Usage Accuracy

Technical Questions
8

To: @samheidie

I plotted the Power company readings vs. SENSE readings for 9 months - Daily.

I plotted the ‘kWh difference’ values as a scatter point chart and looked for any trends. Two distinct baselines were observed. (It is hard to see the two dashed lines that show the average baselines on this chart at -0.137 and +0.011)


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I calculated the average for each baseline, then I calculated the ‘offset’ from the baseline. ‘offset’ = kWh difference - baseline average, I plotted those values in a Histogram, Then I summed all the outliers (values that were not close to the bell curve).


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Observations:
On April 23rd, 2018 there was a shift on the offset baseline of 0.148 kWh and has stayed consistently at the new baseline.

  1. On 4/23/2018 I added a TD-69 delay timer relay to my SENSE monitor. At the same time I reworked my CT clamp installation. I used the foam insulation from a ½-inch pipe insulation as a spacer to center my clamps and to position them so that they are 90-degrees perpendicular to the service cable in the breaker panel. When I initially installed the CT clamps (Sept. 2017) they were not at a true perpendicular angle or perfectly centered around the cable. I also taped the CT clamps in closed position, making certain they were completely closed. The new foam insulation ‘spacers’ were not allowing the clamps to remain closed.
  2. My charts indicated that prior to re-positioning my CT clamps, that I could expect a higher number of outlier data points.
    Pre- 4/23/2018: 111 data points with 37 outliers
    Post-4/23/2018: 124 data points with 30 outliers

Recommendations:

  1. Verify your CT clamps are completely closed and at a 90-degree angle to the power (or service) cable when doing your initial installation. Changing the clamp positions may give you a change in the readings.
  2. My SENSE monitor now tracks the same values as the Power Company meter more frequently after making this very minor change. The SENSE unit currently reads an average of +0.011 kWh/day more consumption than my power company meter where previously it read -0.137 kWh/day or less consumption.
  3. SENSE currently tracks the power company meter with an average 0.024 % daily error between the two readings.

I posted this same information with more graphs earlier in:

Does anybody have any cool graphs or analytics using Sense data - Please share!

Data Analysis

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