AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |
Back to Blog
If the conveyor is running and the load fails to reach the photoeye within a prescribed period of time (10 seconds), a fault is detected, and the conveyor stops.Īfter correcting the problem, the operator is required to reset the conveyor by clearing the fault through the man-machine interface. ![]() In this example, a single fault condition is implemented. The operator may subsequently restart the conveyor sequence by pressing the “start” button again. After the operator has pushed the “start” button but, before the photoeye is blocked, the operator has the option of pushing the “stop” button, causing the conveyor to halt. When the command is received, the load is transferred off the conveyor, and the conveyor stops once the load has cleared the photoeye. The conveyor then waits for an external command originating from another module. A conveyor system example is explained above. The load is then conveyed to the left end of the conveyor, and the conveyor stops when the photoeye is blocked by the load.įigure 1. The operator places a load at the far right end of the conveyor and pushes the “start” button. The behavior of each module is defined based upon an understanding of the process and specific equipment such as actuators and sensors on the plant floor.Īs a simple example, consider the conveying system depicted in Figure 1 below. The modules are defined naturally by partitioning the control application.Ĭommonly, a module represents the function of a single piece of equipment such as a pump, valve, fan, tank, mixer, blower, etc. A module includes the functional description of the behavior of a self-contained “chunk” of sequential logic. The Development Process Methodology State Module DefinitionĮach distinct segment of sequential control is represented by a module. A nice property of this methodology is that “if then else” rules along with the ability to perform “looping” can be applied to ladder logic. The state description is then manually translated directly into ladder logic. ![]() We examine a simple sequential control example of a basic conveyor and demonstrate the methodology involved in defining the problem in terms of states. The traffic light change may be triggered by a particular flow of traffic that has occurred in the recent past. Representing sequential control via the concept of “state machines” is an established and appropriate technique.Īn example where sequential control might be applicable is in the control of a traffic light. Sequential control produces process outputs that not only depend upon the state of process inputs but also based on the history of the input patterns. Ladder logic is used to control machinery and direct processes in industrial control applications.įrequently, there is a desire to utilize ladder logic for sequential control applications. Ladder logic is a common visual programming language that can execute in a PLC.
0 Comments
Read More
Leave a Reply. |