INFICON RQCM - Quartz Crystal Microbalance Research System - Manual (Page 30)

RQCM – RESEARCH QUARTZ CRYSTAL MICROBALANCE
OPERATION 3-6
the SMB connector labeled Crystal but don’t install a crystal.
If the Sweep LED is flashing, press and hold the Reset button and then turn the fine trimmer
clockwise until it just stops flashing. Go back and forth a few times to get a feel for the point
where the Sweep LED just stops flashing. Release the Reset button and the Sweep LED should
begin to flash again.
Install a crystal. The PLO should lock. Even so, press and hold the Reset button and again adjust
the fine trimmer to the point where the flashing just stops. The capacitance cancellation
adjustment is now perfect. Remember to check this adjustment whenever the crystal’s
environment changes.
If you could not find the proper zero capacitance point using the fine trimmer alone, then the
coarse rotary switch needs to be adjusted. Follow the instructions below to set the coarse rotary
switch.
First adjust the fine trimmer so that it is 50% meshed and the rotor plates are below the shaft.
You can see these plates through the oversize adjustment hole. See Figure 3. Next connect a
cable and crystal holder, and the crystal, if you haven’t already done so.
Figure 3 Capacitance Adjustments
Set the course rotary switch to its minimum. Depress the Reset button, and observe the yellow,
Sweep, LED. It should be flashing very fast, indicating the capacitance is grossly under
compensated. Now rotate the course switch clockwise, one step at a time. At each stop observe
the yellow, Sweep, LED, at some point it will cease to flash. Back off one stop so the flashing
begins again. The course adjustment is complete.
Slowly adjust the fine trimmer clockwise (increasing capacitance) until the flashing of the Sweep
LED just stops. The capacitance compensation adjustment is now complete. Release the Reset
button and assuming the crystal is not dead or out of range, the RQCM will lock on it.
3.5.1 AS A GENERAL RULE
♦ The Reset switch must be depressed during the adjustment for capacitance cancellation.
♦ Capacitance cancellation is essential for accurate measurements of liquids and lossy (soft)