INFICON RQCM - Quartz Crystal Microbalance Research System - Manual (Page 26)

RQCM – RESEARCH QUARTZ CRYSTAL MICROBALANCE
OPERATION 3-2
3.2 UNDERSTANDING AND SETTING UP A CRYSTAL MEASUREMENT
CHANNEL
The RQCM can have up to three independent crystal measurement channels. Each channel has a
crystal input, three status LED’s, fine and course capacitance adjustments, a reset switch and a
crystal face connection. Refer to Figure 2.
3.3 FRONT PANEL DESCRIPTION
3.3.1 LOCK INDICATOR
The green, Lock LED is on when the oscillator is locked on a crystal’s resonant frequency.
3.3.2 UNLOCK INDICATOR
The Red, Unlock LED will be on whenever the oscillator is not locked on a crystal.
3.3.3 SWEEP INDICATOR
The Yellow, Sweep LED flashes each time the frequency ramp is reset to its low starting point.
In normal operation, the sweep light will only flash while adjusting the capacitance
compensation. The Sweep LED will not light when locked on a crystal.
3.3.4 RESET SWITCH
The Reset switch should be pressed while adjusting the capacitance compensation. This switch
forces the VCO to its lowest frequency independently of the Integrator output. The Reset switch
also forces the Lock LED on, thus turning off the quadrature current injection which is required
for proper capacitance cancellation adjustment. The equivalent of about 1.5 pfd of capacitance is
added as quadrature current to insure that the VCO ramps up in frequency when not locked onto a
crystal. The quadrature current is turned off as soon as a lock is detected.
3.3.5 CRYSTAL CONNECTOR
The SMB connector labeled Crystal provides connections to the crystal. When used with a INFICON
crystal holder, the center pin connects to the crystal’s rear electrode, and the connector
housing connects to the crystal’s front electrode.
3.3.6 CRYSTAL FACE CONNECTOR
The Crystal Face connector provides a direct connection to the crystal’s front electrode. Note that
the mating connector (2.5 mm male plug) provided with each Crystal Measurement Channel must
be used for proper connection. When the mating connector is inserted, the crystal face electrode
is galvanically (transformer) isolated from earth ground allowing a potential to be applied. Use
this connection to connect the crystal face electrode to the working electrode of a potentiostat or
galvanostat for electrochemical experiments. When this connection is not in use, the crystal face
electrode is grounded to minimize effects of capacitance that may couple to crystal face electrode
in non-electrochemical experiments.