It is conventional, in providing aspirators in an analyzer, to sense the position of the aspirator to prevent vertical overtravel. For example, analyzers provided by Eastman Kodak Company under the trademark "Ektachem 700" have a sensor to determine when the aspirator has lowered a sufficient distance to pick up, by force-fit, a disposable tip. Such sensors are vertically adjusted so that, as part of the set-up calibration, the operator can adjust the trigger location of the sensor depending on that particular analyzer's margins of error. Other instruments have similarly adjusted sensors. See, for example, U.S. Pat. No. 4,705,667 (Column 6, lines 37-44). Once adjusted, the sensor then cooperates with a single flag for each movable part, since that flag is sufficient to trigger that the limiting condition is achieved.
One difficulty of such a construction is that when replacement parts are incorporated into the analyzer proboscis, the set-up calibration (including the positioning of the sensor) has to be recalibrated, which has to be done manually. This is time-consuming and expensive.
Therefore, prior to this invention, there has been a need to provide a proboscis with a sensor for set-up calibration that allows recalibration without readjusting the sensor. This has not been possible with the conventional configuration described above.
Yet another drawback of the previous construction has been that, with only a single flag acting with the sensor, the proboscis can detect only that it has been interrupted. It is unable to determine the nature of the interfering objects since, although the proboscis may be stalled, the flag is not in position to interact with the sensor.