Having a ruler would make it too easy, (just measure 60mm of wire)
judging by the way the question is phrased I assume that you have to use
just the equipment supplied. Wire, DVM, power supply and 10R resistor,

So,
1. hook up the 10R resistor in series with the resistance wire and
apply power from the laboratory supply.

2. Put the DVM in it voltage mode, to measure 1V as accurately as possible.
(since it is 0.1 in 200, we can assume it is 0 to 1999 in voltage mode)
Connect the DVM across the 10R resistor, so we now calculate the current
flowing through the wire, for ease of calculation we can choose a current
value that makes the maths easier. Say 10 volts, this means we have 1A
flowing through the wire. (This is as much as we want with a 10W
resistor anyway)

Now move the DVM to measure from the junction between the wire and the
resistor, and slide the other meter probe up the wire to measure 30mv
0.030 = 1 * 0.030.

Now we have a problem, the accuracy required is 5%, if the 10R resistor
is only 10% and/or the multimeter doesn't have a good millivolt range we
are in trouble with guaranteeing the 5% accuracy.  So reel off enough wire
to make the voltage 8*0.03= 240mv and fold in half 3 times.  (side benefit
is that will increase the current handling capacity of the shunt.)

I would crimp the wire ends into a ferrule, so a correction needs to be
made to allow for the length inside the crimp.


I was once told by a client, that when looking for employees for embedded
development work, he looked for candidates that had a "twitch" and a little
bit off the wall. His reasoning that you needed REALLY crazy people for this
kind of work.


>What is precision of that DVM in voltmeter mode ? ;)
>Do you have sharp cutters and precise ruler as well? ;)
>
>WBR Dmitry.
>
>PS.
>
>(Also I think it's better to cover shunt ends with solder
>so that length is extra)
>
>
>
>
>"Peter L. Peres" wrote:
>>
>> Why not set up a small exam that involves tasks the interviewee would be
>> asked to perform in his/her job and deliver it orally instead of wasting
>> time to find out what the person does in its free time ? You would choose
>> tasks that would not require previous knowledge of the specific equipment
>> you are really using. Like 'how would you make and test a 5% 30 miliohm
>> shunt given 0.5 ohm/meter resistance wire, a common DVM that is only
>> accurate to the nearest 0.1 ohm on the 200 ohm scale, a 10R 10W resistor
>> and a laboratory power supply'.
>>
>

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