Hi,
searching for "The Ampere" at home I took some aluminium and a milling machine and made a simple housing for shunt resisitors (image_1 and image_2). I filled these casings with an Isabellenhütte PBH 1R0 1% and an Isabellenhütte Isaplan A-H2 0R1 0,1% (Manganin). And then I had to try to characterize them... Perhaps starting with the temperature coefficient? Not that easy if using a 6,5 digit multimeter. Keithley praises the current-reversal (delta-technique) for this purpose but I could find some application notes using this method only, no real-world measurement data. But I found a button "V1-V2" on my Keithley 2182... We will see what will happen...
Therefore I started playing around connecting the multimeters with GPIB-cables and a Prologix-adapter and some "programming" using EZGPIB and doing some preliminary tests... After adding some additional cables and sensors and meters and some high-performance thermal insulation to the experiment it ended like shown in image_3...
This can be understood much easier looking at mage_4... or image_5...
The voltage at the shunt resistor was measured using the K2182. The K2182 was configured to 5NPLC, fixed range 10 mV, LSYNC off, heavy filtering: 100 values into the digital filter, delta measurement, 100 ms delay. The data were collected via GPIB. As I do not own a programmble current source I made such one using my K 230 voltage source and my 1 k "reference resistor" (which has a Dale RH 50 inside, measured t.c. = -0,75 ppm/K). The 230 was programmed to deliver +/- 10,00 V and was triggered by the VMCout of the 2182 (as necessary for delta-measurent). The moderate stability of the source might be the weakest point of this setup.
The temperature control was done using a very simple home-made hot plate (2 pcs. 10R power resistors (50 watt) mounted beneath the aluminium plate). As the casing of the shunt is milled flat there is a good thermal contact between the hot plate and the DUT. The temperature at the heater was measured with a TEK DMM4050 using a Pt100. These data were fed into the programm and were used for the graphs and for temperature regulation: if necessary the program initiated 0.5 s heating pulses by commanding a Agilent 66332A power supply (connected vis RS232) which feeds the heater.
An additional Pt100 was placed inside the boring of the shunt to monitor the temperature of the shunt using a Rohde&Schwarz UDL45 multimeter. This temperature was observed "off-line" as I needed the serial port for the 66332A. In steady state the offset T(shunt) - T(heater) was constant at 0,1 °C.
And the room temperature was monitored offline ( as I run out of GPIB-cables) using a HP 3456A with a thermistor. The room temperature was held within (indicated) 22,7 °C +/- 0.2 °C by opening or closing the door...
And these are the results:
The first result (image 6): comparing the non-equilbrated setup without (first part) an with current reversal (second part). The setup was undisturbed, only the delta mode was switched on after 600 s by the program... OK, better to use the delta mode for further experiments.
Then I examinded the Isabellenhütte PBH 1R0 (image 7a and 7b, two separate runs). These runs differed a little in the heating parameters. And from these data I decided to use the t.c. of 10 ppm/K in future.
Seems to be easy. Then try a 0R1... The results are more noisy but I think that's acceptable in the nV region (image_8a and image_8b). From the data shown in image_8a I assume a dR/R = 32 ppm and a dT = 5 K leading to approx. t.c. = 6,5 ppm/K.
The changes in resistance could be seen more clearly when performing larger temperature steps (8b). This graph gives something like t.c. = 5,5 ppm/K. Unfortunately EZGPIB crashed during the second experiment (8b at 5600 s). Therefore I had to restart the experiment quickly and I glued the parts together manually for graphing. No other corrections were made.
My summary:
- it's a lot of fun to try such an semi-automated experiment - much better than watching tv,
- it seems to be a nice real-life test for the performance of the instruments,
- it's not that complicated to control measurement instruments by EZGPIB and serial or GPIB-Ports, EZGPIB ist really easy and good for control via RS232 also,
- the "program" might be useful for other experiments and can be modified easily,
- current reversal technique will be advisable for such type of measurements,
- it seems to be possible to do measurements in the 1 to 10 nV-region at home,
- the measurements will give better results with a larger current, certainly. But I don't have a powerful programmable bipolar current souce or a good 100R resistor.
- I have to add another meter to collect more data... e. g. the temperature of the DUT.
- with some luck and filtering and close control of environmental conditions it seems to be possible to achieve a stability of around 2 to 5 ppm/h with a K230,
- the t.c. of my current shunts can be assumed as 7 ppm/K (max.) for 0R1 and 10 ppm/K (max.) for 1R0 around room temperature. Not bad compared to the specifications of approx. 30 ppm/K (although the specs cover a larger temperature range),
- this current-reversal technique might be usable for the transfer from 100R to 10R to 1R to 0.1R also? I have to make a 100R and a 10R to test this...
- I have to gain some further experience before I will call this "a real measurement"...
Best regards
Marcus
P.S. In the meantime a third run of the 0R1 was completed without crash (image_9):
to 1300 s forced cooling by fan,
1300 s - wrapping the resistor with the towel
2000 s - heating to 23 °C. Temperature difference to ambient too small, heat loss too small, bad regulation
3700 s- heating to 25 °C. dR = 14 ppm
5650 s- heating to 27 °C. dR = 11 ppm
7600 s- heating to 29 °C. dR = 6 ppm
If over-interpreting these data (decrease in change of resistance with temperature) it might be possible to assume the parabola-like shape of the R(T)-curve as indicated in the datasheet.