Home made DMM accuracy check - calibration ..  - Page 1
Forum section: electronics / general

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 07, 2010, 11:33:11 pm
content: I have to point out one amazing for my taste link ..Tips about basic test and calibration tools .http://lategahn.2log.de/index.php?calibration-standards-introductionI got very excited , and ordered all ready the parts for the DC calibrator .Found the major chip in Germany , and I have just buy it ..Now I am looking for resistors ...

author: DJPhil
author_rank: Frequent Contributor
timestamp: July 08, 2010, 01:04:14 am
content: Good find!I bookmarked that one for future reference. Thanks for the heads up.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 08, 2010, 06:55:01 am
content: You are welcome ...Now I am looking for Military Film metal resistors ..And I do have locate my ebay source ...But I do have one question .. is at the film metal resistors .. quality issues ?I find easily offers of 30 or 50 resistors of your choice for few dollars.And I am ready to trust more the VISHAY brand , than no-name ones.Are any better brands than this ?

author: saturation
author_rank: Super Contributor
timestamp: July 08, 2010, 10:36:42 am
content: Be careful about buying parts off eBay or unknown distributors especially based in China, there are a lot of counterfeit electronic parts.Quote from: Kiriakos-GR on July 08, 2010, 06:55:01 am

author: rf-loop
author_rank: Super Contributor
timestamp: July 08, 2010, 01:59:30 pm
content: Quote from: Kiriakos-GR on July 08, 2010, 06:55:01 amVishay is good but can not forget Caddock for precision resistorshttp://www.caddock.com/But Vishay VHP100 series reistors are good (low TC and low ageing)http://www.datasheetcatalog.org/datasheet/vishay/vhp100.pdfmaybe using with cheap 0,02 - 0,05% Voltage reference these are littlebit overkill, but not if try make true lab grade references. (but it is totally different case)-----------------------------------Maybe Vishay have not yet move manufacturing to China... (but many many highly trusted brands are... maybe also we can soon wait Chinese most high brands.Counterfeits... some times (some special) counterfeits are also better than originals.. sometimes value is as waste.btw many chinese ebay etc sellers get components and equipments also from western countries factories production lines... (u want one surplus/waste container or do you want 100. Opening these waste containers may be very "eyes opening surprice")

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 08, 2010, 06:54:52 pm
content: Well I got the decision to start my own High precision decade resistors box.I had on my boxes one nice 10 way selector .And found in China , 0.1 Ohm resistors Vishay Dale..So, soon I will be ready to build the first step of my decade box.The cost of the resistors was an overkill like 15$http://www.vishay.com/docs/30206/lvr.pdfMy plan are the scale 0.1 - 20KAbout the overkill in the tolerance of the resistors , the meters that I would like to check,has an error of 2-3% at the Ohm scales , so I think that anything as resistor at 1% tolerance ,it will do fine.

author: 363616
author_rank: Newbie
timestamp: July 13, 2010, 01:24:38 am
content: One place to get nice components is from surplus high quality measurement equipment. Sometimes the shipping cost can be prohibitive unless you can find the stuff locally. About 8-10 years ago I found a local guy who was selling surplus government equipment out of his garage. One of the things I got from him was an old HP differential voltmeter for $10. It didn't work, but it had lots of good components and hardware when I scrapped it. HP analog meters from their instruments are quite good -- I built a microgram scale from one that worked like a charm. The differential voltmeter had some high quality resistors inside (many of them were matched pairs to 0.01% or better) and stamped with their value, tolerance, and date of manufacture (around 1967 if I remember). One of those resistors is my primary resistance standard, around 1.1 kohms.I also bought from that guy a Fluke 893A differential voltmeter, an instrument I used in the 70's when doing R&D at Varian. This meter probably dates from about the same time and it is dead-nuts accurate and reads exactly the same as my beloved HP3456, another legendary instrument.I also got an Ithaco lock in amp for scrap parts. It was US government surplus and was a gold mine for parts (I think it had 4 or 5 10-turn pots with counter dials in it).

