Most people are aware that Functional Devices, Inc. sells current switches. We offer a few variations, like solid core vs. split core, fixed vs. adjustable threshold, and wires vs. terminals. However, there are two of our current switches that I doubt as many people know about. The Self-Calibrating Current Switches.
Self-Calibrating Current Switches
Self-Calibrating Current Switches are unique among our offerings and are available in two models, RIBXGA-SCAL (wires for field connection) and RIBXGTA-SCAL (terminal for field connection). Most of our current switches have a normally open output that closes when current through the core exceeds the threshold. However, the output of the self-calibrating version (-SCAL) is only closed when the current sensed is within a selectable range above and below the threshold. The -SCAL unit calibrates itself and sets the threshold to the nominal current of the load.
To set the threshold, the current switch is clamped around one of the conductors to the load. When current flows through the conductor for the first time, the -SCAL unit begins its calibration process. This lasts for 30 seconds. After that time, the threshold is set at that nominal current. A DIP switch on the unit allows for re-calibration at any time. A second DIP switch is used to set the threshold differential. The differential is the percentage of current above and below the nominal current that defines the range where the current switch is closed. This range can be set to ±15% or ±25%. For example: If the nominal current of the load is 100 Amps, and the differential is set to ±25%, the output of the current switch would be closed from 75 – 125 Amps.
Benefits of Self-Calibrating Current Switches
Having a current switch that is only closed within a range of the nominal current is beneficial in many applications. It can be used to help protect expensive mechanical equipment. The main application is to sense current to a motor, where a current below the range could indicate a belt loss scenario, and a current above the range could indicate a locked rotor scenario. Both states could be detrimental to the equipment. The addition of the -SCAL unit could alert maintenance of such a situation or be used to shut the equipment down completely.