INFICON PLO-10i Phase Lock Oscillator - Manual (Page 15)

PLO-10 PHASE LOCK OSCILLATOR
GENERAL DESCRIPTION 1-5
1.2.4 CONDUCTANCE ERRORS
Conductance measurements are meaningful over the range of 0.0001 to 0.04
siemens (a crystal resistance of 10 KΩ to 5 Ω). Two characteristics of the PLO
limit the range of the conductance measurement. The first is the zero drift of the
demodulator and amplifier and determines the minimum measure-able
conductance. This drift can amount to 0.00005 siemens. The second
characteristic is the non-zero source impedance of the crystal drive voltage. This
source impedance, 20 Ω , appears in series with the crystal resistance and the
conductance output is proportional to the conductance of the crystal and source
combination. The equation for crystal resistance is:
Rcry = (100/Vcond) -20