[time-nuts] HP5065A environmental sensitivities

[Magnus Danielson]

Hi Bob,

On 05/22/2016 05:21 PM, Bob Camp wrote:
> Hi
>
>> On May 22, 2016, at 10:49 AM, Attila Kinali <attila at kinali.ch> wrote:
>>
>> Hoi Poul-Henning,
>>
>> On Fri, 20 May 2016 09:52:39 +0000
>> "Poul-Henning Kamp" <phk at phk.freebsd.dk> wrote:
>>
>>>> Temperature effects are by far the largest effects we have to deal with.
>>>
>>> Which is why you'd be much better of with 20 sensors at 16 bits,
>>> than a single sensor at 24 bits.
>>
>> Does the HP5065 have such huge temperature gradients/differentials inside?
>
> At least 5C offset relative to an external sensor. Likely more in some rack installations. Past
> that it depends on how close the item of interest is to the oven assembly.

To explain a little more.

The 5065A/B has a design that relies on self-convection. Depending on 
which generation, the AC rectifier is sitting on the PCB or on the 
chassi for cooling. Similarly the switcher on the A15 board can run a 
bit hot. This alone makes me recommend that the 5065 is put such that 
there is self-convection. I run mine free-standing.

Making the 5065 more temperature stable is definitely recommended, but 
that is to some degree orthogonal from handling the heat produced.
PHKs replacement of PSU details helps to reduce the heat and also 
produces more stable power-supply, which is a good step in the right 
direction on both accounts.

With a little cleanup of the PSU, thermal management have improved 
somewhat in the box.

The negative voltage switcher of A15 board should be replaced with a 
suitable switcher, and some of the DC/DC switcher modules is built with 
isolation, so it should allow for mounting two in parallel such that you 
get both sides. PHK, have you checked this option?

Cheers,
Magnus