DCCTs (Ultrastab for example): Infos and working/defective devices sought - Page 1
Forum section: electronics / general

author: Echo88
author_rank: Frequent Contributor
timestamp: March 31, 2020, 05:52:25 pm
content: At the moment im trying to understand Direct Current Comparator Transducers like the LEM Ultrastab-series in detail, which led me to buy some different used ones and study the relevant papers about the Fluxgate-technique.I stripped the toroid in a defective Danfysik 867 to better understand them and am at reverse-engineering the schematic.Id also like to study the more elusive and expensive ones, like the higher and much lower amperage Ultrastab-variants: IN 2000-S or the ITN 12-P for example.There are other manufacturers too like DaniSense and Hioki which produce such DCCTs, but their devices dont appear on ebay.So, if someone here works with those and could share teardown-photos or even lend/sell me one of those mentioned devices, id be very happy to analyze them also.Apparently the DCCTs can get destroyed by applying primary current without powering the supply rails first, so im hoping that maybe out there are some defective ones which could be bought and analyzed, before they are thrown away?In the end all that gathered knowledge is planned to be released as an xdevs-article, which includes pictures/measured testpoint-waveforms/schematic/etc.I know that lymex wanted to do a similar analysis some years ago, but apparently he didnt continue this project.Also related is his usage of DCCTs to build current sources:http://bbs.1ppm.cn/topic/54/%E9%87%87%E7%94%A8it-600-s%E7%9A%84%E6%A8%A1%E5%9D%97%E5%8C%96%E9%AB%98%E7%A8%B3%E5%AE%9A30a%E7%94%B5%E6%B5%81%E6%BA%90-10a-60a-modular-design-of-highly-stable-30a-current-source-by-using-lem-it-600-shttp://www.alliantech.com/pdf/capteurs_courant/867-200I.pdfhttps://www.danisense.com/images/pdf/0-600A/DS400ID.pdfhttps://www.hioki.com/en/products/detail/?product_key=6504https://www.lem.com/sites/default/files/products_datasheets/itn_12-p.pdfhttps://www.lem.com/sites/default/files/products_datasheets/in_2000-s_ultrastab.pdf

author: chuckb
author_rank: Frequent Contributor
timestamp: May 09, 2020, 03:00:49 am
content: I evaluated the current noise performance of the Ultrastab 867-600 several years ago. With no current in the core, it had 8uapp measurement noise with a 350 ohm (or 3500 ohm) burden resistor.The temperature stability with zero current was very good also.Someone on bbs38 had a schematic but I can't find it now.Good luck with your testing.

author: JohnG
author_rank: Frequent Contributor
timestamp: May 11, 2020, 01:38:33 pm
content: I am interested in this topic, since I have a couple of the Ultrastab 867-600 that I use for work, and a broken one as well, which I would like to fix. By broken, there is a ferrite core inside the case with a broken top half (RM core, IIRC).As I recall, later models have some protection against damage due to sending current through the core without powering the device. It would be interesting to know if the fix is as simple as degaussing the core, or did they also change core material or add circuit protection to prevent degaussing from damaging other parts of the device.Cheers,John

author: Echo88
author_rank: Frequent Contributor
timestamp: May 11, 2020, 06:24:47 pm
content: Afaik theres no 867-600. Do you mean 866-600?If you can state the correct device name and maybe make a photo of the pcb and place of damage, i can most likely give you the correct schematic (i have both) and we can see if its repairable.So far i assume you mean the Transformer T1 or the inductivity L2 in the 866-600.If the wiring isnt destroyed it should be possible to swap the N48-ferrite-cores and maybe some OPs to get it working again.Edit: They did change the core-design in later models and also slightly changed the schematic.Degaussing shouldnt be necessary as thats included in the offset-spec of the device (earth magnetic field, self magnetization, etc.) i think.

