Why are Deskew Fixtures expensive? - Page 1
Forum section: electronics / testgear

author: kerouanton
author_rank: Regular Contributor
timestamp: September 05, 2023, 09:11:49 am
content: Now that I have both a differential probe and a current probe from Micsig, I'm looking about the Power Analysis features of scopes and am wondering why Deskew Fixtures are expensive, as they look quite simple in design. As I'm a Siglent user I've looked for their fixture and saw on the forum that in order to calibrate those Micsig probes I have, the PCB has to be cut/adapted, and even so I believe it's overpriced.After looking around, I realized all A-brands seem to sell "raw PCB" fixture devices, which look cheap but are very expensive (oh, by the way, why are all those devices sold as a simple PCB without any case? Doesn't look professional imho, but there must be a reason I don't really catch.On Aliexpress I also researched for cheaper "clones", supposing some manufacturers there may have the idea of designing cheap ones but I didn't find any. That's puzzling for me too, why aren't any chinese manufacturer selling that? (after all they design and sell a ton of crap boards, this one shouldn't be difficult to make either).I remember that there was at least one company in the Netherlands or Belgium that had created a homemade fixture but my memory is deficient and I can't recall the name of the website, I just think it was a long time ago (when I didn't guess what it was meant for) and they stopped selling it. Oh, it's probably Ashlabs, my memory came back... but they seem not to sell the fixture any morehttps://shop.ashlabs.be/I'd love to buy one of the Ashlabs ones, but the thread doesn't seem to have any recent posts.https://www.eevblog.com/forum/testgear/scope-probe-deskew-fixture-pcb-project/msg3168766/#msg3168766

author: tautech
author_rank: Super Contributor
timestamp: September 05, 2023, 09:29:12 am
content: You can use any fast edge for deskewing current probes however a known amplitude pulse is useful for setting current probe attenuation correctly.Follow the thread you linked .......

author: kerouanton
author_rank: Regular Contributor
timestamp: September 05, 2023, 04:10:11 pm
content: That's what I had guessed but I wasn't sure. So as I own a SDG6052X, I could also generate such pulses with it to deskew the probe signals, is my guess good?Nevertheless, thank you for your answer @tautechm, but it doesn't explain the huge price and the fact that they are bare pcb not even in nice plastic boxes ;-)PS:Just ordered another SDS1104X-E today as replacement for my failed one... Having just one scope isn't the best configuration to probe the issues on a failed scope! I contacted Siglent via my local distributor and checked the Service Manual but it seems there can only be a psu, motherboard or screen replacement. So I ordered a new one with a quite nice discount from siglent.eu (I know it's not the official site, just a distributor!).

author: tautech
author_rank: Super Contributor
timestamp: September 05, 2023, 07:45:13 pm
content: Quote from: kerouanton on September 05, 2023, 04:10:11 pmCertainly, SDG6000X can produce edges ~40x faster than the Siglent Deskew PCB ~80ns edge.However the high current pulse/loop produces a current pulse higher than SDG6000X can provide.Spend more time studying the thread you linked.QuoteCough, you mean the one you broke:https://www.eevblog.com/forum/repair/siglent-sds1204x-e-flexible-printed-cable-j12-connector-pn/

author: Martin72
author_rank: Super Contributor
timestamp: September 05, 2023, 09:17:03 pm
content: QuoteAnd that will probably be the reason why the available devices are so "expensive".There are simply no purchasable alternatives to them.I had bought the deskew fixture from siglent, drew a schematic of it and posted it on the forum, that might have caused one or the other replica.I would stick to it in your place instead of buying an "original", especially since the original is not mechanically optimally designed and you have to edit them to be able to clamp narrower current clamps there.

author: kerouanton
author_rank: Regular Contributor
timestamp: September 05, 2023, 10:17:13 pm
content: Quote from: tautech on September 05, 2023, 07:45:13 pmYes, indeed... I still don't know what happened with the ribbon cable anywayI'll assume that's my fault yes!And for the fixture, I'll read back the thread, I promise

author: pdenisowski
author_rank: Super Contributor
timestamp: September 05, 2023, 11:44:35 pm
content: Quote from: kerouanton on September 05, 2023, 09:11:49 amDefine "expensive"Relative to the cost of the scope or relative to the cost of a current probe?Quote from: kerouanton on September 05, 2023, 09:11:49 amWell, our deskew fixture (RT-ZF20) actually does come in a very nice hinged plastic case with molded cut-outs, etc. It's at least as nice a case as our expensive probes come in.To be honest, adding an enclosure to it would make it difficult to clamp the current probes around the openings and attach hooked/pin type voltage probes. Our fixture does have legs so it's not just lying on the bench.And as some of you may have guessed, I also made a video about it a few months ago

author: pdenisowski
author_rank: Super Contributor
timestamp: September 05, 2023, 11:48:32 pm
content: Quote from: tautech on September 05, 2023, 09:29:12 amYou need a fast edge where the voltage and current areprecisely in phase. That's not an easy thing to do at high frequency.It may not matter much if you're simply calculating the power factor of some consumer electronic device, but when you're making measurements of an SMPS with a high switching frequency, having very carefully deskewed probes is worth the cost of the fixture.

