INFICON PLO-10i Phase Lock Oscillator - Manual (Page 25)

PLO-10 PHASE LOCK OSCILLATOR
CALCULATING CRYSTAL RESISTANCE 3-1
3 CALCULATING CRYSTAL RESISTANCE
The PLO-10 provides a dc output voltage proportional to conductance. Conductance is
the inverse of Resistance. Thus, Conductance = 1/Resistance or Resistance =
1/Conductance. The units of resistance are ohms (volts per ampere) and the units of
conductance are siemens (amperes per volt). The PLO-10 Conductance Output is
inversely proportional to the sum of the crystal resistance plus the Crystal Drive Voltage
source resistance. Thus,
Conductance Output = 100/(R
cry +
R
source
).
The Conductance Output scaling is 100 volts per siemen. Solving for R
cry
,
R
cry
= (100/Conductance in volts) - R
source
The Crystal Drive Source Resistance is 20 Ω, so
R
cry
, in ohms = (100/Conductance, in volts) – 20 Ω
Examples:
1.
Conductance output voltage = 1.000 volt.
R
cry
, in ohms = (100/1.000) – 20 = 80 Ω
2. Conductance output voltage = 0.015 volts.
R
cry
, in ohms = (100/0.015) – 20 = 6667 – 20 = 6647 Ω = 6.647 KΩ
R esistance vs. Voltage
1.00
10.00
100.00
1000.00
10000.00
0.
00
0.
25
0.
50
0.
75
1.
00
1.
25
1.
50
1.
75
2.
00
2.
25
2.
50
2.
75
3.
00
3.
25
3.
50
3.
75
4.
00
Conductance Voltage (V)
Equivalent Resistance (R)
Figure 5 Resistance vs. Conductance Voltage