Quartz Crystal Microbalance Digital Controller

30 Theory, Operation and Calibration Chapter 2WhereR = change in series resonance resistance in ,n = number of sides in contact with liquid, s = angular frequency at series resonance (2 f s ),L u = inductance for the unperturbed (dry) resonator, usually in mH.The QCM200 System was specifically designed for operation under heavy viscousloading. The standard Crystal Holder supports operation in gas and liquid environments,and provides single-electrode exposure to liquids 17 (i.e. n = 1 in eqn. 16) as required forcompatibility with electrochemical QCM measurements. The Crystal Oscillator providesboth frequency and resistance change signals and will maintain oscillation up to a seriesresonance resistance of about 5 k (it will support crystal operation in highly viscoussolutions up to 88% (w/w) glycerol in water). Transformer isolation of the oscillatorcircuit provides compatibility with virtually any potentiostat.As an example, eqn. 15 predicts a decrease in f 0 of 715 Hz on transfer from vacuum topure water 18 at 20°C, in agreement with the results observed with a QCM200 using 1 inchdiameter, polished, gold coated, 5 MHz crystals, mounted on a standard Crystal Holder.Excellent agreement between the frequency and resistance equations and theexperimental results has been proved 19 , making the QCM an excellent tool for theevaluation of fluid properties. Application examples include in situ monitoring oflubricant and petroleum properties 20 . The tight correspondence between theory (eqns. 15& 16) and experiment is clearly illustrated by Figure 22.QCM200 Quartz Crystal Microbalance