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AOIP RD6 C1: Unusual decade resistance box configuration

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jnd:
Recently I bought two decade resistance boxes on local auction site. The first is usual two terminal + ground but this one has more connections. I have been thinking about use of these additional terminals and haven't found any benefit of those. When using the left side only with R1 and R2 terminals, it's the usual configuration. Then C1 and C2 are the ends of the two largest value decades. Perhaps for some kind of voltage divider, but not too precise one? And the last P terminal is at strange place.

Picture of configuration is attached as well as two of the whole decade from the auction.

Any explanation or suggestion is welcome.

BTW it just arrived today, I have yet to check the values with more accurate meters at work. Also interesting thing is that the box has label from Bohunice (Slovakia) Nuclear Power Plant.

Wartex:
other side is a comparator

I bet it uses 4 resistors per decade, and a dual 11-position rotary switch with 1x,2x,3x and 6x value resistors.

amspire:
A very nice 0.03% decade box. There should be nothing inaccurate using the divider. It uses the 100 ohms decade for the low end of the divider. Apply the input voltage between R1 and R2. Read the voltages between C1 and C2 (the total voltage), C1 and P (for the high side divider voltage) and P and C2 (low side divider voltage) with a DMM with 10 megohms input resistance or better. Many top end multimeter have over 1G input resistance for ranges of 20V or less, and so the resistance between R1 and C1 has negligible effect. With a 10meg meter, you can correct for the voltage loss.

From the switch resistance, I assume it uses silver contacts. Before you test the accuracy turn each switch 10 times from end to end to clean the contacts.

The actual purpose of this box it to simulate platinum PT100 and PT1000 resistive temperature sensors, but it is a perfectly good resistance box regardless.

Richard.

jnd:

--- Quote from: amspire on April 13, 2012, 03:48:31 am ---There should be nothing inaccurate using the divider.

--- End quote ---

I meant when used as divider, the lower half is pretty coarse. I guess the rest of the decade has enough range to adjust finely. So only downside in this mode is varying input resistance which can get quite low.

I'll take it to work at Monday and check how it is looking inside, will take some photos. The other resistance box which I bought earlier is similar to this, six decade Danbridge, 0.03%, with calibration label to 1/2014 (not specified when it was calibrated), only defect is the last decade plastic knob is broken but no electrical problem. The contacts on switches seems to be in good condition and there are 6 wired in parallel (I'll take photo of that too). For $16 with shipping, I think that was incredible deal, especially for this local auction, it's kinda hard to come by some good quality equipment here.

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