K. J. Lesker 800-Series Vacuum Gauge, KJL-902178
NO LONGER BEING SOLD, SEE EBAY
Lesker no longer sells these LED-display convection gauges, but plenty are on eBay in 2014. They employ a
convection gauge tube KJL-912161 or KJL-91216x, still sold at around $180, but occasionally seen for cheap on eBay.
The gauge tube is shielded 6-wire to an old-style octal socket. To verify a working tube, check the pins resistance using
the table in 5.2 of the operating instructions below.
NOTES:
The cables degraded in a lab environment, insulation turned crunchy, and I had trouble finding replacement shielded 6-cond.
Just buy some cheap DB-9 rs-232 cables w/shielding, snip off the connectors.
For calibration, see above PDF instructions section 4.5.
The 20-turn trimpot screw on the front meter face adjusts the 1-ATM value (760 Torr etc.) When adjusting this pot, the
gauge tube must be well warmed up, and clamped motionless and exactly horizontal, with connection port facing down.
Not in the instructions: the rear +8.8VDC trim-pot controls testpoint pin-3 on the
15-pin connector, with pin-4,5,7 being gnd reference. See pinout of DB-15 in sect. 4.4 table in above PDF.
On aging or corroded gauge tubes I found it impossible to zero the 2-torr adjustment for zero milliTorr.
Rather than buying expensive new gauge tubes, I set the 8.8VDC slightly high (8.9V.) Then while applying less
than 0.1 mT vacuum, set the *main* zero pot for slightly negative --5mT when the 2-torr zero trimmer is turned
all the way low. That lets me zero the displayed pressure using 2-Torr zero pot.
Seems to work so far. But I suspect that the 8.8V may affect the heater current in the platinum filament,
so it ?may? shorten the life of these already-aged gauge tubes.
