Author Topic: Best way for Decade Resistor  (Read 16050 times)

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Offline Nuno_pt

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Best way for Decade Resistor
« on: September 06, 2016, 11:19:22 pm »
Hi all,

This is my first try with Metrology, I'm looking at getting an Decade Resistance standard, to check/Cal my DMM till 6.5 digits.

What would be the best way, buy an GR or ESI decade to 100K or 1M, or build one with VHP101/2z till 100K,  or maybe Caddock TF020/50N till 10M?

I'm thinking about 100 Ohm, 1K, 10K, 100K, 1M, 10M and 100M as values.

I've look at topics from zlymex, TiN, and some others.

« Last Edit: September 07, 2016, 12:18:17 am by Nuno_pt »
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Offline TiN

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Re: Best way for Decade Resistor
« Reply #1 on: September 06, 2016, 11:51:50 pm »
With either way you go, you will be dependent on resistance measurement from calibrated instrument.
So you need define what is best for you (cost? accuracy? stability?) and then pick solution which meets needed requirements.

Also there is high chance that vendor calibration of your 6.5d meter be cheaper than getting resistance standard suitable for such verification.
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Offline Nuno_pt

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Re: Best way for Decade Resistor
« Reply #2 on: September 07, 2016, 12:15:53 am »
Thanks TiN,

Well about the cost of CAL, here they say that the cost would be around 450€ + 23%VAT = 553.50€ for 6.5d meter.
I would think that something in the range of cost vs accuracy vs stability, should be enough.
My first gold was to check if the 2000 is good.

The GR or ESI are around $130 on bay.

I know I still need someone with an Cal DMM above 6.5d to check the Decade, that is the most difficult here since that here most of the people are not involve in Volt-nut, even with Time-nuts only a hand full in the country, so Volt is even worse.


I've a friend that is working on VitrOhm factory here in Portugal (near my house), I know that they have Precision Decades there inside of a control room, Temp & Humi, maybe I should ask him if they have something also for VDC + IDC, and if he could calibrate it there.
Since my 2000 can only be adjust V + I + Ohm.
« Last Edit: September 07, 2016, 12:20:11 am by Nuno_pt »
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Offline zlymex

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Re: Best way for Decade Resistor
« Reply #3 on: September 07, 2016, 12:24:48 am »
One way is to make simple DIY and have someone calibrated unofficially like these photos.

Edit: I've calibrated(unofficially) many resistance and voltage standards here in China, and one of my 10k standard has traveled for two years among R-nuts.
« Last Edit: September 07, 2016, 12:42:03 am by zlymex »
 
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Offline Nuno_pt

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Re: Best way for Decade Resistor
« Reply #4 on: September 07, 2016, 12:29:37 am »
Thanks zlymex,

that was what I was thinking about, making some DIY with the Vishay or Caddock, and see if I can find someone with a 7.5d or maybe an 3458 to read them, and that way I could check my DMM's or maybe CAL them.

The worst still is find some 3457 or 58 in PT, or someone interest in help , to CAL them unofficially.
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Offline ebclr

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Re: Best way for Decade Resistor
« Reply #6 on: September 07, 2016, 12:45:09 am »
 

Offline MosherIV

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Re: Best way for Decade Resistor
« Reply #7 on: September 07, 2016, 12:52:18 am »
Hi

I am in the same/similar predicament as Nuno_pt, I have just got a 6.5 digit meter but is is showing difference between my 5.5 digit meter.
How do I verify which one is in calibration?

I did not think resistance was the way to go, I thought Voltage would be the better thing to concentrat on.
Would I be better off doing the same as Nuno_pt ?
 

Offline zlymex

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Re: Best way for Decade Resistor
« Reply #8 on: September 07, 2016, 12:55:25 am »
Source for military resistors

https://world.taobao.com/item/15143277363.htm?spm=a312a.7728556.2015080705.20.i4CZ0j&id=15143277363&scm=1007.12006.39884.i39005537941&pvid=472a1c7c-3c9b-450d-b14b-d6b6a4a520c2
My first 10V standard(>9 years ago) employ 14 those RX70 resistors for statistical step-up, but proved to be not very good.
Those resistors are made of Manganin with not so small TCR and the drift is not so small too.
 
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Offline zlymex

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Online Vgkid

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Re: Best way for Decade Resistor
« Reply #10 on: September 07, 2016, 01:23:39 am »
here is a spec sheet for those RX-to series resistors. TC is not very good.
http://www.doublecircle.com/doc_down/200908041016185853.pdf
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Offline MosherIV

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Re: Best way for Decade Resistor
« Reply #11 on: September 07, 2016, 01:51:33 am »
Quote
here is a spec sheet for those RX-to series resistors. TC is not very good.
Not surprising. Military Spec is for
a) robustness, both physical and electrical
b) wide temperature range (but not necessarily good temperature stability)
They are also not necessarily good precision.
 

Offline Nuno_pt

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Re: Best way for Decade Resistor
« Reply #12 on: September 07, 2016, 03:02:56 am »
I've to find a place to ask for a quote of:
Vishay 101 for 100 Ohm, 1K, 10K, 100K and VHP202Z for 1 Ohm, 10 Ohm.
For 1M, 10M and 100M, I'm thinking about Caddock  TF020R/N or TF050R/N.

This will all be put in an Alu box, in 4W with some Pomona banana plugs, with an BME280 sensor inside, and some silica bags.

The Alu box would be put inside of an IP67 Plastic box, this box will have 4W connected to the inside bananas trough some CAT5 cable, solder to the outside bananas and connected to the inside bananas with some copper lugs.

Would this be acceptable?
 
