Testing Procedure for IEC 61131-3 Control Software

Control software often performs complex tasks in industry. Its proper operation is crucial for safety as well as efficient management of system resources and processes. However, testing of such a kind of software is usually less organized than in traditional business IT applications. In this paper, procedures and tools for control software testing are proposed. The modeling stage of project development involves SysML as a specification language for Program Organization Units and POU-oriented tests. Corresponding implementation is created in the languages defined in the IEC 61131-3 standard and can be verified using two testing methods, namely table and unit tests. The first option is an easy way of checking whether a function block, a function, or a program produces correct values of outputs for particular values of inputs. More advanced unit tests are specified in a dedicated test definition language, called CPTest+. The proposed procedure is described using the Pulse-Width-Modulator (PWM) example, which is common in the on-off PID control. The presented test tools have been introduced into the CPDev programming environment.