INFICON PLO-10i Phase Lock Oscillator - Manual (Page 40)

PLO-10 PHASE LOCK OSCILLATOR
CRYSTALS, HOLDERS AND FLOW CELL 7-6
frequency of a sensor crystal on temperature is generally small in experiments in gas
phase when operating at or near its “turn-around-point”. The “turn-around-point” is
where the temperature coefficient of the crystal is zero. That is, there is no change in
resonance frequency due to a change in the temperature of the crystal at the turnaround
point. INFICON 1 inch crystals are optimized for two operating temperatures namely 90ºC
and 25ºC. These crystals have very good temperature stability when operating close to
their specified temperature.
Even though AT cut crystals are designed to minimize the change in frequency due to
temperature, the effect of temperature can be significant when attempting to resolve small
mass (frequency) changes over long periods of time. This frequency change due to
temperature is magnified when the sensor crystal is submerged in liquids. This is due to
the coupling of the shear mode oscillation with the temperature dependent viscosity and
density of the fluid. For experiments in liquid phase in which the frequency is to be
monitored over long periods of time, the temperature must be controlled to at least 0.1°C,
and preferably better. In electrochemical experiments this is often achieved with
temperature controlled baths and jacketed cells. It is always good practice to wait at least
30 minutes before performing any accurate measurements after the crystal comes in
contact with a new medium. This allows the crystal to come to equilibrium with the
medium. If temperature control is not possible or practical, attempts should be made to
measure the temperature of the solution around the crystal during the experiments and
perform temperature compensation.
In short, each PLO-10 user must determine the effect of temperature on the experiments
being performed and either control the temperature accordingly, or measure the
temperature and compensate for it.
Freq Change vs. Temp
INFICON
AT cut for 90C
-250
-225
-200
-175
-150
-125
-100
-75
-50
-25
0
25
50
75
100
125
150
175
0 10 20 30 40 50 60 70 80 90 100 110 120
Temperature (C)
Delta Frequency (Hz)