High Reliability Drop‐Fall Detector for Computerized Drop‐Time Measurements

Abstract

An electronic drop-fall detector for dropping mercury electrodes is described. The device has been conceived to work in a computer controlled apparatus. It offers an accuracy better than 500/Lsec and a false triggering rate better than one error over 104 drops.A fully computer controlled apparatus for electrocapillary measurements by the drop-time method has been assembled in our laboratory. It has been conceived to work continuously for several days unattended; thus, a drop-fall detector was needed with:(i) high accuracy, (ii) high noise immunity, and (iii) no need of trimming along a full run, even with solutions of different conductivity. A brief review of the available techniques, with a comparative analysis, can be found in Ref. (1-3).We agree with Tyma (1) in considering the technique based upon a-c impedance measurements as being at present the most suitable one. Lawrence and Mohilner (4) have proved the absence of any perturbation due to the a-c signal on the interface, and various circuits have been described (1, 3, 5).However, features (ii) (i.e., the insensitivity to statics and to the electromagnetic disturbances generated by the other laboratory apparatus) and (iii) (i.e., the ability to work properly for a long time without loss of performances even when solutions of very different conductivity are used) are hardly at-* Electrochemical Society Active Member.