Capacitance and Inductance Standards specifications - Muirhead - Page 1
Forum section: electronics / general

author: KirstyA
author_rank: Contributor
timestamp: February 24, 2023, 07:29:19 pm
content: Hi Everybody,I recently bought some old Muirhead inductance and capacitance standards but can't find any specifications on them.Just wondering if anybody has any information on them.I'm primarily interested in:-For the Inductors - specification tolerance, temperature drift and current handling.For the Capacitors - specification tolerance, temperature drift and voltage rating.Any other parameters, like frequency range, also welcome.I have tested all the capacitors and they appear to be very accurate, as long as you have the guard/shield strap in place.I have looked hard to find any information on these but to no avail.If anybody has information on these it would be much appreciated, thank you.Muirhead Decade InductanceType A-517-A 10x 0.1mHType A-517-B 10x 1mHType A-517-C 10x 0.01HType A-517-D 10x 0.1HMuirhead Mica CondenserType B-517-A 0.001µFType B-517-A 0.005µFType B-517-A 0.01µFType B-517-A 0.05µFType B-517-A 0.1µFType B-517-A 0.2µFType B-517-B 0.5µFType B-517-C 1.0µFMuirhead Decade CondenserType B-21-F 3 decade box 10x 0.1, 10x 0.01, 10x 0.001 uFIncrementally adjusted Residual 0.000150uF (150pF)

author: TimFox
author_rank: Super Contributor
timestamp: February 24, 2023, 07:44:43 pm
content: You might be able to find the specifications for similar General Radio units online: I would guess the Muirhead specs are roughly similar.See pages 56ff and 62ff of this 1939 catalog:https://www.ietlabs.com/pdf/GR_Catalog/GenRad_CatK1_1939.pdfThe IET website has quite a few of the classic General Radio catalogs online.

author: KirstyA
author_rank: Contributor
timestamp: February 24, 2023, 10:43:30 pm
content: Hi Tim,I have downloaded that catalogue, thank you.On page 57 there are type 505 condensers, silver mica construction, encased in wax, in bakelite cases. This is exactly like the Muirhead ones, so I think it likely the spec is very similiar.They are classed as Secondary Laboratory Standards. That sounds about right to me for these.Nothing in the catalogue about decade inductors. Maybe General Radio have another catalogue with those in.Thanks for your help.Kirsty

author: TimFox
author_rank: Super Contributor
timestamp: February 24, 2023, 11:32:00 pm
content: Go to the IET website and look for postwar G-R catalogs.

author: trobbins
author_rank: Frequent Contributor
timestamp: February 25, 2023, 04:53:01 am
content: Worldradiohistory.com allows searching of UK magazines etc (eg. WW) and that can identify Muirhead lab gear references.

author: lowimpedance
author_rank: Super Contributor
timestamp: February 27, 2023, 01:07:27 am
content: Quote from: KirstyA on February 24, 2023, 07:29:19 pmThe only information I have is from old catalogues and I have scanned and attached FYI.

author: trobbins
author_rank: Frequent Contributor
timestamp: February 27, 2023, 05:24:07 am
content: The higher value tapped inductors may include a magnetic core. I have Sullivan air core secondary standards for 10uH and 100uH, and a GR 1mH (of about the same size as that Muirhead brochure).The 10uH and 100uH are fixed, and appear to have a nominal 1% accuracy, based on 10.5 and 99uH 'actual' markings. So it would seem that 1% tolerance was nominal back then, They still measure at their nominal inductance.I have not attempted to measure their tempco, but would anticipate the 10u and 100u would be low based on the construction and choice of materials used. They have .41 and 1.1 ohm DCR's, which would limit their current capability. The GR is 2.1 ohm DCR and in two wound sections to rotate relative to each other to final inductance, so heating may well need to be limited to just a few watt.

