M7251 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 setpoints. The whole operation is much faster, and is independent of the PLC.

Module  setup
The M7251 gives you many choices to setup the module. You may setup the module from the PLC or  a PC. When programming from the PLC, you write ladder logic program to setup parameters in the module.  The manual contains programming instructions for the user that enable him to enter the values/data which  are automatically read and written as ladder logic rungs. The M7251 PLS module interfaces with the PLC  using Input & Output registers.

Dynamic Zeroing
The unit features a dynamic zeroing or  Mod-Z Modification Zero) to modify the zero reference point,  independent 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  requirement. 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 functionality. (If Brake Wear is  selected, the unit cannot function as Mod-Z.)

Built-in Motion Detector and Tachometer
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.

Leading- and Trailing-Edge Speed  Compensation
The unit features a Speed Compensation (Rate Offset) to compensate for speed variations. The Rate Offset, individually program-mable 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.