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Hello,
I have found the root cause for the "jumps" at low temperatures.
Found it accidently when trying to add some thermal isolation.
The package is _very_ sensitive to any touching. (package stress).
Jumps of several 10-100uV can be observed.
The fault that I have made is to put the LS8-package directly on the PCB to ease soldering the wire from the other side to the GND Pin.
So the package was touching the PCB (and in between there was the plastic sticker with the number from previous T.C. measurement 10 years ago).
I solved this by rewiring and placing some spacer between PCB and the reference.
After soldering the spacer was removed.
Now I got a "soldering shift" in output voltage and a new fast initial ageing.
So it will take some time until the reference will be more stable.
But I fear there will be still a 3-4 ppm hysteresis.
Another observation was that there might be some temperature sensor drift.
I am using the chip internal temperature dependant trim voltage for the temperature sensing.
And it looks that either the absolute voltage drifts with reference voltage or there is a problem
That I have different reference voltages from LT1236+bridge evaluation
and the 12 Bit ADC (where VRef = VDD from a 5V regulator).
with best regards
Andreas
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Hello,
and the same for ADC#34.
Initial drift is a bit lower because I had more time between soldering and first measurement.
2nd picture: the blue line is from previous T.C. measurement showing the drift by re-mounting.
Against red: the current T.C. measurement. Hysteresis here ~4 ppm. And 1 ppm drift between cycles.
3rd picture: the drift between the temperature measurements red: new green before re-mounting.
But of course there could be also that the sensor8 distance which I use as master temperature
to the LT1236 reference is slightly different due to re-moung.
With best regards
Andreas
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Mechanical and thermal stresses play havoc with all references. My plan, as yet unrealized, is to space the device upside down and dead-bug the wiring with fine constantan or manganin. The device is small so the wires should support it just fine. Using ABC (anything but copper) will reduce the thermal flow out of the part and probably increase the stability and lower the power requirements. I'm guessing the added resistance of the wiring will be a constant and not affect anything, but that remains to be seen, depending on the current flow for heating.
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Hello,
Manganin would be good.
Constantan has too much thermal voltage against copper.
And the chips usually have 2-3 deg C more temperature than the environment.
(even when the ground pin is soldered to the PCB).
with best regards
Andreas
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Another problem with konstantan wire is that it is hard to solder. Maganin wire is easy to solder.