Hach EC1000, Инструкция по эксплуатации

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4.3.1 Reset (Integral)
Please see Figure 8 for a diagram of the controller output response (integral only) to a step
change on the input. The integral action is used to drive the loop so that there is zero long
term error. For example, on a proportional controller where the steady state pH is too high,
the integral component of the output starts ramping up until the increased chemical feed
brings the pH down to the set point. The higher the setting, the faster the loop reaches
steady state, but it should not be set faster than the delay times in the loop. If the setting is
too high, the loop goes into oscillation (this generally tends to be a slower oscillation than
that caused by a gain or derivative setting that is too high). The integral action is turned off
by setting it to zero.
4.3.2 Rate (Derivative)
Please see Figure 8 for a diagram of the controller output response (derivative only) to a
step change on the input. The derivative action reacts to rate of change of the input and
attempts to counter fast changes. The derivative action is turned off by setting it to zero.
4.3.3 Curve
The curve mode entry has three settings (, linear-, curve). For most applications
either or linear- is used. is selected when the control pump is set up so that
an increasing controller output signal causes the pH to increase. Linear- is selected when
the control pump is set up so that an increasing controller output signal causes the pH to
decrease.
The use of the curve selection can improve the control loop if the characteristics of the
sample are repeatable over time. For optimal control, the loop gain (controller gain
x
process gain) should remain constant, but for most samples the process gain changes over
the pH range.
Please see Figure 10. The process gain (defined as:
∆
pH /
∆
% reagent addition) at point 1
through point 5 is represented by the slope of the line between each point and the setpoint.
For this example, the slope of the line (process gain) changes considerably depending on
the pH of the sample. If this curve is entered into the EC1000, the controller can
compensate for the change in process gain to keep the loop gain constant.
To implement the titration curve, take a sample of the process water, and titrate with the
reagent (acid and/or base used in the process). Record the pH value (Figure 11). Enter this
curve into the instrument as percent reagent addition vs. pH. The final step, after entering the
titration points, is to go back to the curve mode entry, and select the curve setting.