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User Solutions continued
Chapel Hill decided to work with Affinity Energy (www.affinityenergy.com) after hearing of the company's reputation for open-system PLC integration for critical systems.
Specifying a New Control System
Several types of hardware were being used to control the chambers. Each performed essentially the same functions, but there were changes in newer iterations of cooling technologies. Affinity Energy designed a customizable, universal panel prototype to regulate temperature in all of UNC Chapel Hill's chambers, regardless of the existing controller or cooling technology.
There are three types of heating or cooling systems in the chambers, distinguished primarily by solenoid valves controlling liquid or hot gas, or by proportional valves controlling liquid, hot gas or reheat. Solenoid valves operate differently from proportional valves, so different control methods are used, as well as different program logic. This is typically addressed by using a controller specific to the type of valves, so a controller for solenoid valves could not be used on a chamber with proportional valves.
A primary goal of the project was to find a programmable logic controller (PLC) that could be used in any of the chambers, regardless of the devices being controlled. This first controller was considered a prototype
since it would have to be used in many different cham- bers.
After extensive hardware and controller research, UNC Chapel Hill and Affinity Energy specified AutomationDirect PLCs. Because AutomationDirect's PLC programming software is open, the university wouldn't have to be held hostage to proprietary soft- ware or a single system integrator's services if they wanted to adjust or completely overhaul the system in the future.
Using the New Control System
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Open System Provides Precise Temperature Control
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Figure 3: (courtesy of Af nity Energy) Af nity Energy replaced the obsolete controller with an AutomationDirect PLC and HMI due to the open, precise control capabilities and ease of use of these components.
Previously, researchers had only rudimentary indica- tion of a room's temperature, and in case of failure, there was no indication until opening a cold room door and feeling a warm blast of air. The old controller also had significant fluctuation between set point thresholds. Affinity Energy designed a temperature control system using AutomationDirect's Do-more PLC (Figure 3).
The new controller provides smoother and more accurate control than the legacy control systems. The controller enclosure is built with the PLC and other control devices (drivers, relays, etc.) as a unit. Field devices are wired to terminal blocks included for connections, and the panel is mounted on a wall out-
side the environmental chamber.
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