TIP TO SURFACE SPACING FOR OPTIMUM DISPENSING

摘要

Perfusion is a well-known problem associated with dispensing apparatus. Although various techniques are known to remove some of the problems associated with perfusion, there is still a problem when the liquid to be dispensed needs to be dispensed onto a surface, for example the surface of a test element, as a steady stream. In this case, the stream must be controllable as perfusion is obtained when it proceeds too fast causing puddling on the test element surface. Furthermore, if the stream is too slow, it may break up into droplets which spatter on impact with the surface producing other problems. Described herein is a method for automatically adjusting a dispensing tip (30, 34) to be at a proper distance from a surface (37) onto which liquid is to be dispensed which precludes the dispensing stream from puddling up or from breaking apart. The method features the formation on the tip (30, 34) of a meniscus (m) of a nominal small volume and advancing the dispensing tip (30, 34) and meniscus (m) until the surface (37) is contacted. The resulting decrease in pressure in the tip (30, 34) is measured to stop its advance towards the surface (37) and then to start dispensing. In circumstances wherein the contacted surface (37) is hydrophobic so as to ideally require a meniscus depth greater than the nominal depth, the tip (30, 34) is retreated from the surface (37) during dispensing to an ideal depth ( DELTA h').