-------- I had this morning, and put it into action right away:
I disconnected the A15R8 resistor from the tempco afflicted A15CR5 zener diode, and hooked it up to my Fluke 732A's 10V output (which is speced to 10mA). I had expected to see a vast improvement in C-field drive stability, but while the improvement is measurable, it is a lot less than I had expected. Having eliminted that one, there are two influences left: * Noise from the +20 V supply leaks through The data evidently shows this to be the case, but the correlation does not explain all the C-field current variability. * Tempco in the constant current driver circuitry I'm increasingly leaning this way, because even though A15R8 is fed from the rock-stable Fluke, the voltage at the A15Q6A base still varies quite a lot with temperature, but the short term jitter is much better. I don't have enough data yet to conclude if the MVAR floor is improved, but it looks quite promising so far: The curve has very confidently dipped below 1e-13 at 5000 seconds. It used to flatten at 3e-13. Next experiment is going to be driving the C-field solenoid directly from the Fluke 732A through a suitable low tempco current-limiting series resistor. Anybody want to bet what *that* will do to the MVAR floor ? I'll write this up on my web-pages once I have more data. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [email protected] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
