Abstract: There is provided a detector for detecting conductive contaminants entrained in an airflow. The detector comprises first and second electrically conductive meshes mounted in a spaced apart relationship to provide an operational gap. Each of the meshes is sized to provide a relatively large surface for substantially intersecting the airflow and is sufficiently porous so as not to substantially attenuate the airflow. The meshes form part of an energizable electric circuit wherein the operational gap constitutes a discontinuity of the circuit. The detector includes a capacitor connected in parallel to the portion of the circuit containing the operational gap for releasing a charge stored in the capacitor through the circuit discontinuity when one of the conductive contaminants simultaneously contacts the first and second meshes. The detector further provides for indication of a discharge of the capacitor and thereby the presence of one of the airborne conductive contaminants entrained in the airflow.

Abstract: The approach to measuring load current in a multi-phase bridge inverter circuit connected to a multiphase load involves placing a single current sense resistor in series with the inverter circuit and power supply. The current flow through the sense resistor is sampled during a portion of the switching cycle wherein the inverter is configured to enable current flowing through the multi-phase load to flow through the sense resistor. Typically, this will occur during a portion of the switching cycle (e.g. PWM cycle) wherein the load is being actively driven. For a 120.degree., 3-phase, 6-step commutation sequence typically used to control a d.c. brushless servo motor, the sampled current is a time-multiplexed measure of the current flow through each load phase. The same sense resistor is also used for indicating a short circuit condition by comparing the voltage across the resistor to a reference voltage.