M8251 PLS Module

Principle of Operation
The PLS module uses a resolver coupled to the machine shaft to acquire position information. The module  constantly reads & decodes resolver signals, and then turns up to 16 PLS outputs on and off, based on user  programmed set-points. The whole operation is much faster and is independent of the PLC.

Module  setup
The M8251 gives you many choices to setup the module. You may setup the module from the keypad, PLC,  or a PC. When programming from the PLC, you write a ladder logic program to set up parameters in the  module. The manual contains programming instructions for the user that enable him to enter the values/data  which are auto-matically read and written as ladder logic rungs. The M8251 PLS module interfaces with the  Modicon PLC using Input & Output registers.

Programmable Resolution & Zero Offset
The PLS module has programmable resolution from 17 to 1,000 counts per turn. The  unit features a dynamic zero-ing or Mod-Z (Modification Zero) to modify the zero  reference point, inde-pendent of the actual resolver position. After the PLS receives the  Mod-Z input, the resolver position is reset to zero.

Brake Monitor
The unit offers time- based Brake Wear Monitoring to satisfy the OSHA require-ment. The unit displays Press  Stop Time after each stop of the machine. The unit can be programmed to have Brake  Wear Monitoring Functionality (initiated by entering a Caution and Danger limit). These  outputs are activated if the stop time exceeds the programmed limits. If you do not select  Brake Wear Monitoring, the user must select ModZ or the unit defaults to normal PLS  func-tionality.(If Brake Wear is selected, the unit cannot function as Mod-Z.)

Motion  Detection
The unit has a built-in tachometer and motion detector. The motion detector can only energize a relay when the RPM is between the programmed low and high  alarm values.

Advanced Features
The unit features a Speed Compensation (Rate Offset)  to compensate for speed variations. The Rate Offset, individually programmable for each  channel, is used to advance the PLS settings as a function of the machine speed. In  addition, it has 4 channels that have Multislope Speed Compensation, programmable in 16 zones.

Angle ON-Time OFF
The unit can be programmed to have its outputs turned ON at an angle and turned OFF  after a programmed time (instead of angle). For example, Channel 12 can be turned ON  at an angle of 100° and stay ON for a period of 2.45 seconds. This feature is useful for controlling air or lubrication.