Ratio bias, Ratio bias control, Ratio bias controller – Micromod MOD: Modcell 2050R Users Guide User Manual

Page 189

IB-23C650

RATIO BIAS CONTROL

RATIO BIAS CONTROLLER

Ratio bias control systems maintain two or more process variables at a
predetermined relationship, or ratio. In a ratio bias controller the ratio or bias
value is applied to the remote set-point input before the set-point is passed to
the PID algorithm. The output of the PID algorithm controls the dependent
flow valve in order to maintain the correct ingredient relationship. Ratio and
bias values are entered locally through the instrument operators display. If
ratio or bias values are to be entered from a remote source, see A/M Ratio
Bias Station.

In figure 20, the instrument is acting as a single station ratio or bias controller
where two flow streams are blended. This application requires that an option
card be installed to bring in the remote set-point signal (independent flow).

Figure 20. Ratio Control of Flow (Two-Stream Blending System)

Process Input

Remote Set-Point

Dependent (Controlled) Flow

Independent (Wild) Flow

S-3007-247

Ratio

Controller

Flow

Transmitter

Flow

Transmitter

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