Products > Test Equipment
DMM fans - noisy friends?
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alm:

--- Quote from: guenthert on March 28, 2022, 10:54:00 pm ---First generation of HP3456A had them, later revisions not (I'm not aware of other major changes between the revisions).

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They moved a TO-3 power transistor from inside the case to the back. Presumably moving some of the heat dissipation outside the case.


--- Quote from: guenthert on March 28, 2022, 10:54:00 pm ---Top end HP3458A has one,  yet the top end models of Datron, Fluke achieve comparable precision (not speed though) without.  And even the 8.5 digit Datron 1271, markedly intended for industrial ATE, doesn't have one.

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I believe the high-speed comparators necessary to give the 3458A it's high-speed digitizer feature get quite hot. This may well have played a role in the use of a fan. I don't believe the Datron/Fluke designs have this same high speed.


--- Quote from: guenthert on March 29, 2022, 06:24:35 pm ---Well, yes, for voltage dividers temperature gradient is relevant rather than the temperature per se, but that's not the case for other components, e.g. shunt resistors.

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Temperature gradients are also responsible for thermal EMFs.
mapleLC:
I've had success so far with the following and Noctua fans:

Keithley 619 - also switched fan from AC to DC
Keithley 237 - also switched fan from AC to DC

Agilent 546xx oscilloscope (x 2)

Several network switches

Its situational.  I don't plan to run any of these at industrial levels, so they don't get hot.
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