Here I have some pictures and the schematics of my crude prototype which I had with me at the Metrology Meeting.
And when I was going to do some measurements together with HighVoltage, it failed. Reason: for any unknown reason
the B-E diode of the 2N2219A became high-impedance. No idea why. I changed the transistor and everything
is nice and dandy since then.
Ok, as promised, here are some pictures.
Let's start with the schematics, made with a high sophisticated CAD system
This is the Bopla plastic case opened. On the top right there is one of two
Makita 18V LiIon batteries, used for the power supply. In the socket,
there is a 15V LDO from TI.
This is the on/off switching, realized with a latching relay and some reed sensors.
Also some filtering with Wima capacitors on the left.
This is the ground plane, made of 1mm copper.
Inner case opened and overview:
Detail view of the LT1028 and the air wiring (no need of guardening the lines)
Detail view of the LTFLU-1 in it's socket (coming from Fischer electronic, they are also doing cases)
The yellow resistors were made by forum fellow Edwin G. Pettis. Thanks again for the really fast delivery.
Detail view of the outgoing binding posts:
And here I've assembled the reference prototype with my resistor decade (top left),
the GW121 measuring the air temperature and the DMM 7510
It is continously drifting upwards. I think, the main reasons for this is:
- too short power on time, so it did not found its thermal balance
- I did not set up the tempco point of the LTFLU-1, this is the next thing on my list.
- my bizarre resistance decade box is probably not the best in respect of thermal drift
These are the settings used for the measure:
More to come, but don't know, when.
Next step is getting the 0.something ppm tempco point.
Will let you know about my (probably slow) progress.
Best regards,
Andreas
Edit: some typos