Hello Hendrik,
the first what I would do is some qualification measurements:
since the pricing within the bay is lower as on original manufacturer
they might either be recycled parts or the remaining parts after selection
for instruments.
On my references I did the following tests:
- noise (does it have the 1.2uVpp?)
- temperature test: how large is the temperature drift
if you have a temperature chamber this will ease the test.
I only have a thermoelectric cooling / heating box for around 10-40°
centigrade.
- Temperature setpoint test: how large is the tempco of the unstabilized
reference if you do a 10 degree setpoint offset.
(is usually around 50ppm/K)
- Power supply voltage rejection test
- Influence on EMC (sensibility on capacitive influence by your hand)
- Tilt test (described here from Frank)
I hope that I didnt miss any...
Did you already clean the pcb?
Did you pre-age the resistors before mounting?
Is the LT1013 within a hermetically housing?
After qualification tests and if I had a thermal chamber
I would first do some pre-ageing (thermal cycling) for at least 1-2 weeks
with daily measurement of the voltage.
After this at least further 1000-4000 hours continuously powered to
stabilize.
measurements for a few days, although I think that the drift+noise from
the HP reference and my LTZ are quite close
But: the HP reference has already stabilized and is not freshly soldered.
I would do a final calibration after around 6 months continuously operation.
And if you populate the 2nd PCB you can make difference measurements
in a voltage range with higher resolution on your HP3456 (perhaps 0.1uV in
200mV range).
With best regards
Andreas
----- Original Message -----
From: "Hendrik Dietrich" <[email protected]>
To: <[email protected]>
Sent: Saturday, March 02, 2013 10:14 AM
Subject: [volt-nuts] A new LTZ1000A transfer standard is born
Good morning fellow nuts,
after a short planning and long wait times to get LTZ from china[1], PCB
from the Ruhr valley[2] and resistors from the UK[3], I was no longer
able to wait and slap everything together.
It is a clone of the Williams design in Linear Technology AN86 with
2x25K in parallel as R4, as suggested by Dr. Frank Stellmach from this
maillist. The interesting resistors are General Resistance Econistors,
the zener plus is buffered with a further LT1013 before breakout with
4mm copper-tellur receptacles[4]. The LTZ1000A has a hat made from a
little plastic cap and a o-ring to fix it to the LTZ case. The positive
and negative out and also a hole for a guard are on a slotted part of
the PCB and around the LTZ I spent some holes to give it a bit of
stress-relief.
It worked instantly, I didn't even try step-by-step startup, current
limiting was the only safety measure. No stability measurements yet, but
the HP34401A at work (where I soldered it during lunch break) and the
HP3456A at home have shown the same voltage (the 3456A is calibrated
against my work DMM).
After finishing the circuit board, I have put it into a tinned sheet
iron case[5] and made a makeshift thermoinsulation from bubble wrap and
a cardboard box. Result:
http://primeintrag.org/LTZ1000A.JPG
that is the newborn and one of the spare PCBs.
Planned next steps, any hints?
0. Keep it on the HP3456A today and watch infrequently and hope that
only the last digit might change
1. Put it in the thermal chamber at work (hot-cold-hot cycle, tmax=80°C)
2. keep it powered for a few weeks
3. Hook it to my 3456A and use EZGPIB to get some voltage-over-time
measurements for a few days, although I think that the drift+noise from
the HP reference and my LTZ are quite close
4. Beg a cal lab to do a un-accredited HP3458 measurement with results
written on a napkin to get a number! (Repeat after a year or so)
Regards
Hendrik
[1] ebay seller polida 2088
[2] http://www.fischer-leiterplatten.de
[3] http://www.rhopointgermany.com/
[4] http://www.multi-contact.de/
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