HP5065A environmental sensitivities
In message B1C92A76-2349-48DB-9FA5-F95F5D31AB02@n1k.org, Bob Camp writes:
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.
That's only part of it.
The rather important zener diode regulating the C-field is located
on the DC regulator board, where the temperature depends directly
on the grid voltage...
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Hi Bob,
On 05/22/2016 05:21 PM, Bob Camp wrote:
Hi
On May 22, 2016, at 10:49 AM, Attila Kinali attila@kinali.ch wrote:
Hoi Poul-Henning,
On Fri, 20 May 2016 09:52:39 +0000
"Poul-Henning Kamp" phk@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
Hi
In 40 years of getting phone calls, the one that never seems to go away starts out with:
“We … errr… measured the temperature rise in our box and need to adjust the upper end
temperature on your part”.
The really interesting part is that you can get multiple calls that go the same way from the
same engineering team. Each time they drop in another board or check a rack in a customer
installation new data arrives …
A 5C rise is nothing. Some of these boxes run at 95C with what is supposed to be 50C inlet air.
Bob
On May 22, 2016, at 12:33 PM, Poul-Henning Kamp phk@phk.freebsd.dk wrote:
In message B1C92A76-2349-48DB-9FA5-F95F5D31AB02@n1k.org, Bob Camp writes:
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.
That's only part of it.
The rather important zener diode regulating the C-field is located
on the DC regulator board, where the temperature depends directly
on the grid voltage...
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
In message 02878E59-0BAE-4220-8A86-5E59F0CA5F44@n1k.org, Bob Camp writes:
'We ... errr... measured the temperature rise in our box and need to adjust
the upper end temperature on your part'.
yeah, I know that story:
http://phk.freebsd.dk/hotsun/
That's the CPU/fan cover for a SUN Ultrasparc/60 where the fan connector
was not reattached after somebody messed with it...
What surprises me about the HP5065 is that they could quite easily have
done better than they did, but I suspect they had to make sure the specs
were meaningfully worse than the HP5061...
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
In message 5741E08B.9080706@rubidium.dyndns.org, Magnus Danielson writes:
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?
Yes and no.
I think the +/- 20V should not matter, and the reason they currently do
is something a couple of well-chosen modern op-amps can take care of as
far as I can tell.
My hope was to design a couple of plug-in replacement boards to fix most
of these issues, while allowing A/B comparisons to the improvement can
actually be measured.
Basically:
A new integrator board, using a modern chopper/zero-drift op-amp.
A new AC amplifier, ditto.
Instead of the two diodes, put a modern "ideal diode" circuit and
two DC/DC converters on the first PSU board, producing the +24V and
a -15V rail for the rest of the instrument. (-15 instead of -20 since
it will be driving the opamps mentioned above.
On the second board, an opamp to drive the existing chassis-mounted
+20V series transistor from a really good voltage reference (LM399)
and the most stable C-field drive circuit I can come up with.
But as I said, I'm just about to start building a new house, so my
time is limited for the next year or so...
If somebody else wants to take the lead, I'll happily assist as I can...
The "NextGen" project, would be to use a 48bit DDS chip to generate
the 60+MHz drive signal for the microwave, and a "geophone" ADC chip
to detect the modulation from the photo-diode, but that is even further
out...
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
On 5/22/16 10:25 AM, Bob Camp wrote:
Hi
In 40 years of getting phone calls, the one that never seems to go away starts out with:
“We … errr… measured the temperature rise in our box and need to adjust the upper end
temperature on your part”.
Or, as a designer using an OCXO part, you have to explain to the
reviewer that just because, after updating the thermal model, the
temperature at the part is now 50C instead of 40C, it probably doesn't
matter, because inside the OCXO's oven, it's even hotter. Or, even
worse, that the power dissipation goes down as the outside temperature
goes up.