INFICON PLO-10i Phase Lock Oscillator - Manual (Page 19)

PLO-10 PHASE LOCK OSCILLATOR
UNDERSTANDING AND SETTING UP THE INFICON PLO-10 2-1
2 UNDERSTANDING AND SETTING UP THE INFICON PLO-10
There are several LED’s on the PLO-10 to indicate its operation.
The green, Lock LED is on when the frequency is locked to a connected crystal’s
resonant frequency.
The Red, Unlock LED will be on whenever the frequency is not locked.
The Yellow, Sweep Rate LED flashes each time the frequency ramp is reset to its low
starting point.
The Reset switch allows you to force the VCO to its lowest frequency independently of
the Integrator output. The Reset switch also forces the Lock LED on, thus turning off the
quadrature current injection. The Quadrature current injection must be off to properly
adjust the capacitance cancellation. To insure that the VCO ramps up in frequency, a
small amount of quadrature current is injected into the current to voltage buffer whenever
the PLO is unlocked. This current is equivalent to a shunt capacitance of about 1.5 pfd.
As soon as lock is detected, the quadrature current is turned off.
2.1 NORMAL OPERATION
The PLO-10 comes set up for operation with a INFICON cable and crystal holder. If a
INFICON
cable and crystal holder is being used, then no initial adjustments should be
needed.
During normal operation with a crystal installed and connected to the oscillator, the green
Lock LED will be on and the frequency output will reflect the crystal resonance. The red
Unlock LED will be off.
If the Unlock LED is on, the Sweep Rate LED should slowly flash. Continuous
sweeping of the frequency range indicates that the crystal’s resonant frequency is outside
of the PLO’s frequency range or the crystal’s conductance is below the conductance
threshold.
No flashing of the Sweep Rate LED when the Unlock LED is on can mean one of two
things. First, if the VCO frequency is sitting at its low limit, it means the electrode
capacitance is over compensated. Second, in some cases, even though the crystal
conductance has fallen below the threshold necessary to indicate lock, the internal signals
are still sufficient to keep the VCO locked to the crystal. In that case, the PLO really is
locked and the VCO frequency will be sitting at the crystal frequency somewhere
between its minimum and maximum frequencies.
If the VCO frequency is sitting at its low limit, press and hold the Reset switch and adjust
the fine capacitance trimmer a few degrees clockwise (not more than ten) until the Reset
LED begins to flash.
2.2 CHECKOUT
Make sure the wall mount power supply is specified for the voltage in your lab (120/240
volts).