[Test-Equipment] Leeds and Northrup KS-10376 Null Voltage Test Set

[John Kolb]

I don't know anything specific about a Null Voltage Test Set, but 
sounds like it's a distant cousin
of differential voltmeters which I spend several years on as an 
engineering tech at Wavetek.

You can determine the galvanometer sensitivity by using your 10V 
reference supply and shorting the measured voltage
terminals to ground, in which case you should get a null with the 
dials all zero.  Then adjust the dials
for full scale reading on the galvanometer.  The dial reading will 
indicate what small part of 10V full scale is.

I would not exceed the 250 volt rating - you risk overheating the 
resistors and destroying the accuracy.

Are there actual adjustments to calibrate, or does "calibration" 
consist of testing to see if it still meets spec?

You can get an indication of basic accuracy by measuring each 
resistor in the first one or two sections of the
KVD with a really high resolution ohmmeter.  Another approach would 
be to get a handful of wire wound resistors
of the same value, and put in series with a 10 ohm pot and adjust all 
to be identical values.  Place some number
in series and make resistor ratio measurements.  With three in 
series, the dials should read .333333 and .666667
at the two taps.  4 resistors should read .25000, .50000, and .75000, etc.

John

At 05:56 PM 5/23/2011, you wrote:
>Does anyone have any information on a Leeds and Northrup KS-10376 
>Null Voltage Test Set, made for Western Electric Co.? It appears to 
>be a 4 decade Kelvin-Varley divider plus one decade wirewound pot, 
>plus a galvanometer for the null indication, along with some 
>switching that enables the following measurements:
>
>1. potentiometric voltage ratio measurement, with an external +/-250 
>volt reference supply
>2. resistor ratio measurement, with an external 45 volt dry cell battery
>3. resistance measurement, with an external 45 volt dry cell battery
>
>The decade string is 100K ohms.
>
>I don't have a manual; it's got a schematic varnished onto the 
>inside of the case, and some basic operating instructions varnished 
>onto the inside of the lid.
>
>I hope to use this, along with homebrew stable HV and LV power 
>supplies and an AD597 voltage reference such as the one from Geller 
>Labs, to calibrate the DC ranges on my VTVM collection (HP-410B, 
>HP-412A, HP-410C, Heath IM-11, a sick HP 3456A, and more to come I'm 
>sure). I'm wondering about:
>
>* what's it's specified accuracy? It's got a resolution of 10 ppm; 
>was it anywhere near that accurate? (My unit was last calibrated in 
>1958 at Bonica Arsenal, so I have no idea what its accuracy is now. 
>I probably can't afford to have a calibration lab look at it. I do 
>have a couple of inexpensive Vishay 0.1% resistors, so I can at 
>least get some idea of whether it's completely out of whack or not.)
>
>* what's the maximum current the divider can take? I'd like to be 
>able to compare 1KV against a 10V reference standard; with 100K 
>resistance, the individual decade resistors will have to take 10 ma 
>* 100 V or 1 Watt. The instructions in the lid imply a limit of 
>250V, or 1/4 Watt per resistor.
>
>* what's the sensitivity of the galvanometer? I'd like to be able to 
>feed the divider from the 10V reference and set my low-voltage 
>supply to 1V or less. I suspect the galvanometer isn't sensitive 
>enough for these low voltages; I'm contemplating adding a couple of 
>banana jacks so I can use my HP 425A DC micro volt-ammeter as a more 
>sensitive null detector.
>
>Eventually I hope to tinker up an AC calibrator, too.
>
>Or should I just look for a used HP 738AR or 738BR?
>
>Best regards,
>-Steve
>
>--
>Steve Byan <stevebyan at me.com>
>Littleton, MA 01460
>
>
>
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