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The Do-more PLC is fast, has plenty of memory, and includes multiple communication options such as serial, USB and embedded Ethernet. It can be configured for several separate Ethernet communications ports, each running multiple protocols. The Do-more PLCs are programmed with the Do-more Designer software, available free online.
Affinity Energy also installed an AutomationDirect C-more human machine interface (HMI). This color touchscreen monitor displays data points such as temperature, humidity, defrost cycle activity, and liquid line
Figure 4: (courtesy of Af nity Energy) The AutomationDirect C-more HMI's main status screen provides temperature and humidity indica- tion,alongwith elddevicestatus.
and hot gas valve status. The HMI is installed in the door of the custom-built enclosure, and is located outside and beside the chamber entrance door.
The main HMI screen displays the temperature in the room and alarm indicator (Figure 4). It also includes status indicators for the various field devices such as liquid and hot gas valves and evaporator fans, and shows whether a defrost cycle is active or not. An operator adjusts the room temperature using the HMI by entering a password-protected screen.
"Not only is the HMI designed for us by Affinity Energy a lot easier to navigate, having the capability to
plug into the controller to conduct maintenance and troubleshooting is a real home run for our techs,” says Mark Obenshain, Assistant Director of HVAC
Operations for UNC Chapel Hill.
To alert researchers and maintenance personnel of out-of-tolerance temperature values, Affinity Energy included alarming functionality. In addition to an alarm
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message displayed on the HMI, an audible alarm mounted on the control enclosure sounds as soon as a temperature rises or falls outside a specific set of parameters.
Not only does the HMI make it much easier to operate the environmental chamber, it also provides data logging to a built-in SD memory card. It can also send an e-mail, access an FTP server, act as a web server and provide remote Internet access. All of these functions are easy to add at a researcher's request.
Due to the nature of research conducted in the chambers, a chart recorder was still required. Affinity Energy replaced the outdated chart recorder with a new circular chart recorder by Future Design Controls, saving money without compromising accuracy.
Precise Temperature Control
The refrigeration process includes the typical compressor, evaporator and condenser devices. A refrigeration cycle begins at the compressor which pressurizes the gas returning from the evaporator coil in the chamber. This high-pressure refrigerant gas condenses into its liquid state, but can only do so if it can release heat.
As the gas travels through a condenser coil located outside of the chamber, it gives off heat, becoming a high-pressure liquid. This liquid refrigerant travels through an orifice and becomes a low-pressure liquid, which wants to evaporate to a gas, but must absorb heat to fuel the transformation. The gas travels through
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