Abstract: The invention is concerned with an injection mold for making a plastic impedance measurement module having a generally flat metal grid imbedded in the plastic thereof with a plurality of pairs of electrodes upstanding generally perpendicularly from said grid, one pair into each of a plurality of chambers, said electrodes being uncoated by said plastic.The process comprises placing the grid adjacent a first mold half of an injection mold with the electrodes each within a respective one of a plurality of slots extending into the first mold half, the first mold half having a first generally flat recessed portion defining a top surface of a base of the module and a plurality of channels extending from the first portion into the first mold half defining the plurality of chambers.

Abstract: Digital apparatus is disclosed which provides means for plotting the change with respect to time in the impedance ratio between a pair of cells, both cells of the cell pair containing a selected nutrient media and one (specimen) cell of the cell pair further including a micro-organism contaminant the growth of which is to be detected. Growth of the contaminant within the specimen cell over a selected period of time provides a characteristic change in the impedance of the specimen cell which provides, in turn, a corresponding change in the impedance ratio between the cells of the cell pair. Measurements are digitally made via means which compares the impedance ratio between the cells of the cell pair to successive resistive approximations of the ratio, and then outputs a digital word corresponding to the nearest approximation. Each digital word thus represents the impedance ratio at a given point in time of growth.