As the cost of electrical power increases, the desire to use less energy also increases and the need to measure power consumption becomes a necessity. Reduction of energy use starts with knowing where the use occurs.
Electrical energy is measured in watts over time. There are many methods to measure electrical power but all have common features. To measure watts in an alternating current circuit, the supplied voltage is compared with the current, and whether the current peaks before the voltage (leading power factor in a more reactive circuit) or the current peaks after the voltage (lagging power factor in a more inductive circuit), the real power is measured.
The old spinning disk and dial indicating watt meters supplied by the serving utility are being replaced by electronic “smart” meters, but they only provide information about the entire service consumption. To monitor individual loads or processes in industry, or more specific consumption in office buildings, watt transducers or monitors can be installed. The purpose is to obtain information regarding more precise information at each installation. This information helps to isolate potential problems such as phase loss or voltage sags and voltage spikes, unbalanced current phase to phase, and can help to avoid utility surcharges levied for poor power factor.
NK Technologies’ New APN Series Power Monitoring Sensors
NK Technologies’ new APN series of power monitors is a big step forward from analog signal reporting watt consumption to a digital format allowing information on the system voltage, current, and power factor along with wattage. The RS485, Modbus RTU format is compatible with many programmable logic controllers and fits seamlessly into industrial communications networks, both hard wired and wireless depending on the specifics of the application.
The APN can be configured to accept standard 5 amp current transformer inputs or sensors producing 333mVAC proportional to the AC current of the circuit, or they can use factory matched Rogowski coil inputs. The primary circuit voltage is connected directly to the monitor for 600VAC or lower, or through a potential transformer for monitoring circuits of higher potentials.
The APN is powered from an external supply, improving measurement accuracy of the measurement data. The APN series also provides a pulse contact which opens and closes as watt hours are accumulated. This feature allows for a less complex data acquisition device for applications where the need to monitor circuit voltages or the other data points is minimal
Monitoring Air Conditioning System Power Usage
NK Technologies’ has installed APN monitors to measure power use by the air conditioning system as part of its efforts to reduce power consumption at its factory. A data acquisition system designed and built by its engineering staff was also installed.
Five APN sensors are connected to the 120/208 volt power feeding the AC units mounted on the roof of the building. The pulse contact reports watt hour usage to counters made by Dataq Instruments (DI-160). This information is read at regular intervals, allowing auditors to know power consumption of each AC unit. In addition, the APN monitors are also connected via Modbus RTU to an internal wireless network using NK Technologies’ WRT transceivers. This allows the details regarding power use to be seen and power usage analyzed at any time.