Are these hermetic? They don't look so.
What's the size?
And for those of us who don't have magic Palantir the meter is?
Sorry, but photos of setup, wiring and power source are mandatory for ppm healing by internet..
One thing that you may wish to observe is the Pomona cable/binding post combination. The cable plug insulation shells are spring loaded. I saw it happen that when inserted into the 3770 posts, the springs slowly pushed the plugs out of the posts. One would expect they don't, given this is same vendor.
What comes in mind secondly is external EMI interference. That is harder to trace though.
Are you willing to send your reference out? If so, I could stick it on my DMM7510 for a few days and see if its your environment or the reference itself.
Are you willing to send your reference out? If so, I could stick it on my DMM7510 for a few days and see if its your environment or the reference itself.
If nobody else has any ideas and it continues to spike like this I'd appreciate someone else checking it out so I might PM you about that.
Are you willing to send your reference out? If so, I could stick it on my DMM7510 for a few days and see if its your environment or the reference itself.
If nobody else has any ideas and it continues to spike like this I'd appreciate someone else checking it out so I might PM you about that.
Hello,
if I understand correctly, you have 2 PCBs ordered from that external company, which probably copied TiNs design (or whatever).
And both PCBs show these downward dips of several ppm?
time constants of these dips are several seconds, up to 30sec?
(Sorry, but proper scaling is missing in your diagrams)
Then these references really suffer from external EMI disturbances, as discussed intensively before, in this thread!
TiNs design is mostly a copy of the original LT schematic, and this is by design susceptible to EMI.
I have seen such dips also in both of my prototype LTZ1000 references, I think I already have published these old measurements somewhere here.. and these look very similar.
You can try to isolate your PCB by a steel box, or whatever you like, but EMI enters via power supply, or output jacks, no chance..
Even some of TiNs measurements (some unfiltered ones) on his own references show such dips.
The improvement for this problem is, either to use the Datron solution (for standalone reference 4910), implemented by Andreas.
Or you try adding 2 x 100nF foil capacitors in parallel to the 1k and 120 Ohm resistors, which will short these EMI spikes, which affect the sensitive BE diodes in either transistors of the LTZ1000, and will unlatch the oven regulation .
This simple measure improved my mentioned references a lot.
Anyhow, get rid of any SMPSUs in your lab!
Frank
No, no and no, putting capacitors across semiconductor junctions only transforms voltage spikes into current spikes and the microscopic matrices does not like that at all, it can even create cracks eventually but mostly decreases long term stability and increases noise. That is the last thing you want being fed into a reference zener, we have addressed this point before earlier in this thread.
Regarding the Linear Technology reference design, it is just that, it is a starting point from which the design engineer uses to refine, tweak and improve the design for their specific purpose. Authors have often pointed out that app notes are not finished complete designs but starting points that you have to finish for your own specific use. To wit, shielding a sensitive circuit from interference is something that you have to take care of and putting capacitors in the wrong places is not a fix, shielding requires the proper enclosure(s), often copper (or maybe aluminum) inside steel and sometimes mu metal around components, aluminum is not particularly effective in shielding on its own, I believe we also talked about this earlier. Improper construction techniques only adds to the problems and this includes connections to the outside world. Removing noise generating sources to farther away also reduces the garbage being injected into sensitive equipment, sometimes moving them further away won't work either if they're really noisy.....rule of thumb......always take care of noise at its source.
If you want a reference that provides the best possible long term stability then you're going to have to invest in doing things the right way and stop taking shortcuts that will affect long term stability even if you can't measure it today.
Theory about reference picking noise from power supply is easy to check - connect reference to +12V battery, like old one from car/motorcycle and log for few days.
Properly working ref should have stability within 0.2ppm. To remove DMM out of equation - use two references and connect them in opposition, so your Prema would only measure difference between REF1 and REF2 on most sensitive DCV range (100mV?).
No, no and no, putting capacitors across semiconductor junctions only transforms voltage spikes into current spikes and the microscopic matrices does not like that at all, it can even create cracks eventually but mostly decreases long term stability and increases noise. That is the last thing you want being fed into a reference zener, we have addressed this point before earlier in this thread.
I have to admit, I'm in Edwin's camp here on LTZ vs caps discussion. 3458A's A9 don't use magic caps either, for what it's worth (yes, not great design for long stability otherwise).
More often than not spikes and other instability is caused by measurement gear or wiring or environment (EMI/RFI/power coupling) than reference itself. Trying to make reference more robust against external world influence is kinda going backwards.