7.40.8 Control valve specification data for application pH setpoint in the steep portion of the titration curve.
(Amax)(Fimax) combination that yields the largest product (increased by 25% to improve the valve gain uniformity) is used to set the maximum capacity for sizing the control valve. The maximum rangeability of reagent flow (Rrmax) is obtained by dividing the maximum product pair by the minimum product pair. The precision of the control valve in terms of its repeatability and dead band requirements is proportional to the ratio of the minimum B value to the maximum A value. The 80% value in Equation 7.40.3 corresponds to the 25% extra capacity used for sizing. For steep curves, B may be too small to estimate unless the titration curve is expanded in the control region (Figure 7.40.8).
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