PURPOSE: To enhance the reliability of a data to be collected by preventing update of a data file so that an incorrect data is not inputted when a capacitance strip is cleaned or replaced.

CONSTITUTION: A bottle 70 is advanced along a supporting plate 12 by means of a carrier 14. The carrier 14 applies a force to a capacitance strip 16. A bracket 20 is connected with a corresponding oscillator 24 through a post 22. The oscillator 24 receives a capacitance signal through a line 26 and generates a voltage signal to a computer. When the strip 16 is cleaned or replaced, an operator switches the system to a cleaning mode, i.e., turns a switch 50 off. When the system is in that mode, all data being generated is neglected and the data file is not modified. When the switch 50 is opened, all channels being used before cleaning are available and a data file is updated.