author: KirstyA
author_rank: Contributor
timestamp: February 27, 2023, 07:43:55 pm
content: lowimpedancewhat anABSOLUTE HEROyou areTHANK YOU so much for taking the time and trouble to look for your old catalogues and scan all of these items at high quality.It is Very Much appreciated.I think you are likely the only one who has info on old Muirhead equipment like this. There is nothing I could find anywhere on the Internet, and I did look hard.Once your info is gone, I think that will be itI am gradually building up my own set of Standards in order to eventually be able to calibrate my own equipment.It won't be to certified lab standards but more than good enough to maintain my own equipment and these standard capacitors are better than I imagined and most defintely what you would class as Laboratory Secondary Standards.Kirsty

author: KirstyA
author_rank: Contributor
timestamp: February 27, 2023, 08:06:52 pm
content: trobbins, thank you for that insight.According to the info provided from lowZ's Muirhead catalogues the inductance units are adjusted to 5% and shipped with certificates of 1% of each step.I didn't get any certificates so I have to accept them as being 5% tolerance until I can either have them calibrated or hire a suitable LCR meter and do it myself.I also have a single Sullivan-Griffiths 1uH inductor that I got off eBay.I found this old advert giving some technical information on it, see photo.

author: trobbins
author_rank: Frequent Contributor
timestamp: February 28, 2023, 12:19:59 am
content: Kirsty tanks for that Sullivan-Griffiths info - I have a slightly different style/variant, as per attached photo from internet.May 1933 Wireless Engineer has an article on your temp-comp style of inductor, which may have then morphed in to the commercial product I have.As another measurement approach, I have used the impedance measurement capability of REW software and a soundcard to cross-compare the factory stated value of my 99uH Sullivan-Griffith inductor along with a BR2822 RLC meter with circa 0.3% tolerance (but uncal) which measured from 99uH at 100Hz, 99.4uH at 1kHz and 99.09uH at 10kHz.

author: KirstyA
author_rank: Contributor
timestamp: March 01, 2023, 02:12:34 pm
content: trobbinsthat is interesting. I have just set up a computer in my workshop as a dedicated piece of test equipment for GPIB/IEEE, old Eprom programmers, audio measurements and anything else it could be useful for. I have a very good studio quality sound card in there.What is the 'REW' software and how did you set up the soundcard with the LCR meter? Sounds interesting.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: March 01, 2023, 04:19:37 pm
content: You might also consider Visual Analyserhttps://www.sillanumsoft.org/This has a full feature LCr meter section.I have a few old GR inductance standards that are (I think) good to 0.1%. They typically sell for too much and hardly anybody cares about low frequency inductance anymore. Somewhere I have an article on winding a DIY standards using accurate dimensions. It's surprising how good you can do. Also have a 1632 inductance bridge, but haven't used it for quite a few years. Remember that inductors are the least pure impedance we have!

author: KirstyA
author_rank: Contributor
timestamp: March 01, 2023, 08:03:27 pm
content: Conrad Hoffmanthanks for the info on that software.I would be interested in that article about winding your own standards if you can find it?

author: trobbins
author_rank: Frequent Contributor
timestamp: March 01, 2023, 11:26:43 pm
content: Kirsty, REW is Room Equalisation Wizard as it started as software for audio system assessment, but has shown its usefulness for a wider variety of audio and instrumentation applications. Link below to its support forum, which includes a sticky to software download. It now has widespread use by audio community due to its continual improvement and support by its designer (feature improvement can be quite rapid to cover user needs), and it is freeware on many operating platforms, and the ubiquitous availability of high quality soundcards as the hardware tool - an example of one of many threads is linked below. It has an impedance measurement tool as a speaker impedance and modelling suite, which has the ability to model inductors and capacitors. The REW help page link below shows the method. A few google searches will show up many threads on people setting up those measurements, and I even had REW help with measuring down to 0.1Hz when assessing iron-core chokes, and I also used it for cross-comparing capacitor accuracy - link below - to the point of measuring the frequency accuracy of my soundcard.https://www.avnirvana.com/forums/official-rew-room-eq-wizard-support-forum.10/https://www.diyaudio.com/community/threads/how-to-distortion-measurements-with-rew.338511/https://www.roomeqwizard.com/help/help_en-GB/html/impedancemeasurement.htmlhttps://www.eevblog.com/forum/metrology/diy-capacitance-measurement-using-simple-rc-bridge-based-technique/

author: KirstyA
author_rank: Contributor
timestamp: March 02, 2023, 02:22:07 pm
content: trobbinsthanks for those useful links. There is some very interesting stuff in those links, including your own post in the last link.I need to have a good read of your EEVBlog post. Never considered using a soundcard for Capacitance measurements or anything of that nature.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: March 05, 2023, 03:46:13 pm
content: Quote from: KirstyA on March 01, 2023, 08:03:27 pmI need to search the archives, some of which are not terribly accessible right now, but give me a bit.