The Series 1991 PLS is an ultra high-speed programmable limit switch designed to provide set point control in high-speed machine applications. Its hardware driven logic circuits operate at a throughput time of 10 microseconds (.00001 seconds) on the first 16 output circuits. This allows one count accuracy on systems with 3600 counts per revolution scale factor at speeds over 1600 RPM. Speed compensation software allows independent rates of advance or retard on the leading and trailing edge of a programmed set point. This allows full compensation for both the on and off response time of the machine function being manipulated for precise control of its location and duration within the machine cycle. Operation programming can be done through its keypad or remotely via RS232 or RS485 from a PLC, PC or any computer device with two-way serial communications capability.