Elster Instromet 2000 - Page 53

Model 2000 Flow Computer Instruction Manual
2.0 GENERAL DESCRIPTION
Model 2000 issue 21 Page No
46
Epsilon, if “SP Control” is “As PV Control”
eSPPV
eSPPV
ee e
P
I
DPn Pn
=−
=−
=−
−
∆
,,1
Epsilon, if “SP Control” is “Only I -action”:
n1nD
initialP
I
PVPVe
PVSPe
PVSPe
−=
−=
−=
−
∆
When the PID controller is used in reverse mode:
ee
ee
ee
PP
II
DD
=−
=−
=−∆∆
PID actions:
actionactionactioncalc
D
dgainaction
i
gainI1nactionncalc,action
gainPaction
DIPOut
t
e
TPD
T
t
Pe)I()I(
PeP
++=
××=
××+=
×=
−
∆
∆
∆
Where
Pgain : Proportional gain
Pband : Proportional band
SP : Set point
SPinitial : Initial set point ( = PV at start-up)
PV : Process value
PV,n : Current Value of PV
PV,n-1 : Previous Value of PV.
eP,n : Current Value of eP
eP,n-1 : Previous Value of eP
eP : Epsilon for Proportional action
eI : Epsilon for Integral action
∆eD : Epsilon for Derivative action
Paction : Proportional action
Iaction,calc : Calculated Integral action
Iaction : Finally used Integral action
Daction : Derivative action
Ti : Integration time
Td : Derivation time
∆t : Last program cycle time
Outcalc : Calculated Output value
When setting up PID Control Outputs the Analogue Outputs (See Analogue Outputs page) will need to be selected from the
Analogue Outputs variable tree and dragged across to the appropriate output as described on the analogue outputs page.