Siemens B2086 Decade Resistor: Calibration

I briefly mentioned the Siemens B2086 Decade Resistor in the previous post. In this post I want to provide additional information on this interesting “vintage” unit, which seems to be geared towards AC application, not just DC.

I couldn’t find a date code on it. However, back in the day they published proper manuals including part lists and schematics (yes!). Those are from 1975 to 1981, so it could very well be 30+ years old.

Here is an excerpt of the electrical characteristics specified in the manual:

CharacteristicsValue
Frequency range\(0\) to \(500 kHz\)
Range\(0.2 \Omega … 999.999 k\Omega\)
Steps\(100 k\Omega\), \(10 k\Omega\), \(1 k\Omega\)
Uncertainty\(\pm F \pm 80 m\Omega + n \cdot 6 m\Omega\)
with
\(F = \begin{cases}0.15\% & 100 k\Omega, 10k\Omega, 1k\Omega, 100 \Omega, \\ 0.35\% & 10 \Omega \\ 1.5\% & 1\Omega \end{cases}\)
\(n\): sum of the digits of the selected resistance
Additional changes at high frequencies
Temperature coefficientDecades \(R \ge 10\Omega\): \(\pm 50 ppm/K\),
Decade \(R < 10\Omega\): \(\pm 300 ppm/K\)
Power rating\(0.5 W\)
Switching voltage\(\le 100V \simeq\)
Switching current\(\le 0.5A \simeq\)
Excerpt of the specs of the B2086 Decade Resistor. I deliberately skipped many of the specs more relevant for AC applications.

All decades use metal film resistors, five of the six decades (probably the upper ones) have hermetically sealed resistors. Siemens used pretty much the same topology as my programmable decade resistor. It does look way more complicated with the rotary switches though. For more information on that I refer to my detailed description of the programmable decade resistor. (I actually didn’t realize that until I had a look at the schematics for the first time while writing this post…)

Also worth mentioning is the fact that the two funny looking “holes” in the top-left and top-right corners of the unit are “4/13 coaxial connectors”. To be honest, I never heard of those before. Apparently one could buy different adapters, including some inserts for a BNC connection. Since I have two of those “4/13 coaxial” cables I could build my own adapters if I ever felt the need to use the decade resistor for AC signals.

Now, let’s see whether this decade is in spec three decades later (pun intended). For this test I use an Agilent 34401A’s 6.5 digit multimeter. Its cal string states “16 AUG 2006 23.6°C”. More than 15 years later and at 18.8°C I measured my 1k precision resistor at 1.000,008,4k (+8.4ppm). This should suffice. (Note that there are quite large tolerances even for the 24h spec of the 34401A. This is just a hobbyist measuring an old decade box with a not quite as old 6.5 digit multimeter with effectively unknown cal history.)

All measurements are done at full resolution and with NPLC=100, triggered and recorded via SCPI. Setting the B2086’s resistance value, triggering and performing the measurement for 56 test points took me just under 10 minutes. Here are the results:

Applied value
(\(\Omega\))
Indicated value
(\(\Omega\))
Deviation
(\(\Omega\))
Deviation
(\(\%\))
Min
(\(\Omega\))
Max
(\(\Omega\))
Result
0.20.139575-0.060-30.21250.1050.295PASS
11.1536390.15415.36390.8991.101FAIL
22.1624860.1628.12431.8782.122FAIL
33.1735850.1745.78622.8573.143FAIL
44.1838060.1844.59513.8364.164FAIL
55.1920200.1923.84044.8155.185FAIL
66.2039340.2043.39895.7946.206PASS
77.2188920.2193.12706.7737.227PASS
88.2261790.2262.82727.7528.248PASS
99.2412270.2412.68038.7319.269PASS
1010.168070.1681.68079.87910.121FAIL
2020.162680.1630.813419.83820.162FAIL
3030.183450.1830.611529.79730.203PASS
4040.184350.1840.460939.75640.244PASS
5050.198900.1990.397849.71550.285PASS
6060.206690.2070.344559.67460.326PASS
7070.225270.2250.321869.63370.367PASS
8080.232300.2320.290479.59280.408PASS
9090.251310.2510.279289.55190.449PASS
100100.26260.2630.262699.764100.236FAIL
200200.31770.3180.1589199.608200.392PASS
300300.37160.3720.1239299.452300.548PASS
400400.44890.4490.1122399.296400.704PASS
500500.52190.5220.1044499.140500.860PASS
600600.47150.4720.0786598.984601.016PASS
700700.53570.5360.0765698.828701.172PASS
800800.59670.5970.0746798.672801.328PASS
900900.66390.6640.0738898.516901.484PASS
1000999.8580-0.142-0.0142998.4141001.586PASS
20002000.9590.9590.04791996.9082003.092PASS
30003000.6280.6280.02092995.4023004.598PASS
40004001.0531.0530.02633993.8964006.104PASS
50005000.7310.7310.01464992.3905007.610PASS
60006001.2321.2320.02055990.8846009.116PASS
70007000.9070.9070.01306989.3787010.622PASS
80008002.5042.5040.03137987.8728012.128PASS
90009002.1742.1740.02428986.3669013.634PASS
100009996.537-3.463-0.03469984.91410015.09PASS
2000019998.83-1.167-0.005819969.9120030.09PASS
3000029995.17-4.832-0.016129954.9030045.10PASS
4000039999.83-0.172-0.000439939.9040060.10PASS
5000049996.16-3.839-0.007749924.8950075.11PASS
6000059996.78-3.224-0.005459909.8860090.12PASS
7000069993.01-6.990-0.010069894.8870105.12PASS
8000079996.67-3.327-0.004279879.8780120.13PASS
9000089992.74-7.265-0.008189864.8790135.13PASS
10000099946.29-53.71-0.053799849.91100150.1PASS
200000200231.2231.20.1156199699.9200300.1PASS
300000300173.0173.00.0577299549.9300450.1PASS
400000400431.3431.30.1078399399.9400600.1PASS
500000500369.5369.50.0739499249.9500750.1PASS
600000600551.1551.10.0919599099.9600900.1PASS
700000700486.8486.80.0695698949.9701050.1PASS
800000800524.2524.20.0655798799.9801200.1PASS
900000900456.7456.70.0507898649.9901350.1PASS
9999991000435435.80.0436998498.61001499PASS
Calibration result for 56 test points

Especially for the values above and not including \(100\Omega\) the decade resistor does a really nice job. The switches might contribute to the deviation in the lower ranges despite their “dust-free design” and “self-cleaning” properties. But they still feel very solid and the readings were stable, so for me that’s fine.


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