http://www.ebay.com/itm/321383053381




Offline PekkaNF

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Re: What leads and probes you use and where to get them.
« Reply #11 on: February 26, 2016, 05:08:20 PM »
And got cheap signal geneator up to 24MHz to check if the connectors/cables/termations are any good for the speed.

Since I don't have BNC-T (for termination) and BNC/BNC straight cables I gobled up BNC/terminal to two 100ohm 2W power resistors....some inductance for sure....That should be good up to few MHz.

Now: Never have done any BNC cables and all seem to have crimp connections. Should I have buy cables readily terminated and cut them if shorter pieces are needed?

Where to buy few 50 ohm BNC cables to hook up signal generator/Scope and measurement rig?

Pekka

Offline PK

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Re: What leads and probes you use and where to get them.
« Reply #12 on: February 26, 2016, 06:49:14 PM »
There are a few screw together BNC cable options. They're not as robust as a crimp though...

Offline PekkaNF

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Re: What leads and probes you use and where to get them.
« Reply #13 on: February 28, 2016, 09:44:12 AM »
Like some F-connectors? Novel.

I bought some readymade 50 ohm BNC/BNC cables, terminators and BNC-T:s just need to wait them to arrive and then I can test if the chinese ones I got are 50 ohm or something else.

I need to buy some 2 mm PCB test jacks (sockets?) and maching plugs. I like that safetyplug style, but it would limit suppliers and pretty much to Hirschmann. Which I don't mind if I'll get KLEPS1 size test hooks and set w/ cables on reasonable price, but googling hasn't revealed too much yet.

Pekka