author: chuckb
author_rank: Frequent Contributor
timestamp: May 11, 2020, 09:34:36 pm
content: I had my model number wrong. It's an 867-700I, a 700 amp sensor.

author: JohnG
author_rank: Frequent Contributor
timestamp: May 12, 2020, 03:24:32 am
content: Quote from: Echo88 on May 11, 2020, 06:24:47 pmYou are correct. It is an Ultrastab 866, rated for 600 A max. It was the transformer that had a cracked core, labeled T1 on the PCB silk screen. Pieces were missing, which means someone else had opened it up or they would have been inside the case. I happened to have an R400 core that fit (in photo), but I did not power it up since I had no schematics, and I had a working one that was suitable for my current calibration setup.Any help appreciated!John

author: Echo88
author_rank: Frequent Contributor
timestamp: May 12, 2020, 06:07:23 pm
content: The schematic, which was made my lymex, is attached.The schematic differs from the real 866 in the following: instead of the two 2N2222 it uses a 75453 Driver:https://www.ti.com/lit/ds/symlink/sn75453b.pdf?&ts=1589305928796and instead of the DG303 a DG403 is used.You need N48 cores if you want to repair L2 or T1.A bit theory:The square wave from the LMC555 drives the Detector Windings "Det" of the toroid via L2 and T1. If magnetic flux in the toroid isnt exactly zero, then 2. harmonic peak voltages are generated by the excitation windings.Those voltages are demodulated by the DG403, then filtered and supplied to the feedback-loop consisting of the OP-amps.The Pickup coil "Comp" (which is the wrong name in the schematic) extends the frequency range of the DCCT by acting as a rogowski-coil."MagHead" is the compensation winding, which compensates the magnetic flux in the toroid via LM675T and burden-resistor Rm.Current consumption of the 866 should usually be around 200mA positive and 30mA negative afair.Tell me if you have more questions.

author: JohnG
author_rank: Frequent Contributor
timestamp: May 14, 2020, 01:39:20 pm
content: Thanks, highly appreciated. I do have some questions and assumptions, so I'm looking for correction, confirmation, etc.I am assuming Rm (2.5 ohm) is the burden or sense resistor.The maghead shows one of the CT windings connected to ground at the CT only. Is it an electrostatic shield, or something else missing a connection?I have just found what I think is the correct the replacement core half at Mouser (https://www.mouser.com/ProductDetail/EPCOS-TDK/B65807N0315A048?qs=sGAEpiMZZMs2JV%252BnT%2FvX8Isth6XFmTokiQ%252BGA%2F4ge14%3D) and Digikey (https://www.digikey.com/product-detail/en/tdk-electronics-inc/B65807N0315A048/495-75211-ND/3914138). It was not available when I last checked (> 4 years ago). I have just ordered a few.Cheers,John

author: Echo88
author_rank: Frequent Contributor
timestamp: May 14, 2020, 06:02:02 pm
content: Yes, Rm 2.5R is the burden/sense resistor.I dont know why lymex has drawn the compensation winding "MagHead" this way, since the compensation winding is usually wound as just two separate coils, which are then connected in series on the pcb at the DSUB-connector to get the high number of 1500 turns.The 866-core itself isnt connected to ground as far as i recall.The more recent 867 that i took apart has a different core construction, which has a coppertape-shielded core thats connects to the circuit ground.

author: JimmyJo
author_rank: Contributor
timestamp: May 21, 2020, 12:53:56 pm
content: This document seems useful? no affiliation just found it while searching for DCCT related articles.https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&ved=2ahUKEwi0laPY_8TpAhXB7eAKHb-oC_kQFjAEegQIBRAB&url=http%3A%2F%2F1531356.s21d-1.faiusrd.com%2F0%2FABUIABA9GAAgnqSlyQUoiKGrmAY%3Ff%3D2017%2B-%2BDCCT.pdf%26v%3D1495880223&usg=AOvVaw2oLGeYz6UsabV9fgEv97GQ