Procedure and device to create a process-dependent comparison criterion instead of comparing a signal level with a specific absolute level

摘要

The method is for obtaining a process-dependent comparison criterion for use in conjunction with control as to whether a monitored entity value exceeds the process-determined permitted value, and where the entity is represented by sampled measurement values (I(k)). The entity which the sampled measurement values represent is high pass-filtered so that a high pass-filtered representation (Ihp(k)) of the entity is obtained, which is fed to a first selector whose output (Istab(k)) consists of the largest of Ihk(k) and (I-C1)-Istab(k-1). After this, C2-Istab(k) is fed together with Ihp(k) to a second selector and if Ihp(k) is greater than C2-Istab(k) this is interpreted as if the monitored entity exceeds the process-determined permitted values and where Istab(k-1) comprises a sample value a sample before Istab(k) and where C1 and C2 consist of previously selected constants.