INFICON PLO-10i Phase Lock Oscillator - Manual (Page 53)

PLO-10 PHASE LOCK OSCILLATOR
THEORY OF OPERATION 8-5
Where:
R
∆ = change in series resonance resistance in Ω,
r
A
= active area of INFICON 1-inch crystal = 3.419×10 -5 m 2
26
e
= piezoelectric constant for an AT cut quartz = 0.095 kg/sec 2 /V
For example, moving the crystal from air to pure water @ 20°C, Equation 7 and Equation
8 predict a decrease in f of 714 Hz and an increase in R of 357.4 Ω, respectively. Note
that at pure water @ 20°C has a density (ρ
L
) of 998.2 kg/m 3 , and a viscosity (η
L
) of
1.002×10 -3 N · sec/m 2 .
Excellent agreement between the frequency and resistance equations and the
experimental results has been proved 24 25 26 , making the QCM an excellent tool for the
evaluation of fluid properties. Application examples include in-situ monitoring of
lubricant and petroleum properties 27 . The tight correspondence between theory (Equation
7 and Equation 8) and the PLO is clearly illustrated by Figure 16 and Figure 17,
respectively. Note that some of the discrepancy in the resistance curve could arise from
an error in estimating the active electrode area.
The PLO-10 utilizes the PLO technology which allows the sensor crystal to operate under
heavy viscous loading. INFICON Crystal Holders support operation in gas and liquid
environments and provide single-electrode exposure to liquids as required for
compatibility with electrochemical QCM measurements. The PLO-10 will maintain
oscillation up to a series resonance resistance of about 5 kΩ. It will support crystal
operation in highly viscous solutions up to 88% weight percentage of glycerol 28 .