Agilent 34970A (34401A) self test error 606
Following the thread on time-nuts about the ebay seller yixunhk and afraid to
have been a victim of their way to do business, I decided to thoroughly test an
Agilent 34970A unit I bought from them some years ago in "almost-new" shape and
practically never used since then.
The 34970A is a data acquisition unit with builtin multimeter identical
to 34401A, with some math function absent in 34401A like the direct measurement
of RTDs. The ADC is a "Multislope III" and you may find it in other instruments
as well, like the E3631A power supply.
I took the opportunity to use it to watch the temperature of an experiment, so
I connected a 100R platinum RTD and begun.
After an hour I noticed a sudden 10x or more increase in noise, so much that
the measure could not be read easily while was still to the tenth of C just
a moment before.
After having excluded cabling pickup, sensor defects, and so on, I launched the
self-test and got Error 606.
I left the instrument on for a full day, to let it stabilize and maybe dry up
from the moisture, even if it has always been kept in the lab, and repeated
the test with the same error. The test imply a power cycle and the error
didn't wanished just with that.
Today I was ready to do further checks, but after a cold start, the noise is
normal (I think, being +-17PPM worst case in the two wire 100R range measuring
a 100R precision resistor at 6.5 digits resolution) and the self test pass.
(the 34401A noise with the same resistor is much better, +-2.5PPM worst case,
but I expected this because of relays in switch units and wiring issues in my