PNNL

Abstract

Control software for an automated particulate air sampler is described. The software is divided into a number of small, cooperating server processes, each of which is responsible for the control of a particular device or subsystem. For each process, an effort was made to isolate the details of the underlying device or subsystem from the server interface. This made it possible to change the hardware without making changes to any of the server's client processes. A single supervisor process is responsible for overall system control. The design of the control algorithm was facilitated by employing a state machine model. Such a model is easy to study, easy to modify, and provides a clear understanding of the control mechanism to programmers and non-programmers alike. A state machine library was developed which greatly eased the task of implementing the design and ensured that the control algorithm detailed by the state machine model was the same algorithm that was actually employed.