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Chemistry Electronics Services
ARCHIVE OF REPAIR TRICKS, USEFUL INFO, ETC.


Repairing Vacuum Gauge, KJ Lesker KJL-205, Glassman


TYPICAL VALUES

Op amp gain: 500x
Output jack at 1ATM: 4.87Vdc
Gauge tube DV-6 thermocouple output:
- 10mV at full vacuum (DC on gauge tube pins 3,7)
- 0.61mV at 760Torr, 1ATM
Analog meter: 1mA, 1V F.S., 995ohm
Filament: 18ohm (gauge tube pins 3,5)
Filament drive: 1.18Vpp square wave, 880Hz (Trimmer max 1.25Vpp, set by 20-turn trim pot screw)
Pot 1-turn Meter-adj: set 390 ohms, in series with 3.47K
Pot 1-turn Gain-adj : 69K ohms (in series 937K for 500x op amp gain)
Pot 1-turn 10mV ref : 9.95mV
147VAC across ballast cap (if 118VAC line volt)
43.8VAC at pwr xfrmr primary (if 118VAC linevolt)
23.2VAC pwr xfrmr AC out (if 118VAC linevolt)


Internal power supplies:

  • 23.2VAC ct xfrmr out (at 118VAC line)
  • +11.6V unreg
  • -12.6V unreg
  • +6.9V zener
  • -6.07V zener
  • +4V (approx.,), adj. regulator (fil. drive)






SETTINGS:

  • With power off, first set the mechanical meter-zero (black screw below meter face.)
  • R1 - Filament drive voltage, set for square wave 760mVpp (380mVrms) across gauge pins 3,5.
  • R2 - Zero pot (10mV reference adj,) set for 10mVDC between meter-neg (common) and IC pin-3.
  • R3 - Span pot, set to give 5.0VDC at Vout jack during 1ATM pressure.
  • R4 - Meter adj pot, set to give 1ATM meter reading during 1ATM pressure
  • For new gauge tube, apply < 0.1 millitorr pressure, tweak R1 for zero reading.

For aged or contaminated gauge tubes where R1 cannot set the filament temp high
enough to reach meter zero, turn R1 down to 90% of max, then tweak R2 to give a
zero pressure reading while 0.1 mT is applied to gauge tube (or, set R2 to produce
9.5mVDC or lower on IC pin-3.) Then with 1ATM applied to gauge tube, tweak
R3 to give 1ATM meter reading.


See also: Gauge tube pinouts
Created and maintained by Bill Beaty.

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University of Washington
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