Abstract: A magnetic flow meter includes a cylindrical vessel within which electrodes are placed directly opposite each other about a magnetically permeable core. In that way, two flow channels are obtained in the vessel. A common magnetic field is applied across both flow channels. The magnetic flow meter is used in conjunction with a controller which monitors amplitude modulated signals representative of applied magnetic field and induced electric field. These amplitude modulated signals are passed to Sigma-Delta modulators, which directly digitise the amplitude modulated AC signals into digital pulses. The controller is capable of monitoring reverse flow through the meter, and to store results until forward flow resumes. Moreover, the controller generates a driving signal for coils which generates a magnetic field, the coil being placed in conjunction with a capacitor which causes resonance. This reduces power consumption by the coil in driving the meter.

Abstract: An etching system (1) comprises a host PC (20) which stores a bitmap etching pattern (210) and transmits this via its own interface (200) and a data link (30) to an etching apparatus (10). The etching apparatus (10) includes its own interface (170) which receives the bitmap etching pattern (210) and passes it onto a control unit (110). The control unit (110) generates control signals for an etching head driver (120) which in turn drives an etching head (130) to eject etchant from an etching reservoir onto an item to be etched. The etching head (130) is moved relative to the item to he etched by means of motors (151, 152) which are driven by motor drivers (141, 142) which are also controlled by the control unit (110). The etching head (130) selectively deposits droplets of etchant onto the item to be etched in such a way that unwanted portions are removed by the droplets of etchant whilst wanted portions are maintained intact.