Patent ID: 7243052
Filing Date: 2007-07-10
Classification: G05B

Abstract:
1. A method of determining hysteresis of a process device in a process, the method comprising measuring a control input to the process device during normal operation of the process device in an industrial process, measuring a process output of the process device during normal operation of the process device in the industrial process, collecting sample pairs of signals representing said control input and said measured process output of the process device during normal operation of the process device in the industrial process, storing the collected sample pairs in a database, calculating the hysteresis of the process device on the basis of the collected sample pairs, each collected sample pair including an average control input and an average output for a predetermined collection period, screening the sample pairs suitable for further processing at least according to the magnitude and direction of the relative change of the average control input of each sample pair, grouping the sample pairs into a first and a second group at least according to the direction of the relative change of the average control input of each sample pair, calculating a first and a second control/output characteristic curve by means of the screened sample pairs of the first and the second group, respectively, determining and storing the hysteresis of the process device as a distance between the first and the second characteristic curve at least at one point.