Re: Ambient temperature control

This study suggests that for disc drives there is no advantage in cooling them below around 40 or 50 deg C.

John

John

There can be for some high performance low level OPamps. Deliberately running them as cold as is allowed helps take the LF noise floor down and by more than you would predict from Johnson noise. ISTR there was a patent for doing this back in the 1980's. Prior to that they tended to heat the front end to obtain temperature stability and low drift.

Depends how temperature sensitive the thing is that you are protecting. The example I recall they were aiming for medium term stable 6 sig fig measurements with the lowest possible noise.

If all you're thinking of is MTBF, adding the complexity of an active cooling element is a big step in the wrong direction for the system.

Reducing the thermal impedance of the source, to ambient is the usual way to go, when addressing a specific aging factor.

RL

Tubes? The cathodes fail eventually. Reduce filament voltage and suffer the reduced gain. Better yet, don't use tubes.

But for most parts that dissipate power, the big win is to have some air flow. A fan can reduce the theta of your parts by 2:1.

Nowadays, parts are very good, with failure rates in the ballpark of one failure per billion hours, the Bellcore and MIL217 FITS numbers.

BITD you tended to get popcorn noise from ions migrating around the surface and in deposited (rather than thermal) oxide. Cooling helped that a lot. Nowadays processes are generally clean enough that you don't get a lot of mobile ions.

You don't want to use a thermostat with TECs anyway--they die very rapidly, especially the soft-solder ones (Laird/Melcor).

Cheers

Phil Hobbs

Anybody who tries to use bang-bang control with a TEC will run into that. TEC's are non-linear devices, and work best when the current through them doesn't vary much.

Sloman A.W., Buggs P., Molloy J., and Stewart D. “A microcontroller-based driver to stabilise the temperature of an optical stage to 1mK in the range 4C to 38C, using a Peltier heat pump and a thermistor sensor” Measurement Science and Technology, 7 1653-64 (1996)

used a TEC, and the product didn't die in the field, or not a least over the roughly ten years it was on the market. My boss had had a run in with bang-bang control of TECs in another (earlier) product, and that hadn't gone well, so we were well aware of the problem (and the paper does go into it, briefly).

This was an example of a demonstrated and documented failure mode in a specific component (glass electrolysis) that is/was largely ignored by the general user.

If you know what the specific aging mechanism is that you're trying to address, your methods of improving mtbf will be more effective.

RL

What's the mtbf of a fan? a compressor? a pump? . . . . or a clamp and a block of aluminum?

Ambient and component temperatures are freely obtained and carefully controlled elements in mtbf documentation recording methods.

The former requires $$ equipment.

RL

What are the HVAC costs in data processing and server facilities?

That's just to maintain ambient <40C.

RL

Given non-junk products from you-know-where, most electronics failures are not from classic parts failure. Few real products, in the field, get close to the standard-calculated-method MTBF rates. They die from bad design, bad packaging and soldering, or external effects like ESD.

Sometimes one of our customers will ask for a calculated MTBF, so we dutifully crank one out. We both know that the number is prfetty much fantasy.

A standard calculation can be rubbish - often it will to be deliberately fudged to get an acceptable result - ignoring actual temp, stress or mtbf measurements in favor of guestimates or assumptions.

'You can't handle the truth !'

An external esd event is predictable and the strike count can be addressed for a specified environment, by built-in design, by opperator precaution or by environmental proscription.

RL

You know what a brass tack is?

RL

This is just a space maker.

RL