CRITICAL PNEUMATIC COMPONENTS IN THE PROCESS CONTROL INSTRUMENTATION

The pneumatic instrumentation still covers an important application field in the control of chemical processes and similar ones. In this type of instrumentation the transmission line still remains the main critical component. The investigation of the line length limits is necessary to establish the acceptability of the pneumatic instrumentation. The dynamic behaviour of the line and the closed-loop is separately investigated, while the benefits obtainable from the introduction of one derivative relay are outlined on the basis of experimental results. The tests are carried out on closed control loop simulator using industrial actual components and real line. The results give some contribution for better evaluation of the limits of pneumatic instrumentation and the advantages produced by the use of a derivative compensating relay. Additional consideration look for the possible improvements in computation and control function and for the decrease in reliability due to various factors.