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Offline TiN

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Re: Best way for Decade Resistor
« Reply #13 on: September 07, 2016, 03:14:35 am »
Why the plastic box? That makes all bulky without visible benefits, also adding connection points which have more chance to go bad.

Also if you go 4W up to 100K, that will be 24 connectors just for those six resistors, if you want wire them separately.
for 1M and higher, 2W is ok, but insulation become critical there, so you might want to put those ports on teflon sheet or similar.

Good idea for BME280, easy to interface and small footprint to log data. Perhaps also add EEPROM I2C ROM on same board, so one with Pi can store calibration values/environment data/dates on it too ;).
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Offline Nuno_pt

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Re: Best way for Decade Resistor
« Reply #14 on: September 07, 2016, 05:04:57 am »
Thanks TiN, I haven't made the math on the connectors before writhe that, now I see the stupidity of that.

So what about 4W till 100K, and separate box for 1M till 100M with 2W.

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Offline Alex Nikitin

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Re: Best way for Decade Resistor
« Reply #15 on: September 07, 2016, 06:10:23 am »
I am planning to build something similar for my home lab (to calibrate my two Keithley 2015 meters). My current idea is to use a single box with a temperature sensor (and possibly even temperature control) for all resistors and connect each resistor to a 9-pin D socket, eight pins for a 4-wire connection (4 pairs) and the remaining pin for the case/ground/guard. This way I can easily select one of the resistors by plugging the cable (9-pin plug to 4+1 banana plugs) in one of the sockets. The whole unit could be quite portable. I have some nice LT450/C wirewound resistors (0.002%, 3ppm/C) that I might use for that purpose.

Cheers

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Offline Nuno_pt

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Re: Best way for Decade Resistor
« Reply #16 on: September 07, 2016, 06:34:41 am »
I've send an email to Bedex in Germany asking about the prices of VHP101 and VHP202Z, I'll let you guys know if they give some prices.
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Offline Nuno_pt

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Re: Best way for Decade Resistor
« Reply #17 on: September 07, 2016, 07:44:46 am »
i was looking at this video here < >, and thinking if this would be a good road?

I was looking at Caddock TF or USF370 for 1M, 10M and 5x20M for 100M.

Can you explain why the 9 instead of 10 (e.g. 9 Ohm instead of 10).

My 2000 need to be check at 100 Ohm, 1K, 10K, 100K, 1M, 10M, 100M, and for CAL 1K, 10K, 100K, 1M.





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Online Vgkid

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Re: Best way for Decade Resistor
« Reply #18 on: September 07, 2016, 07:54:16 am »
Since this is related what about using the Omega OSW series of switches to select the resistor. In their most simple form, they offer switches with 2,3,4 poles. Even when using the 2 pole arrangement you can have the sense/source binding post wired to the switch. That way you only need 4 binding post. These switches are meant for thermocouples/rtd's/thermistors, so they are offered in either gold/silver plated contacts.
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Offline Macbeth

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Re: Best way for Decade Resistor
« Reply #19 on: September 07, 2016, 08:08:19 am »
How do the modern calibrators work for resistance? Surely they aren't as old school cool as EEVBlog #544 - Fluke 5450A?


I'm guessing with precise voltage and current sources and a micro you can emulate DC calibration resistors all you want and accurately too?

Of course I have tried messing with my CR on my Maynuo DC load and, yeah not quite precision!  :-DD
 

Offline zlymex

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Re: Best way for Decade Resistor
« Reply #20 on: September 07, 2016, 01:03:46 pm »
I had three 5450A. I'm planning to tear one down and get rid of those relays, solder those resistors directly to binding posts.
I had another plan to parallel-series connect the 90k string of deck A inside one of my 720A to get a 10k, but proved to be not very stable.
 

Offline MosherIV

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Re: Best way for Decade Resistor
« Reply #21 on: September 07, 2016, 07:20:59 pm »
Thanks to everyone who gave information.  :-+

I do not have access to anything better than the 6.5 digit meter that I have  :(

I also do not have enough equipment to build such a stablised, precision 10V ref  :-[

I am not too bothered about knowing how imprecise the 5.5 and 6.5 digit meters are at the moment, just (re)learning about metrology.
Oh well  :)
 

Offline Alex Nikitin

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Re: Best way for Decade Resistor
« Reply #22 on: September 07, 2016, 07:33:25 pm »
Thanks to everyone who gave information.  :-+

I do not have access to anything better than the 6.5 digit meter that I have  :(

I also do not have enough equipment to build such a stablised, precision 10V ref  :-[

I am not too bothered about knowing how imprecise the 5.5 and 6.5 digit meters are at the moment, just (re)learning about metrology.
Oh well  :)

Where are you in the UK? Perhaps I can lend you one of my 10V references, measured by HP 3458A Opt 002 and stable to about 5ppm for last 6 months or so (including the HP meter drift). It is small and can easily be sent by Special Delivery if you are not local. Drop me a PM if you are interested.

Cheers

Alex
 

Offline MosherIV

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Re: Best way for Decade Resistor
« Reply #23 on: September 07, 2016, 10:27:09 pm »
Thank you Alex Nikitin, that is a kind offer but I think I will be content with what I have right now.

I know everything is accurate enough to 10mV (thanks to my new Keysight U1232a and UT61E).
Anything beyond that is just a fun learning exercise for me  ;)

FYI, I am in  Milton Keynes
 

Offline MosherIV

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Re: Best way for Decade Resistor
« Reply #24 on: September 08, 2016, 02:58:15 am »
Hi

Some good news (for me at least). I popped in to see the equipment manager where I work and he is allowing me to use the calibrated 6.5 digit meters to verify my AD584. I will then have the confidence in my voltage reference to check against my 5.5 and 6.5 digit meters.

Thanks again to all for the information and offer of help  :-+
 


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