INFICON PLO-10i Phase Lock Oscillator - Manual (Page 29)

PLO-10 PHASE LOCK OSCILLATOR
ADJUSTING THE CAPACITANCE CANCELLATION 4-3
this is not the point you want. Back off the course adjustment until the flashing begins
again, then continue to the point where the flashing just stops. The course adjustment is
now complete.
Install a crystal into the holder. Now depress and hold the Reset button. Slowly adjust
the fine trimmer clockwise until the flashing of the Sweep LED begins again and then
back off until it just stops. The capacitance compensation adjustment is now complete.
Release the Reset button and assuming the crystal is not dead or out of range, the PLO-10
will lock on it.
4.2 WORKING WITH VERY LOW Q CRYSTALS
Very low Q crystals require very close adjustment of the compensating capacitance to
insure a successful lock. To adjust the compensation capacitance one pushes the Reset
button and adjusts the capacitance to the point where the Sweep LED just ceases to flash.
With very low Q crystals, the PLO may not lock upon release of the Reset button. The
Unlock LED will be on and the Sweep LED will be flashing. This is normal. Even so it
may be possible to lock on the crystal by slowly adjusting the fine capacitance
counterclockwise until the Sweep LED again ceases to flash. Lock is evidenced by the
Lock LED turning on or by a value of greater than 8 millivolts at the Conductance output.
Once lock is achieved the true series resonant point can be found by adjusting the
capacitance for maximum conductance. The limits of the crystal bandwidth can be
determined by adjusting the capacitance and reading the maximum frequency and the
minimum frequency just before the PLO loses lock.