author: tautech
author_rank: Super Contributor
timestamp: September 06, 2023, 12:38:02 am
content: Quote from: pdenisowski on September 05, 2023, 11:48:32 pmDefine HF.What frequency does your R&S deskew fixture offer ?

author: slugrustle
author_rank: Frequent Contributor
timestamp: September 06, 2023, 01:59:34 am
content: Gathering from this thread that deskew fixtures are a low sales volume product that needs to be built to somewhat high engineering specifications. Makes sense that they're expensive...

author: pdenisowski
author_rank: Super Contributor
timestamp: September 06, 2023, 09:12:26 am
content: Quote from: tautech on September 06, 2023, 12:38:02 amTouchéQuote from: tautech on September 06, 2023, 12:38:02 amWe spec it as rise/fall times and amplitudes: see attachedhttps://scdn.rohde-schwarz.com/ur/pws/dl_downloads/dl_common_library/dl_brochures_and_datasheets/pdf_1/RT-ZFxx_dat-sw_en_3606-7653-22_v1000.pdf

author: tautech
author_rank: Super Contributor
timestamp: September 06, 2023, 08:12:15 pm
content: Thanks for that.Seems R&S also have a small loop too large for the 100 MHz Tek P6022 current probe, just like with Siglent DF2001A Deskew Fixture.Had to modify mine by removing the PCB loop and fit a wire link to meet the P6022 0.140" max cable dia spec.

author: Martin72
author_rank: Super Contributor
timestamp: September 06, 2023, 08:41:17 pm
content: QuoteAnd I had copied this "Tautech mod", plus an acrylic bottom plate..

author: tautech
author_rank: Super Contributor
timestamp: September 07, 2023, 07:27:34 am
content: Quote from: Martin72 on September 06, 2023, 08:41:17 pmTell me Martin, is the large loop running the same ~22kHz frequency as the small loop ?I've never checked....as I don't have a large/monster current probe.Oh hang on, I measured both the risetimes here:https://www.eevblog.com/forum/testgear/scope-probe-deskew-fixture-pcb-project/msg3169004/#msg3169004

author: kerouanton
author_rank: Regular Contributor
timestamp: September 08, 2023, 10:56:15 am
content: Quote from: pdenisowski on September 05, 2023, 11:44:35 pmThanks for the explanation about your RT-ZF20 fixture, and for the video you made.The RT-ZF20 looks nice but yes for me (hobby usage) it's not in my budget. What I meant by "expensive" was about the price of raw components, no FPGA or MCU, just a NE555 and a MOSFET.Quote from: pdenisowski on September 05, 2023, 11:44:35 pmYes, I like your videos in general, I always learn something.BTW, I went to an automation fair in Bern yesterday and was able to see some MXO4 and other nice SA at the Rohde&Schwarz booth. I may be interested in the RTB2K-COM4 as I found a nice discount (well still quite expensive compared to Siglent for my small budget, but I'm quite tempted).

author: pdenisowski
author_rank: Super Contributor
timestamp: September 08, 2023, 03:26:03 pm
content: Quote from: kerouanton on September 08, 2023, 10:56:15 amThanks! And frankly, I learn a lot while I'm making those videos as well

author: Kean
author_rank: Unknown
timestamp: September 10, 2023, 10:12:20 am
content: Just for reference, I contacted AshLabs in Belgium and they hope to have a small batch available for sale on their website soon...

author: kerouanton
author_rank: Regular Contributor
timestamp: September 14, 2023, 07:47:15 pm
content: Quote from: Kean on September 10, 2023, 10:12:20 amIndeed, and I just ordered one. The product page is therehttps://shop.ashlabs.be/products/current-deskew.Really the 3D-printed cases make the product feel very nice too, and the specs look good. Can't wait to get it soon, I sent it to a friend abroad to "escape" those insane customs taxes...

author: pdenisowski
author_rank: Super Contributor
timestamp: September 14, 2023, 08:19:52 pm
content: Quote from: kerouanton on September 14, 2023, 07:47:15 pmI like the fact that they're demonstrating them using one of our RTM series oscilloscopes

author: Ribster
author_rank: Frequent Contributor
timestamp: September 18, 2023, 07:44:53 pm
content: So lovely to read the comments for the product.I have 1 left in stock, and am preparing a first batch of 20.I actually ordered 200 pcs, so supply will be more dan sufficient from this time on