D8 Series User’s Guide
Chapter 4: Operation and Setup
68
5. To edit a parameter:
– Press
<
or
>
to choose a value.
– Press
.
to save the new value and go to the next parameter.
– Press
x
to cancel a change without saving.
6. Repeat from step 4 to edit another parameter in the current menu.
7. Press
x
to return to the top-level menus.
8. Repeat from step 2 to go to another menu, or press
x
to exit the setup menus.
For information about setting parameters through communications, see Chapter 3: Communicating
by DeviceNet on page 45.
Setting Up Closed-Loop Control
Closed-loop control is used to control an output based on feedback from a sensor or other signal.
Feedback
The controller receives electrical signals, or feedback, from a sensor or other device. The input
parameters determine how the controller interprets the signal. The controller interprets or scales the
input signal in engineering units such as °C or °F.
Control Algorithm
When the controller is in automatic control mode and a set point is supplied, the controller
determines the appropriate output signal.
The controller calculates the output signal based on the feedback and the control algorithm. Each
loop may use either on/off control or any combination of proportional, integral and derivative (PID)
control. Chapter 5: Tuning and Control on page 87 for more information about these control
methods.
Control Output Signal Forms
The output level calculated by the controller is represented by a percentage (0 to 100 percent)
of power to be applied. That value is applied on a digital or analog output according to the user-
selected output type. Heat/Cool Output Type on page 116 for more information about the output
types available.
Heat and Cool Outputs
In some applications, two outputs may be controlled according to one input. For example, a
loop with both heat and cooling water flow might be controlled according to feedback from one
thermocouple.
In such systems, the control algorithm includes provisions to avoid switching too frequently between
the heat and cool outputs. The on/off algorithm uses a hysteresis parameter. The PID algorithms use
both a hysteresis parameter and the PID parameters to determine when control switches between
heating and cooling.
