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Mettler TM15 RDT PT100 mecanical temperature display 1970 test teardown

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TimFox:
The technique is similar to analog chart recorders, where the pen position is encoded by a potentiometer, whose voltage output is compared to the analog input.
I remember old 40-turn "servo" helical potentiometers that had linearity on the order of 0.01%.

MK14:

--- Quote from: TimFox on November 02, 2023, 01:52:23 pm ---The technique is similar to analog chart recorders, where the pen position is encoded by a potentiometer, whose voltage output is compared to the analog input.
I remember old 40-turn "servo" helical potentiometers that had linearity on the order of 0.01%.

--- End quote ---

Wow!

I'm surprised the potentiometers, don't keep wearing out, in such applications.

I suppose such instruments were used a lot, before digital logic became common place.

oz2cpu:
exactly, those potentiometers is mostlikely what define the cost of this unit !

BOURNS the largest blue model

MK14:
The following free PDF handbook, seems to nicely fill in the details.  For anyone who wants to know more about precision (and other) potentiometers, like I did.

https://www.bourns.com/docs/technical-documents/technical-library/corporate/OnlinePotentiometerHandbook.pdf

They seem to have helped fill in the gap, for creating powerful (e.g. control and measurement) functionality, until cheaper electronics (especially integrated circuits), could fill in the void, in later years.

Edit: Also for trimmers:   https://www.bourns.com/docs/technical-documents/technical-library/trimmers/technical-articles/trmrpmr.pdf

Vgkid:
Thanks for the teardown, I have never seen a thermometer with a mechanical digital displsy.

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