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...2 OPERATOR LEVEL
2.9 Ratio Controller (Templates 14 and 15)
Ratio control enables a controlled process variable to be maintained automatically in definite
proportion to another variable known as the wild variable. The wild variable, weighted by ratio (rAtO)
and bias (bIAS), values forms the control set point for the process variable.
Local Ratio
•1
Remote Ratio
I/P3
Wild Variable
I/P2
Process Variable input
I/P1
•1 Template 15 only
Control
Set Point
Process
Variable
(PV)
OP1
Control
Set Point
Process
Variable
(PV)
OP1
•1 Only displayed if enabled in Level B, Operator Configuration – see Section 4.7.
26
L
L R
rAtO
WV x rAtO + bIAS
WV
Fig. 2.8 Ratio Controller
55. 0
50. 0
70
•1
bIAS
0. 0
70
Manual Output
CSPt
PID
PV
Control Loop
Actual Ratio
Process Variable (PV) – Bias
=
Wild Variable (WV)
Desired Ratio
Adjustable in Local control only.
Control Set Point = (WV x Ratio) + Bias
Control Output
[0 to 100% (–10 to 110% for analog outputs)]
Adjustable in manual mode only.
Bias
[in engineering units]
Return to
Actual Ratio
Control
Output
OP1
PID O/P
display.
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