Hello Mr. Pettis,
thanks for your elaborate analysis, which I mostly agree, apart from two aspects:
If the observer wants to measure the effect of a change in temperature between two points, how fast or slow the external temperature changes is irrelevant, only that the resistor is given enough time to stabilize at the second temperature internally is important. The same thing applies when returning the resistor to the initial conditions. Additionally, the greater the stimulus change, the greater the hysteresis, this is not to say that the hysteresis will be a large value but hysteresis tends to be larger with larger stimulus change.
That's a kind of contradiction in itself.. as that's the crucial point , if the measurement is done in quasi equilibrium, or not..
The hysteresis measurement very well depends on the speed of the temperature change!
Andreas measurements with different temperature change rates illustrate that.
The physical effect, which causes hysteresis, mostly can be described like something like a friction force.
If this force as is "weak", you will get fast recovery or fast creep effects.
If this force is strong, you will get a very stiff hysteresis, and maybe no practical observable creeping (glass state).
Equivalently this may also be described with a relaxation time constant for these hysteresis effects, (strong force <=> long relaxation time constant and vice versa)
I observed something like 1ppm/30min in one of the measurements on Andreas resistors.
Therefore, if the temperature change is much slower compared to this time constant, the sample can relax to the equilibrium state at the different temperature points, and you may get a very narrow hysteresis loop, compared to the case, when the change is much faster than the time constant.
For the measurement of T.C. curves, that may also give totally different results, if you determine T.C. linearily or by box method.
Dr. Frank, as I recall, the econistors specify 0±3PPM/°C TCR 0°C to +85°C, your batch is out of specification, the 0±5PPM/°C TCR applies above +85°C or below 0°C. Given that they claim a lengthy thermal conditioning cycle (7 days), something or someone got sloppy on production.
Well, the econistors are not very well specified (similar to Vishay)
That 3ppm/K is a TYPICAL value only, therefore most of the resistors are definitely within spec.
The MAXIMUM 5ppm/K over -55.. + 125°C strongly indicate that the 14 and 7.7ppm/K are outside, but here again, I have the same specification struggle as with Vishay, that is the averaging calculation by a box or a butterfly definition..
For metrological purposes (18..35°C), I need instead the physical definition, i.e. T.C. = dR/dT, or exactly the R(T) curves we are measuring here.
The box and butterfly definition mostly determine the T.C. by measuring at 3 or 5 temperatures only, and then average the resistance change by the temperature range.
This may give much lower T.C. values, if the R(T) curve is not linear over temperature, but has minima and maxima.
Frank