Author Topic: Decade resistance box re-prupose to DIY 10:1 and 100:1 transfer divider  (Read 11439 times)

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Offline VintageNut

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Re: Decade resistance box re-prupose to DIY 10:1 and 100:1 transfer divider
« Reply #25 on: October 06, 2016, 01:36:20 am »
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For a permanent installation into a cabinet, I think I will borrow a Fluke configuration that is used in their 732B 10V reference. They have small PCB rotary switches that have fixed resistors. You can call it a PCB mounted decade box. You can insert a screwdriver increase or decrease the decade of resistance that you want to dial-in. It is a very clever idea. No more noisy potentiometer wipers.

I have to go find a suitable PCB switch for this purpose. The other option is to mount some surplus KVD or deacde box switches on the front panel and use those.



  Nice approach, why not 1234 configuration decade resistors? with a 16 pdip switch package and 8 resistors you'd have 2 full decades, with times 2 resistors you could avoid having twice the same value and have an 8bit (non volatile) programable resistor, which for what you are telling should be enough to do the job. I guess you are using el cheapo resistors for this as the stability wouldn't matter much for those...

  I've have a 32bit converter coming and I'm trying to figure out how to do a decent decade divider, even buying a nice vishay (assuming I can get one to arrive here) would be a pain to characterize, I could have access to a decent lab at the university but not for too much time, I could get a few references from them to say. I could bring my voltage reference and a few resistors and them tell me the value for a reference temperature, then I would have to find the way around.

JS

I took a look at a couple of binary resistance box projects. Nice idea. I think that I want to go from 0.01 ohms to 1.0 ohms. So, I will need 0.01, 0.02, 0.04, 0.08, 0.16. 0.32, 0.64. The very low resistance values are probably going to be hand wound wire around a large value resistor. Adding a 0.005 to the bottom fills out the8 positions and gives a finer granularity. This "pot" would span 0.005 ohms to 1.275 ohms with a resolution of 0.005 ohms.

I made a 0.01 ohm resistor recently just to do it. It was a fairly short piece of insulated solid copper wire twisted to minimize inductance and shoved into to banana plugs which allows using a DMM force and sense plugs to tweak it. I used it to look at voltage burden of various ranges of a Sourcemeter.

I think that the latest greatest vishay resistors with guaranteed low tempco in a shielded box will probably suffice for a good divider to check your converter. Give it a try and see.
working instruments :Keithley 260,261,2750,7708, 2000 (calibrated), 2015, 236, 237, 238, 147, 220,  Rigol DG1032  PAR Model 128 Lock-In amplifier, Fluke 332A, Gen Res 4107 KVD, 4107D KVD, Fluke 731B X2 (calibrated), Fluke 5450A (calibrated)
 

Offline VintageNut

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Re: Decade resistance box re-prupose to DIY 10:1 and 100:1 transfer divider
« Reply #26 on: October 22, 2016, 02:23:23 pm »
The Fluke 752A has a 100:10:1 divider, and the lower sections are adjustable.   This was done this way so that a (more or less) exact division ratio can be created.  If the temperature in the lab changes a few degrees, you have to re-adjust it.  There is another way to use this Hamon divider-- and that is with no adjustments.  In this case, the ratios are *close* to 1:10 or 1:100, but maybe not exact, and that's OK-- as long as you *know* what the ratio *is* you can still use the divider to measure decade ratios.

This idea, I believe, is the winner.

After some weeks of researching the Datron 4902(S) and the Measurements International 8000B and the articles from the developers of the MI8000B, it looks to me that a mixture of these approaches may be very good for a DIY divider that can be used to rival the performance of the Fluke 752A and the 720A for use in a DIY home lab for precision divided voltages.

A stack of nominally accurate resistors that can be calibrated quickly and accurately every time the divider is used seems to me to be the most practical implementation.

Adjustment pots in the Datron 4902S and the switches in the MI8000B are the sources of difficulty and error.

What I do like is the procedure to perform an automated measurement of each element of the resistor stack before and after every use of the divider.

Here is what I am thinking of building

1. A 3-decade resistor stack. 10 pcs of 1K + 9 pcs of 10K + 9 pcs of 100k. No switches and no pots. Every step of every decade is brought out to a binding post for use as a calibrated voltage for a null meter connection. The top of the stack will be nomianally 1M ohm and calibrated at 1000V. So the voltages will span 1000V to 1V with 28 total cardinal points.

2. System for automated measurement of every position of every decade. This will be a Keithley DMM that accepts switch cards or a Keithley 7001 switch system. I own each and will have to find the correct switch cards to perform the switching and measurements. It will depend on the cost of the cards.

3. voltage sources for energizing the divider and for comparing the decade steps. Fluke 731B for the 10V and 1V step comparison voltages. Maybe the Fluke 332A for the 100V step comparison voltage. For divider energizing, maybe a Keithley 237. The model 237 can force current or can force voltage up to 1000VDC.

The idea is to use what I have in my lab now except for acquiring the correct switch cards.
This is all just paper design right now. Any suggestions are welcomed.

working instruments :Keithley 260,261,2750,7708, 2000 (calibrated), 2015, 236, 237, 238, 147, 220,  Rigol DG1032  PAR Model 128 Lock-In amplifier, Fluke 332A, Gen Res 4107 KVD, 4107D KVD, Fluke 731B X2 (calibrated), Fluke 5450A (calibrated)
 

Offline cellularmitosis

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Hi vintagenut, and progress on this idea?
LTZs: KX FX MX CX PX Frank A9 QX
 

Offline MegaVolt

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Re: Decade resistance box re-prupose to DIY 10:1 and 100:1 transfer divider
« Reply #28 on: September 06, 2019, 02:20:04 pm »
After some weeks of researching the Measurements International 8000B
Do you have any information about the 8000B internals?
 


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