Power and Energy Monitoring transducers from Logic Beach

WNB-P Energy Meter
installed in Residential Service

Logic Beach offers a number of kWh transducers for energy measurement on single to three phase electrical systems. For applications only requiring Power (kw)or Energy (kWh)measurement, the deployment of a ‘pulse output’ meter is a simple and low-cost solution.

Energy and Power
Energy is measured in Watt-hours or kilowatt-hours and is a function of Watts (power) integrated over time. Power is measured in Watts and is a calculated value based upon the measured values of AC voltage and current. Power is sometimes referred to as ‘Demand’ indicating the momentary power level being sourced.

Energy Meter Theory and Installation
To measure Energy consumption of a load, one to three AC current transformers (CT) are placed around the current carrying conductors and voltage sensing leads are attached to the voltage conductors. These CT’s are typically self-powered (by transformer coupling) via the AC source to which they are connected. Most applications of these devices use ‘split-core CT’s which allow for installation of the CT’s around the phase conductors without disconnecting the conductor. Internal electronics accumulate the Watts over time and then output a short switch closure (typically a momentary turn on of a transistor) which corresponds to a predetermined number of Watt-hours.
The number of Watt-hours per pulse is found in the specifications for each kilowatt transducer. In many devices, the transducer’s correlation of pulses to Wh can be adjusted in the field or at time of order. For example, 1 pulse could be scaled to output after 100 Wh of energy has been measured.

This switched output is then simply connected to a digital input configured as a ‘Counter’ on one of the Logic Beach data logging instruments. In many cases, the Counter input channel will be configured with an ‘active pull-up’ which provides the excitation current to be ‘opened’ and ‘shorted’ by the transducer’s switch output… resulting in a ‘high’ or ‘low’ pulse which is counted by the Counter input channel.

Using HyperWare a user will build a program [Example Energy Logging Program] and upload it to the data logger where it executes. The data logger will then count the number of pulses generated within a specific period of time (e.g. 15 minutes is common for utility related studies), scale and typically convert to kWh units. This kWh value can then be sent to data logger memory for a record of power consumption over that time period. Additionally, the flexibilty of HyperWare allows for the program to be expanded to include hourly, weekly, daily, monthly total consumption… and much more.

Energy Meter Application
Chilled water production is a typical application illustrating the use of a kWh sensor and a Logic Beach data logger. Energy consumption in kWh, can be totalized and recorded every 15 minutes as well as the inlet and outlet water temperatures and flow rate of the chilled water. Heat transfer in BTUs can then be calculated and plotted against electrical energy consumption drawing an energy efficiency picture for the system. Using HyperWare, the BTU calculations and even the net energy efficiency can be easily programmed into the data logger.