Badger Magnetics, Inc

Model 250 Rotary Speed Sensor

Model 250 Rotary Speed Sensor

The Badger Magnetics Rotary Speed Sensor system consists of a speed sensor board, a sense head, and a magnetic “mark”. The mark is mounted on a rotating or moving device, such as a pulley or belt, and the sense head is mounted on a stationary section in such a way that the mark periodically passes parallel to the face of the sensor. The sense head is connected to the speed sensor board through a shielded cable. The speed sensor board contains a single relay with two Form-“C” contacts that are available for connection to external alarm or shutdown circuits. This relay is energized during normal operation, and so provides fail-safe operation. If power is disconnected from the board, or if an internal board failure occurs, the relay will de-energize, causing a fault condition. In operation, the speed sensor board measures the period between mark passes and compares it with a preset set point. With the speed sensor board set for Under Speed detection, if the period between mark passes exceeds the set point (the rotating machine is running too slow), the relay on the speed sensor board will de-energize, operating the alarm or shutdown circuit. With the speed sensor board set for Over Speed detection, if the period between mark passes is less than the set point (the rotating machine is running too fast), the relay will deenergize. In addition, in the Over Speed mode, if no mark passes are detected for 5 seconds, the relay will de-energize. This “missing head pulse” detector provides a fail-safe mode in the event that the sense head is damaged, the cable is broken, or the mark becomes damaged or dislodged. If dual speed detection is required, such as a separate alarm and shutdown speed, or a high and low speed limit is needed, a second modified speed sensor may be connected to the same sense head. If a meter indication of actual speed is required, Badger Magnetics can supply a separate tachometer board that may also be connected to the same sense head. Consult the factory for information.