But I will not handle with cyrogenic liquids.
On the other side the thermal block will increase the effort for measuring different sizes of resistors.
I already asked myself how you did your 0.3 ppm/K measurement.
I hope you will deliver some details soon:
- temperature range
- temperature gradient
It could be possible that the bond of the metal foil to the ceramic substrate has a time constant regarding hysteresis.
So I think the ramp speed could also have a effect on hysteresis amount even if the temperature sensor is mounted correct.
I have seen such a effect on the LT1236AILS8-5 reference. But on the other side it could be also the temperature sensor mounting.
with best regards
Andreas
Hello Andreas,
the story about liquid Helium or Nitrogen was an example only.
At the physics institute, I used to measure that way, and also calibrated our thermometers in the temperature range of 2K ... 300K.
For this purpose here, simply use a cooling pad, or even your heater instead.
And I really meant that using an aluminium block is a simple thing..
Aluminium bars, 1m long and 16x16 or 25x25 are available in your next DIY store (
Baumarkt).
Saw off a piece of appropriate length, and drill several holes completely through that block, so that you may attach different resistors in that block.
For tubular resistors and the NTC it's very easy, add 1/10..2/10 mm for the diameter.
For rectangular resistors, you have to drill and file a slot, well right, that's a little bit more effort.
Build one additional block for your reference resistor.
I use an HP3458A in 4W Ohm mode, with offset compensation and 0.1ppm resolution.
Consecutive readings on the same resistor are also stable to <= +/- 0.2ppm, at 100 NPLC (4sec measuring time).
Measuring my 5 VHP202Z one after each other several times within 10..20 minutes, I always get repeatable readings which differ not more than 0.2ppm for the same resistor.
The ambient and internal temperature is stable to <= 0.1°C in that time period.
Therefore, the transfer stability is about 0.2ppm.
Even for much longer times, keeping the temperature stable, gives stabilities in that order of magnitude.
The T.C. measurement on the V334 took about 8 hours, see diagrams.
The vertical graticule is 0.2ppm wide.
Each measurement point is simply read once from the instrument, without further averaging than the NPLC 100 measuring time. I also apply a calibration factor for the HP3458A (derived from the group of these 5 VHP202Z), but that's secondary for the T.C.
There is a jitter from point to point about 0.2ppm wide.
Those Ohm measurements are relatively sensitive, and the DUT was connected with four 1m long, unshielded cables only.
I simply let the linear regression function average out all this jitter for determination of the T.C.
In the beginning, heating was done too quickly, so the curve deviates from the average line by a bigger amount. Therefore, about the first 100 points were skipped for the T.C. calculation.
For the rest of the temperature cycle, over 6h, the measurements follow nicely the linear regression line, without a noteworthy hysteresis.
If you compare the starting measurements around 25°C (#185) to those at the same temperature after 6h (#378), they agree within +/- 0.2ppm.
That's quite stable, I think.
The internal temperature changed not more than +/-0.2°C.
There are several glitches visible in the measurement, caused by myself, when I moved the heat reservoirs inside and outside of the cooler box.
This resistor itself obviously shows no hysteresis.
If you would repeat that measurement with a much faster temperature gradient, you might see a hysteresis loop, which would be caused by the temperature lag between DUT and T-sensor only.
By the shape of the hysteresis loop, you could judge, how good your temperature coupling is.
Frank