[EE] Zero ohm resistors

[Sean Breheny]

I thought this was a joke when I first saw it but some investigation leads
me to believe that it is real:

http://www.ohm-labs.com/resistance-standards/100-0-standard.html

It seems that this device (a four-terminal device where the voltage between
the sense terminals is zero regardless of the amount of current flow
between the other pair) was originally developed to allow series and
parallel combinations of very accurate four-terminal resistors, producing
an overall four terminal resistor with the ideal series or parallel
combination resistance of the four-terminal resistors that comprise it.

What I don't understand, though, is its utility as a stand-alone item. You
could "do what it says on the tin" by just completely isolating the sense
terminals from the force terminals and shorting the sense terminals
together and the force terminals together. The only difference I can see is
that there would not be conductivity between the force terminals and sense
terminals and so therefore there could be a voltage difference between the
two pairs. But then again it would seem to me that you could achieve the
same effect with simply a block of copper where the force terminals were
placed anywhere on the block but close to each other, while the sense
terminals were placed far away, on the same block, from the force
terminals, but also close to each other.

Inside this "zero ohm standard resistor" is indeed a thick copper disk
(from what I've read) where the terminals are located in a very symmetrical
configuration so that the voltage drop due to the force terminals has
exactly the same value at the two places where the sense terminals connect.

Sean

[RussellMc]

Sean: Black hole
Others: Maybe.

Crude desscription of Hamon 10:1 reference divider.

Take 10 x equal R's Res = R at "good precision" - say R0-R9

Make 3 x serial groups R123 R456 R789
Parallel 3 x 3Rs = R3p - Res = R
Place R3p in series with R0.
This forms a 2:1 divider.

Place all R's 1-9n in series= R19 Res = 9R
Use R19 + R0 as a divider Vin to R19 to R0 to ground
V_R0 = 0.1 x Vin.

ie if all R's are equal you have a 10:1 divider and this can be checked for
calibration with the 1:1 setup.

Used to calibrate meters and most anything else.

See:
B. V. Hamon, “A 1-100 W build-up resistor for the calibration of
standard resistors, J. Sci. Instr., vol 31, pp 450-453, Dec. 1954.

______________________________________



NIST Technical Note 1458 NIST Measurement Service for DC Standard Resistors
2003

https://www.nist.gov/sites/default/files/documents/calibrations/tn1458.pdf

B. V. Hamon, “A 1-100 W build-up resistor for the calibration of
standard resistors, J. Sci. Instr., vol 31, pp 450-453, Dec. 1954.

D. G. Jarrett, “Evaluation of guarded high-resistance Hamon
transfer standards,” IEEE Trans. Instrum. Meas., vol. 46, pp. 324-328, Apr.
1999


NIST Technical Note 1298 NIST Measurement Service for DC Standard Resistors
1992

http://ws680.nist.gov/publication/get_pdf.cfm?pub_id=17477


Your device - different page

https://www.ltm.as/ohmlabs-100-0/ohmlabs-100-0-zero-ohm-standard


Interesting, but mainly for the *'nice' picture
<https://www.eevblog.com/forum/chat/what-did-you-buy-today-post-your-latest-purchase!/?action=dlattach;attach=234156;image>*
posted by Gamalot


https://www.eevblog.com/forum/metrology/low-ohm-precision-resistor-standard-and-testing/

Hamon trasnfer standards - many mentions

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4865284/


And more - this time at VERY high resistance values

https://xdevs.com/doc/_Metrology/10353.pdf


_________________________________

DIY Hamon reference dividers.
10:1 and 100:1
Informal comparisons with Fluke 752A are made.

Interesting reading (YMMV :-) )


https://www.eevblog.com/forum/testgear/anyone-else-built-a-hamon-divider/

Many links

Fluke 752A schematic (boring :-) )

https://xdevs.com/doc/Fluke/752A/Fluke_752A_Schematic.pdf



Russell

[a***@stfc.ac.uk]

What I don't understand, though, is its utility as a stand-alone item. You could "do what it says on
the tin" by just completely isolating the sense terminals from the force terminals and shorting the
sense terminals together and the force terminals together. The only difference I can see is that
there would not be conductivity between the force terminals and sense terminals and so therefore
there could be a voltage difference between the two pairs.

I can see the utility of a device like this in calibrating temperature bridges that use four terminal measurements on low resistance PRT devices that are used for measuring very low temperatures. We currently use Rhodium Iron PRTs which have a room temperature resistance of around 36 ohms, and are taking them down to liquid nitrogen temperatures. The measuring bridge has a requirement that the cable between the bridge and the sensor has no more than 10 ohms per wire, which starts adding up when using 30AWG wire to limit the heat conduction down to the sensor from the outside world.

So yes, I can see it being a useful device in the calibration of very low temperature measurement.