author: northernlight
author_rank: Newbie
timestamp: July 13, 2010, 08:18:06 pm
content: Hi everyone,I'm currently building a voltage reference too. My thought was to be able to test the 2V or 4V and 20V or 40V DC range. So I found the AD REF195 with 5V +- 2 mV for the higher range. For the lower range I'm between the LM4140 with 1,024 V @0,1%, 10ppm/°C and the ones with 3 or 6ppm/°C. The tolerance of the reference voltage is influenced by the tolerance of the supply voltage. A 7812 has got usually 5%. So I'm using a LP2951ACN @ about 6,5V for the AD REF195 and a LP 2950 CZ3,0 (behind the 2951) for the LM4140 (Uin max 5,6V). They have a tolerance of 0,5%. Voltage regulators work better with a little load, so I'm putting a LED @10mA behind the 2951 and a 3k resistor behind the 2950. A diode in +Uin and a Transil at Uin and both Uref complete the design.For resistors I'm going with 0,1% from Yageo. I simply use 4mm sockets and solder the resistors (10/100/1k/10k/100k/1M) connected between them. Since many of my DMM are rated 1% in ohms and my best DMM at 0,15%, that is good enough.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 13, 2010, 08:46:06 pm
content: Quote from: 363616 on July 13, 2010, 01:24:38 amFound another source ...How about aircraft switches for military use ..I am Crazy I know that ..Just got 6 of those ... (payed and they will be shipped tomorrow from US )Got a better price as lot of 6 , but I can not publish it ..http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=140206409746About Janco ...http://www.esterline.com/controlsystems/JANCO/JANCOHome/tabid/2474/Default.aspxI am going to do an ultimate quality Decade resistors Box , even looking for only 15ppm 0.1% resistors.Its very hard to locate the components , but I am trying , at list I found the selectors,and the 0.1 Ohm resistors .Now I have on targetthe Electronic Project Box .. and some of the needed values of resistors.

author: Unknown
author_rank: Unknown
timestamp: July 13, 2010, 09:11:28 pm
content: If you're going for best accuracy, make sure to provide Kelvin connections, which is especially important for the low resistors (eg. 0.1 ohm), otherwise you might as well not go through all that trouble. You would need double pole rotary switches for that. This only helps for meters that can do four-wire resistance measurements, but (almost) any high-precision meter supports that.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 14, 2010, 01:04:20 am
content: Well the ones that I got as minimum are 0.1 = 0.10 mOhmsFound the the same resistors as 0.01 so those must be the absolute 1mOhmSo , sorry for the misinformation.Before seconds I got all the rest , minus the 1R , that looks that the seller does not have an listing or stock.In few hours I will know more .. as I am waiting for his message, and to combine shipping.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 14, 2010, 01:11:37 am
content: By the way I need some help ... how do you call in English this type of box .Give me as many descriptions as possible .. Thanks.

author: EEVblog
author_rank: Unknown
timestamp: July 14, 2010, 01:37:43 am
content: Quote from: Kiriakos-GR on July 14, 2010, 01:11:37 amTypically that would be a "sloping desktop console"They are 3 key words I'd use, but there are almost certainly others.Dave.

author: Zad
author_rank: Super Contributor
timestamp: July 14, 2010, 02:42:38 am
content: Definitely a Desk Console case.http://www.maplin.co.uk/Module.aspx?ModuleNo=1693Don't forget, so long as component ageing isn't a huge issue, and you have access tosomethingthat is calibrated, you can use standard components and calibrate many of the errors out with trimmers.

author: DJPhil
author_rank: Frequent Contributor
timestamp: July 14, 2010, 02:42:51 am
content: Quote from: EEVblog on July 14, 2010, 01:37:43 amExactly.Here's a few links to some examples from Hammond.Themain enclosure pagehas pdf catalog links at the bottom for various worldwide distribution chains.1456 Series-SECM Series-500/515/519 SeriesHope that helps.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 14, 2010, 10:47:19 am
content: Thanks for the Help people ..The market are full of truly nice products ...The one at the right , the woody one took my hart .. and gave me ideas..At the place that I work , they had an German Decade ,the box was made only for hard plastic ..Something that bothers me , are if the box should be isolated "full plastic" ,or with aluminum front mask ..I need to stay away of any issues , caused by the contact of the Rotary Switch's axle .Because everything will be connected in series.( By the way all above resistors are Vishay ones )And the seller has run out of 1R ones ....

author: Rhythmtech
author_rank: Regular Contributor
timestamp: July 14, 2010, 08:05:10 pm
content: Woody was definitely the way to go!

