I measured R(T) / T.C. for 5 different precision resistor technologies, all with the same setup, i.e. using the 3458A with 4W and Offset Compensation, a precision NTC, in the same thermal box, with an aluminium DUT holder, and with equal temperature profile.
The leftmost, black ones are 2 bulk metal foil resistors from Andreas, Z201 #2, Z-foil, TC < 1ppm/K and S102JT #1, C-foil, TC ~ 2ppm/K both have 1.0000k, 0.01%, Vishay brand.
The 3rd, green resistor is also a Z201, 49k99, 0.01%, but in an older packaging from about 2004.
The 4th, blue resistor is a bulk metal foil from Alpha Electronics, type FLCY, TC typ. 2.5ppm/K, 25k, 0.1%
The 5th is an econistor from G.R., 1k, 0.1%, TC < 5ppm/K
The 1k resistors were measured at 1mA, the 25k and 49k99 at 100µA
Stability over time of the 3458A was monitored by an external 10.00000k reference resistor, and its deviation after the hours of experiment was < 0.5ppm in all cases.
The thermal box was inserted in a small beer cooling box, so that a stable air column was formed inside, which gives a continuous temperature layering, from cold at the bottom to room temperature at the top of the box. (picture shows measurement on another box)
By this 3 fold thermal encapsulation, and the thermal inertia of aluminium block and box, NTC sensor and DUT were on the same temperature during the slow temperature changes.
Inserting a cooling pad quickly cooled the assembly down to 10°C, and an incandescent lamp, by its IR emission, quickly heated to about 40°C.
The results show a pronounced hysteresis figure of both black BMF resistors, especially as the end values do not match the starting values.
Also, a virgin curve can be observed.
After the thermal cycle, both resistors were held at a constant temperature of about 26°C.
A creeping of the (hysteretic) resistance value, directing towards the initial value, could be observed, in both cases about 1ppm/30min.
The Z201 shows a very bulged / distorted hysteresis loop, probably due to the creeping behaviour.
At this point, I have to apologize Andreas, for casting doubts on his measurements!
His measurements setup, using a much lesser costly equipment, gave qualitatively same or very similar results, and they were nearly on the same order of noise figures.
Well done, Andreas!
Compare here:
https://www.eevblog.com/forum/projects/t-c-measurements-on-precision-resistors/msg462299/#msg462299and here:
https://www.eevblog.com/forum/projects/t-c-measurements-on-precision-resistors/msg462303/#msg462303The three latter resistors do not show hysteresis, identifiable by the fact that the initial resistance value at ~ 26°C always closely matches the value after the temperature cycle.
Therefore, only a slight temperature lag between sensor and DUT can be observed, due to fast cooling/heating.
For the black BMFs, I can hardly assign a T.C., due to the hysteresis.
The Z201 changes about 5ppm in a window of 30°C, that's about 0.2ppm/K average TC.
The S102J is practically useless as a stable resistor, as the big hysteresis spoils the 2ppm/K specification.
The old Z201, 49k99, has a linear TC of +0.5ppm/K, w/o hysteresis.. very good.
The AE FLCY, 25k has a slightly hyperbolic characteristic; the linear TC would be around -0.9ppm/K.
The econistor has a relatively high, linear TC of about 4.6ppm/K.
I've already seen a better sample, of about +2ppm/K, recently.
Anyhow, I will have to measure all the econistors, 5EA of 1k and 12k, for my LTZ1000 , to match these pairs for best overall TC of the reference circuitry
There's one question left, for discussion:
I really wonder, why these newer, black BMF from Vishay have this hysteresis and creeping effects, in comparison to the oder Z201, and also the VHP202Z (in AT51 XTAL type can) I also have measured.
Maybe, that the smaller mold case causes this effect, or they may have simplified the inner construction, maybe omitting a mechanical buffer layer over the resistance element.