Analog Signal Derivation in the Programmable Logical Controller

Abstract

Programmable logical controllers (PLC) find ever-widening applications in technological processes of ground operating equipment. Their computing capacity allows additional processing of analogue signals coming from the sensors of physical quantities. In particular, PLC hardware and software enable us to calculate the first derivative of an analogue signal in order to improve the control or prediction quality of the process under control. The aim is to research the singularities in calculating the first derivative of an analogue signal using the SIMATIC S7-200 PLC of Siemens Company. A method of digital differentiation has been decided on the algorithm based on a derivative representation by a final number of return differences of consecutive readout in regular intervals of continuous function. Such an algorithm allows us to find comprehensible accuracy in calculation of the first derivative of an analogue signal in PLC when using the first and second differences of readout. Thus, a choice of the period of digitization of differentiated process is also of great importance. Research of the differentiation process, based on mathematical models of aperiodic chains of the first and second orders, has shown that for used PLC a digitization period should not be less than 50msес. The natural experiment has shown that calculation of the first derivative of a signal from the temperature sensor allows an essential increase in speed of PLC response to the abrupt change of the measured quantity. The research results have shown that SIMATIC S7-200 PLC allow us to provide sufficient accuracy and speed in calculating the first derivative of the low-frequency analogue signals, being specific, for example, for re-fuelling systems or systems of temperature stabilization. The received results are of interest for experts in the field of development and operation of technological systems of the ground operating equipment.