author: jimmc
author_rank: Frequent Contributor
timestamp: July 14, 2010, 10:31:43 pm
content: I'm a bit worried about those switches, with a contact rating of 5 Amps @ 28vdc, the contacts are likely to be a silver alloy of some form.This may give problems when used in a 'dry' circuit i.e. little or no voltage / current; for switching such circuits gold contacts are more reliable but will have a maximum current rating measured in mA.seehttp://www.allaboutcircuits.com/vol_4/chpt_4/2.htmlfor detailsExtract:With all this discussion concerning the reduction of switch contact arcing, one might be led to think that less current is always better for a mechanical switch. This, however, is not necessarily so. It has been found that a small amount of periodic arcing can actually be good for the switch contacts, because it keeps the contact faces free from small amounts of dirt and corrosion. If a mechanical switch contact is operated with too little current, the contacts will tend to accumulate excessive resistance and may fail prematurely! This minimum amount of electric current necessary to keep a mechanical switch contact in good health is called the wetting current.Normally, a switch's wetting current rating is far below its maximum current rating, and well below its normal operating current load in a properly designed system. However, there are applications where a mechanical switch contact may be required to routinely handle currents below normal wetting current limits (for instance, if a mechanical selector switch needs to open or close a digital logic or analog electronic circuit where the current value is extremely small). In these applications, is it highly recommended that gold-plated switch contacts be specified. Gold is a "noble" metal and does not corrode as other metals will. Such contacts have extremely low wetting current requirements as a result. Normal silver or copper alloy contacts will not provide reliable operation if used in such low-current service!Using 0.1 Ohm resistors is problematic there is no way that you will be able to get better than around 10% accuracy without using a 4 terminal technique.seehttp://www.allaboutcircuits.com/vol_1/chpt_8/9.htmlWith 6 switches in series the total contact resistance will be well over 100 mOhm!To get an idea of a commercial decade box seehttp://www.allaboutcircuits.com/vol_1/chpt_8/9.htmlnote the residual resistance is specified as less than 0.25 OhmI would certainly use a metal case, connecting the case to earth will reduce interference pick-up significantly. With a maximum resistance of 1.1111 MOhm the insulation resistance of the switch contacts to the mounting bush should not be a problem (>>1000 MOhm)Jim

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 14, 2010, 11:45:53 pm
content: Jim I truly appreciate all the effort that you did , for all those details .My friend@almdid wrote about ...QuoteFew messages above ,and by searching I did found the same sources .About the switches they have an contact resistor as 0.002 / end of life max 0.020 Ohm .I am going nuts because I can not find any 1R 0.1% tolerance on Ebay .I will have to use 1R 1% ...About the box, I have on my scope one very large one,so to add 7 switches + 6 stand alone standard values of resistors + 10V DC calibration module.So , other than Decade box , it would be an DMM tester in " large scale "More info soon , as soon I will have lock my targets , as Box and pointing knobs .There is no room now to step back , this is a costly project , and I have pay the 60% of the total cost.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 16, 2010, 12:25:46 am
content: Got my knobs today ... about 10 of them ..The best that I could find ... ( Taiwan )

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 16, 2010, 08:37:39 pm
content: Ok my shopping basket become full , got it all ..One last detail stands in the way ,Zero Ohm resistors ( connection link 0.010 Ohm )oror silver plated copper wire !!If some one has a preference , just say it , and justify it ..Thanks .

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 17, 2010, 10:25:55 am
content: Hmm ok , solve that too.Just ordered silver plated copper 1mm 1M long ,and ANTEX special solder with silver ..QuoteThats it .. now I will start planning , the position of the parts at the face plate ..link from the box ...http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=390216247453As about the 1R resistors, I found only 1R 1% 1/4W , well got them too. ( 50 of those , price per pack )

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 18, 2010, 05:07:32 pm
content: Just did another weird "buy " ..If the resistor box , its just the beginning in the principal of testing multimeters ,this one that I got, its the next step ..QuotePDFhttp://www.timeelectronics.com/download/1030v1c.pdfPricing in the UShttp://easthillsinstruments.com/electrical/electrical-source/time-electronics-1030-microcal-voltage-current-source.htmlMy ebay Pricehttp://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=280535080797My price 31 EUR shipped ..Home pagehttp://www.timeelectronics.com/1030-Voltage-and-Current-Source.htmlPricing in UK as 320 pounds..The left one.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 19, 2010, 01:56:48 pm
content: DALE 0.1 Ohm .... arrival .. Spot on.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 22, 2010, 01:26:09 pm
content: I will probably start an new thread, about my new project" Home made PRO Decade box ".But I can not hide my excitement , from the arrival of the special switches.They came today , and it's one little box, hides one very seriously packaging ...Box + soft paper towel + air sealed bag + mini bag .The main contact looks Gold plated .Looks really luxurious and high quality ..

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 30, 2010, 11:21:31 pm
content: Portable calibrator in action .........