INFICON RQCM - Quartz Crystal Microbalance Research System - Manual (Page 34)

RQCM – RESEARCH QUARTZ CRYSTAL MICROBALANCE
OPERATION 3-10
drift is temperature. Review section 4.1.9 for more information on the crystal’s response to
temperature.
3.9.3.1 Operate at or Near The Crystal’s “Turn-Around-Point”
When possible, perform the experiment at the sensor crystal’s “turn-around-point”. At or near
this temperature, most of the errors due to temperature are negligible. 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’s 1
inch crystals are optimized for two operating temperatures namely 90ºC and 25ºC.
3.9.3.2 Control The Temperature
If operation at or near the crystal’s zero turn-around-point is not possible, the operating
temperature should be controlled within a degree or a fraction of a degree of its desired value.
How tightly the temperature should be controlled depends on how far the operating temperature is
from the zero turn-around-point, the further away from the turn-around-point, the larger the error.
For example, for 90ºC-cut-crystal, about 1.5 Hz/ºC error is expected if operating at 80ºC.
However, as much as 5 Hz/ºC error is expected when operating at 60ºC.
3.9.3.3 Keep the Test Chamber Clean
Keep the test chamber clean, as any particle attached to the crystal’s sensing surface will result in
a frequency change.
3.9.3.4 Keep a Constant Gas Flow
If a gas is used, keep the flow constant throughout the experiment. The crystal’s frequency is
also sensitive to changes in pressure, which will result, if the flow rate is not constant.
3.9.4 FOR OPERATION IN LIQUIDS
Since the sensor crystal is dampened by the liquid, any error in the measurements will be
amplified. Extra care must be taken to ensure minimal error. The sample liquid should be
prepared carefully. Changes in temperature or the properties of the solvent as well as air bubbles
will affect the sensor signal.
3.9.4.1 Degas The Sample Liquid
The sample liquid should be degassed prior to measurement to avoid the formation of air bubbles
on the surface of the crystal.
3.9.4.2 Wait For Mechanical Disturbances To Stabilize
To minimize random fluctuations cause by vibrations, it is best to immerse the holder, with a
crystal installed, in the sample solution several hours before the experiment is started.
3.9.4.3 Wait For The Temperature To Stabilize
To avoid the formation of air bubbles and reduce temperature related artifacts, the sample liquid
should have approximately the same temperature as the measurement chamber’s working
temperature (±2°C). Wait at least one hour after a holder is immersed in a liquid to allow for the
crystal to come to equilibrium, before performing any accurate measurements.