INFICON RQCM - Quartz Crystal Microbalance Research System - Manual (Page 51)

RQCM – RESEARCH QUARTZ CRYSTAL MICROBALANCE
CRYSTALS, HOLDERS AND FLOW CELL 4-13
o
Remove the crystal to expose the crystal cavity.
o
Remove both Pogo® contact pins from their sockets. Use a pair of tweezers (or
gloved fingernail), grab the Pogo® head firmly and pull it straight out of its
socket.
o
Rinse the holder, the crystal cavity and the Pogo® sockets generously with
deionized water to remove all traces of chemicals and thoroughly blow-dry the
whole holder using filtered air. Ensure all liquids that may have been trapped
inside the sockets are removed.
o
Generously rinse the Pogo® contact pins with deionized water, occasionally
squeeze the pins to push out any liquids that may have been trapped inside the
pins. Thoroughly blow-dry the pins using filtered air.
o
Install the Pogo® pins back into their sockets. Use the tip of a pair of tweezers
and push down on each Pogo® pins to verify their deflection.
4.3.3 CONSIDERATIONS FOR BUILDING YOUR OWN HOLDER
You MUST consider the following aspects when building your own crystal holder.
The holder must be designed so that when a crystal is installed, the its front electrode (sensing
electrode) is connected to the housing (shell) of the SMB Crystal Connector on the RQCM (see
Section 3.3.5); and the rear electrode is connected to the center pin of the SMB Crystal
Connector.
The crystal should be clamped, as close as possible, to the edge of the crystal to avoid damping of
the crystal’s oscillations.
The holder clamping mechanism should have a positive stop to avoid excessive clamping force
on the crystal.
If the crystal is to be used in a conductive fluid or conductive gas, the rear electrode must be
sealed from the conductive environment to avoid an electrical short between the electrodes. The
electrodes should be designed so the rear electrode and the electrodes contacts can be sealed.
Only the front electrode should be exposed.
The connecting cable must be coaxial all the way, from SMB on the RQCM, on up to the crystal.
The shield of the coaxial must connect to the front electrode and the center conductor must
connect to the rear electrode of the crystal. In addition, the coaxial cable must be free of kinks,
knots, etc. to avoid unbalanced capacitance in the cable. Note that a one-foot of well balance
RG174A/U coaxial cable has approximately 29 picofarads.
The total capacitance of the crystal, the crystal holder and the cable must be within the RQCM’s
capacitance compensation limits (between 40 and 200 pfd).
4.4 FLOW CELL
The FC-550 Flow Cell is designed to be used with any of INFICON's 100 series crystal holders.
The FC-550 is made from Kynar®. The cell has two stainless steel inlet and outlet tubes with a
.047” I.D. x .062” O.D., compatible with 0.062” I.D. tubing. A Viton® O-ring provides sealing
between the cell and the face of the sensor crystal. The cell is used in place of the Crystal
Retainer Ring. Once installed in a probe, it creates a flow chamber of approximately 0.1 mL.