INFICON RQCM - Quartz Crystal Microbalance Research System - Manual (Page 72)

RQCM – RESEARCH QUARTZ CRYSTAL MICROBALANCE
THEORY OF OPERATION 5-20
V
oc
= Open Circuit crystal drive voltage = 125 mV
R
s
= Crystal drive source resistance = 20 ohms
R
cry
= Crystal resistance value in ohms
Examples:
1.
Crystal Resistance = 80 ohms
P
cry, in watts
= [0.125/(20 + 80)] 2 * 80 = 1.25E -4 watts or 125 µW
2. Crystal Resistance = 4000 Ω
P
cry, in watts
= [0.125/(20 + 4000)] 2 * 4000 = 3.87E -6 watts or 3.87 µW
Figure 27 Crystal Power Dissipation vs. Crystal Resistance
Crystal Power vs. Crystal Resistance
0
50
100
150
200
250
10000
456 224 144 103
79 63 51 42 35 30 25 21 18 16 13 11
9 8 6 5
Crystal Resistance (ohms)
Crystal Power (uW)