Emec LDSPH PLUS Series, Руководство по эксплуатации, Страница: 13 / 44

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8.5 “PID”, pH
A proportional-integral-derivative controller (PID controller) is a control loop feedback mechanism (controller) widely
used in industrial control systems. A PID controller calculates an error value as the difference between a measured
process variable and a desired setpoint. The controller attempts to minimize the error by adjusting the process
through use of a manipulated variable. The PID controller algorithm involves three separate constant parameters,
and is accordingly sometimes called three-term control: the proportional, the integral and derivative values, denoted
P, I, and D. Simply put, these values can be interpreted in terms of time: P depends on the present error, I on the
accumulation of past errors, and D is a prediction of future errors, based on current rate of change.[1] The weighted
sum of these three actions is used to adjust the process via a control element such as the position of a control valve,
a damper, or the power supplied to a heating element.
To correctly setup PID as working mode configure the following parameters within two menus “SETPOINT MODE
PID” and “PID PARAMETERS”
1) Choose related output to work into PID mode using Setpoint menu
2) Enter RANGE value. Range is the maximum PID value over or under which (depending on pH+ or pH-) the
instrument will automatically switch into proportional mode
3) Enter SETPOINT which is the optimal value to achieve. Move the cursor to OK and save the data.
4) Select “PID PARAMETERS” within SETPOINT submenu
- Choose working mode (+ or -) baed on how setpoint must be reached: starting from lower or higher values.
- Enter INTEGRATIVE value (time needed to the instrument to activate a procedure as answer to a plant’s change. E.G.: time
needed for pump activation when reached a set value. ) Default value: 60 seconds.
- Enter DERIVATIVE value ( time needed to the instrument to react to a plant’s status change. E.G.: if pH value in water
increase, the time integrative is the time needed to notify the change.) Default value: 3 seconds.
- Move curson on OK then click to save settings.