Chemtrac HydroAct HA4, Руководство пользователя

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4.1 PID Control 65
4.1.1.1.3 Derivative Term
The derivative term is calculated by determining the slope of the error over time and multiplying this
rate of change by the derivative gain, adjustable in the PID configuration.
D
out
= K
d
[
e
−
p
δ t
]
where D
out
is the derivative term output, K
d
is the derivative gain, δ t is the loop time, e is the error and
p is the previous error.
The derivative term slows the rate of change of the process variable. Derivative control is used to
reduce the magnitude of the overshoot produced by the integral component and improve the process
stability. However, the derivative term is susceptible to noise in the process variable signal and can
result in an unstable system if the noise is too high.
4.1.2 Operation
When selecting the PID control tile from the main menu of the HydroAct 4, the control overview tile will
be displayed.
The overview display of the PID controller is designed to allow the user to see the output and
key information, and also be able to see key actions without having to enter the setup of the PID.
Information shown includes the process variable, the target setpoint, the controller output and its
operational mode. Options available for user input are:
Run Mode Options include: “Off”, “Manual”, “Automatic”.
Manual Value
Sets the output when in manual mode. Options are between 0.00%..100.00%.
Setpoint
Edit the setpoint within the range of the process variable.
Also on the display is a “Boost” button, if it is enabled. This engages the “Boost” function. See
section 4.1.2.6 for details. If the control is in fail mode due to an error, the “Reset” button will be
available to restart the control.
The following sections describe the functionality found in the pop-up menu that appears when
pressing “Options”.
4.1.2.1 Control Setup
This control is configured via the user interface of the HydroAct 4. To access the configuration, log in
with advanced privileges and select:
Options
→
Setup
→
Control Setup