The WD family of controllers allows for standalone monitoring of signals from the MS family of speed switches. Of course, a plc would be more economical for applications that require many speed switches. The WD1 Watchdog Relay can be used with one MS speed switch. The WD2 Watchdog Relay can monitor up to 8 MS speed switches. Both models provide 8 amp contacts that can be used for anything from warning horns to interlocking. Both models provide din rail mounting. Drop out time on the WD1 is adjusted by an external knob and the WD2 is a programmed setting which can be factory set or changed in the field.