I/NET Direct Digital Control (DDC) Modules

[Product_Support]

Issue

A more in-depth description of each of the Direct Digital Control (DDC) modules in I/NET

Product Line

TAC INET

Environment

• I/NET DDC
• DCUs, PCUs, MRs
• Two Position Module (2POS)
• PID Controller (PID)
• Float Module (FLT)
• Reset Module
• DDC Hi/Lo Module (HI/LO)
• Relay Module (Single Pole Double Throw Relay)
• Calc Module

Cause

DDC is a system that measures a variable, compares the variable with a known value to determine the error, processes the error using a specific software algorithm, and then produces an output to modify the controlled variable.

Resolution

Most of these modules are discussed in both TCON 083 or  TCON 299 System Operator Guide for more details. (The System Operator Guide is installed by default on your I/NET Host Workstation)

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DDC Two Position Module (2POS)

This module is used where the final control element is in either one state or another opposite state (ON/OFF, OPEN/SHUT). This type of control will commonly be used for simple heating or cooling systems, starting and stopping motors, controlling water sprays for humidification, etc. This module is available in our PCUs and DCUs; and you can customize it for your needs. 

DDC PID Controller (PID)

In Proportional (P), Proportional + Integral (PI), and Proportional + Integral + Derivative (PID) control, the control element moves linearly to a position that is proportional to the deviation and the rate of deviation of the controlled process variable from a prescribed setpoint. This type of control, in any of its three modes, or combinations thereof, is commonly used for the control of modulating valves, vanes or modulating motors where a proportional output control point is used. The proportional output control point may be either an analog output (voltage, current, resistance) or a pulse width output where the duration of the pulse is proportional to the error variation. This module is available in our PCUs and DCUs; and you can customize it for your needs. 

DDC Float Module (FLT)

Traditionally, floating control actuates a control device when the error, i.e. the difference between the controlled process variable and the setpoint, exceeds a deadband and maintains the control until the error is within the deadband. The floating controller is based on the same principle however it has been enhanced to include PID control without the requirement for analog output or pulse width position feedback. The output of this controller may be directed toward either a pair of variable pulse width discrete outputs to control a bi-directional drive motor or dual EP value arrangement which is generally described as a "pressure-vent" controller. This type of control is commonly used for the same applications as the PID controller where positive feedback is either unnecessary or economically unsound. This module is available in our PCUs and DCUs; and you can customize it for your needs. 

DDC Reset Module (RESET)

Reset is used to develop a setpoint output in an inversely or directly proportional relationship to one or two analog inputs and one or two operator-specific reset schedules. This module is available in our PCUs and DCUs; and you can customize it for your needs. 

DDC Hi/Lo Module (HI/LO)

This module is used to provide the highest and/or lowest value from two or more measured variables, most commonly temperatures. HI/LO can be cascaded to accommodate virtually any number of inputs of similar nature. Typically the lowest space temperature would be the most logical to use to directly reset the heating water setpoint. The HI/LO modules provide the control engineer with a convenient alternative method for making the selection. The HI/LO modules may also be used as an OR/NOR selector by using the state(s) of various monitored discrete points. This module is available in our PCUs and DCUs; and you can customize it for your needs. 

DDC Relay Module (Single Pole Double Throw Relay)

This module provides a mechanism for selecting one of two values or states based on conditions within the controlled environment. The actions of the relay are controlled by one discrete input and control which of two input states or values is directed to the output. The inputs and output may be either discrete or analog. The actions of this relay are analogous to its electric/electronic counterpart in its simplest form. This module is available in our PCUs and DCUs; and you can customize it for your needs. 

DDC Calc Module

This module functions similarly to calculations added to a point through the calculation extension editor. This module is only available in Micro Regulators (MR). It is not available in Application Specific Controllers (ASC).