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D.2 Adjustment of Pump Volume
The micro pump delivers droplets in steps of 0,5 µl and for a target volume of 4,0 µl the pump will
make eight pump movements. The Static Mode can be used to measure the average volume from six
droplets applied on a non-absorbent specimen surface (e.g. a metal foil or a glass plate). The volume
readings will vary around an average and should not show an increasing trend indicating air bubbles in
the liquid system.
Two numbers describe the pump performance where
- “repeatability” is the variation in droplet volumes around the average of six volume determinations;
- “deviation” is the difference between the target volume (e.g. 4,0 µl) and the average from the six
volume determinations (e.g. 4,1 µL).
The “repeatability” is a function of the pump and cannot be adjusted. This value should not exceed 5%
(corresponding to ±0,2 µl at a target of 4,0 µl).
The “deviation” is a function of the physical dimensions of the pump tubing. This value should not
exceed 5% (corresponding to ±0,2 µl at a target of 4,0 µl). If the average volume from six droplets is
outside 5% from the target, the droplet size can be adjusted with the procedure described below.
a)
Locate the volume adjustment knob located on the pump lid (A in Figure D-2).
b)
When the droplet volume is
too high
, turn knob in a counter clockwise direction.
When the droplet volume is
too low
, turn the knob in a clockwise direction.
c)
Take a new set of readings in Static Mode and check the average volume from six droplets.
If necessary repeat step (b) above.
D.3 Small droplets below 0.5 µl
The micro pump delivers droplets in steps of 0,5 µl but to measure SuperLow contact angles it might
be necessary to use even smaller droplets. Turn the volume adjustment knob (A in Fig D-2) counter
clockwise for a smaller volume. Apply a few droplets on a smooth, reflecting glass surface and
determine the set volume in Static Mode.
In SuperLow Mode enter the determined volume into the Volume field (default 0.25 µl) before the
measurement is carried out.
Remember to reset the volume adjustment knob (A) to 0.5 µl when leaving SuperLow Mode.
PGX+ User’s Manual 4.0g /ENG
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