Watlow PPC-2000 - Manual (Page 114)

Chapter 3: Operating with AnaWin 3 PPC-2000 User’s Guide
90 Watlow Anafaze Doc.# 30002-00 Rev 2.3
Feedback
Electrical signals from a sensor used to determine a control
output is feedback. The Input parameters determine how the
electrical signal is interpreted. Many standard sensor types are
pre-programmed into the PPC-2000 and can be selected during
setup. The controller interprets or scales the electronic signals
for these sensor types in engineering units (°F or °C). Other
sensor types may require user-supplied scaling information.
See Setting up User Selectable Linear Inputs on page 98.
In some cases the feedback signal may come from a value other
than a sensor input. Using a Soft Input, a logic program can
determine the feedback to a channel.
Control Algorithm
The PPC-2000 determines the appropriate output signal when
a set point is supplied and the controller is set to automatically
control a loop. The controller calculates the output based on the
feedback and the control algorithm. Each channel may use
either On/Off or any combination of Proportional, Integral and
Derivative (PID) control modes. See Control Algorithms on
page 220 for information on these control modes.
The PPC-2000 also includes a manual reset term that may be
used in conjunction with some of the PID modes. See Channels
on page 115 for more information on these parameters.
Control Output Signal Forms
The output level calculated by the controller is represented by
a percent (0-100%) of power to be applied. That value is applied
on a digital or analog output according to the user-selected
output type. See Output Control Forms on page 224 for more
information on the output types available.
Heat and Cool Outputs
The 48 control channels may each have one or two outputs.
Often a heater is controlled according to the feedback from a
thermocouple and, in that case, only one output is needed.
In other applications, it is possible that two outputs may be
used for control according to one input. If, for example, a
system with a heater and proportional valve that controls
cooling water flow are controlled according feedback from one
thermocouple, the channel has one input and two outputs.
In such systems, provisions are made in the control algorithm
to avoid switching too frequently back and forth between the
heat and cool outputs. The On/Off algorithm uses the Spread
parameter to prevent this bucking. See Channels on page 115
for more information. When PID control is used for one or both
channel outputs, both the spread and the PID parameters
determine when control switches between heating and cooling.