Low-Pass Filter

[Suseh 0]

Good Morning, i have a variable [REAL] - for example i will name it "PV" which occasionaly has a sudden changes. This variable - PV - is going to PID controller. I do not want that this "shots" of value were places in my PID loop. So i want to use LPS. For now i try to use LPS block but without success. I read a lot of LPS (there is many theoretical information about it but unfortunateley not enough connected with PLC). The most popular which i find: FV=FV(n-1)+C*(NV(n)-FV(n-1)) FV - filtered variable C - constant, range: <0,1> How can i implement FV(n-1) - previously sample? Many thanks for advice, Suseh

[Suseh 0]

Good Morning, i have a variable [REAL] - for example i will name it "PV" which occasionaly has a sudden changes. This variable - PV - is going to PID controller. I do not want that this "shots" of value were places in my PID loop. So i want to use LPS. For now i try to use LPS block but without success. I read a lot of LPS (there is many theoretical information about it but unfortunateley not enough connected with PLC). The most popular which i find: FV=FV(n-1)+C*(NV(n)-FV(n-1)) FV - filtered variable C - constant, range: <0,1> How can i implement FV(n-1) - previously sample? I use ControlLogix. Many thanks for advice, Suseh

[Mickey 71]

The same but different. FV=FV+C(NV-FV) Where: FV= Filtered value C= constant (range 0-1) The smaller the number the more dampening. NV= New Value

[Suseh 0]

Hi, something like that - see atachement, please.

[b_carlton 61]

Just before performing the calculation store the current FV. The stored value is used as FV(n-1) while FV will be replaced as a result of the calculation.

[Suseh 0]

My previoust way does not work. When i very the project i saw that we can not connect output into the other block inputs. I do not fully understand how to save previously sample. Normally i make it in that way - see attachement, please. Any suggestions?