lib/pid_st.txt
author mjsousa
Thu, 29 May 2014 12:06:22 +0100
changeset 895 f824bf8e1579
parent 276 1679f514f38a
permissions -rwxr-xr-x
Add error message for invalid datatype of transition condition. Generalize datatype narrowing algorithm for transition conditions.
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(* Following taken directly from the IEC 61131.3 draft standard *)
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(*
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 * An IEC 61131-3 IL and ST compiler.
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 *
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 * Based on the
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 * FINAL DRAFT - IEC 61131-3, 2nd Ed. (2001-12-10)
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 *
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 *)
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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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