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lib/pid_st.txt
author Mario de Sousa <msousa@fe.up.pt>
Mon, 04 Apr 2011 15:22:42 +0100
changeset 275 af3d0e3ac65d
parent 192 c6c2a3d487ac
child 276 1679f514f38a
permissions -rwxr-xr-x
Leave standard function names hardcoded, as these are considered keywords even though
they may not be implemented in the library.
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 FUNCTION_BLOCK PID
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   VAR_INPUT
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     AUTO : BOOL ;        (* 0 - manual , 1 - automatic *)
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     PV : REAL ;          (* Process variable *)
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     SP : REAL ;          (* Set point *)
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     X0 : REAL ;          (* Manual output adjustment - *)
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                          (* Typically from transfer station *)
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     KP : REAL ;          (* Proportionality constant *)
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     TR : REAL ;          (* Reset time *)
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     TD : REAL ;          (* Derivative time constant *)
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     CYCLE : TIME ;       (* Sampling period *)
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   END_VAR
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   VAR_OUTPUT XOUT : REAL; END_VAR
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   VAR ERROR : REAL ;        (* PV - SP *)
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       ITERM : INTEGRAL ;    (* FB for integral term  *)
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       DTERM : DERIVATIVE ;  (* FB for derivative term *)
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   END_VAR
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   ERROR := PV - SP ;
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   (*** Adjust ITERM so that XOUT := X0 when AUTO = 0 ***)
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   ITERM (RUN := AUTO, R1 := NOT AUTO, XIN := ERROR,
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          X0 := TR * (X0 - ERROR), CYCLE := CYCLE) ;
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   DTERM (RUN := AUTO, XIN := ERROR, CYCLE := CYCLE) ;
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   XOUT := KP * (ERROR + ITERM.XOUT/TR + DTERM.XOUT*TD) ;
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 END_FUNCTION_BLOCK
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