Cube Energy Application Module (EAM)
IntroductionThe Energy Monitor is intended to provide monitoring points that accurately measure energy consumption by high use devices. In the home this might be used to monitor highly variable loads like A/C, electric SPAs, and electric furnaces. An additional unit might be used to monitor the energy consumption of the whole house. Because many of the high load devices are used to heat or cool various substances like water, air, or refrigerant; the Energy Monitor will also include temperature and humidity sensors. The Energy Monitor provides the user with valuable data that can be used to evaluate the effectiveness of various cost saving experiments around the home. It might also be used to monitor the efficiency of devices, like an A/C compressor, house insulation, or a SPA cover, that deteriorate over time and require maintenance to ensure peak performance.
The Freeduino Cube platform provides the base for the Energy Monitor. The Common Compute Module (CCM) provides software application endpoints for energy, temperature and humidity. These application endpoints are accessed using any of the available Freeduino Cube Bus Modules (BM).
HardwareThe Energy Monitor hardware is broken down into several major blocks; Freeduino Cube Common Compute Module (CCM), Bus Module, and Energy Application Module (EAM). The Energy Application Module contains energy calculation hardware, current / voltage sensors, AC power module, and 2500V galvanic isolation. The EAM is the primary hardware component described here. Other Freeduion Cube modules are described in other Cube sections.
Accurately measuring energy can be difficult because most loads are not purely resistive. Capacitive or inductive loads require more complex measurement techniques. In recent years a number of integrated circuit devices have been created that combine all the required elements to perform complex energy calculations. The Energy Monitor uses one of these highly integrated devices from Analog Devices ADE7753.
Current and voltage sensing in the Energy Monitor are designed for higher power loads. The use of current transformers allows the Energy Monitor to have an operating current range from a few amps to hundreds of amps. The exact range can be tailored for each monitored load with the selection of suitable current transformers.
Power in a Freeduino cube platform is normally provided by a separate Power Module (PM). However the inherent isolation requirements of the EAM leads to a design where the EAM also provides the functionality of an AC Power Module (ACPM) along with 2500V of isolation that is inherently required since the electronics of the EAM are directly tied to the AC mains. Both the CCM power and I/O lines are isolated on the EAM. This makes it safe to connect the CCM using any of the wired Bus Modules and also isolates any one-wire devices connected to the CCM from the AC mains. If a wireless Bus Module like the Zigbee Bus Module (ZBM) is used, then the one-wire sensor chain is completely isolated and safe for use where the sensors might come into direct contact with water (e.g. SPA temperature sensor).
As implemented the Energy Monitor is suitable for measuring energy consumption of 120V/240V, one or two phase devices making it ideal for residential and light commercial applications. Similar energy measurement integrated circuits exist for 3 phase energy measurements ADE7754. A second Energy Application Module design could implement 3 phase measurements to extend the Freeduino Cube EAM to commercial and industrial applications.
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