Accuracy
The accuracy of the energy monitor was tested by comparison with a cheap plug-in domestic energy monitor. A series of resistive and reactive loads were chosen to give 25 data points up to a maximum of 2238W. Voltage, Current and real power values for each load were read from the reference meter's display, the energy monitor serial terminal, and logged in a spreadsheet, from which the error, percentage error and standard deviation of the error were calculated.
It was impossible to record all the values for both meters simultaneously which is a significant source of experimental error. The values would vary significantly from second to second, and it's difficult to say how much of this second to second variation is due to voltage changes in the mains supply, load variations (e.g. as heaters heat up) or due to meter measurement resolution. It would be interesting to test the meter on a professional test apparatus.
That said, the results are an improvement on the previous meter design, and are as follows:
Current
The current was measured up to 9.28A. The absolute error maximum was: +0.01A and minimum was -0.03A
The standard deviation of the error: 0.011A
In the range of 0.6A to 9.28A the percentage error for current stays within 1%
Voltage
Voltage was measured in the range 241V-250V. The absolute error maximum was: +3.7V and minimum was -0.5V
The standard deviation of the error: 1.236V
The graph of voltage vs error shows a definite sloping trend which suggests the result can be improved with calibration.
Real Power
Real power was measured in the range 13.7W - 2238W. The absolute error maximum was: +9.6W and minimum was -2.1W
The standard deviation of the error: 2.624W
There appear to be two possible experimental errors at ~560W. Without these, the max absolute error would be: +3.50W
In the range of 170W to 2238W the percentage error stays within 2%
Apparent Power
Apparent power was measured in the range 39VA - 2239VA. The absolute error maximum was: +6.23VA and minimum was -7.54VA
The standard deviation of the error: 3.898VA
In the range of 150VA to 2239VA the percentage error stays within 2%
Power factor
Power factor was measured in the range 0.45 – 1.00. The absolute error maximum was: +0.03 and minimum was -0.02
The standard deviation of the error: 0.008
In the range of 0.45 – 1.00 the percentage error stays within 3.5%