5th
Reading Power Use… Somehow
2 of a 5 part series
Option 1
There are many options to monitoring power use. One such way is to attach inductive coils around the main power lines to monitor Voltage and Current. There are lots of products on the market that can be used in a residential setting. These products require direct access to the mains power lines, but our commercial electrical closet has a main circuit breaker indicating 4000 Amps. There is no way we were going anywhere near that! Since we did not want to professionally install any expensive equipment for this initial experimentation stage we opted not to go this route.
Option 2
The Elster utility meter has an ANSI C12 Infrared data port on the front (marked by B in the above image) offering the ability to read power measurements from the meter. The hardware protocol is a simple RS232 like-Infrared serial protocol. We initially considered using this data port to read data from the meter but upon talking to NStar about it they told us we were not permitted to attach anything to the meter itself as this would be a violation of the meter lease agreement.
Option 3
The Elster meter has a numerical LCD display of the total watt/hours accumulated by the meter over a finite period of time. We considered implementing an Optical Character Recognition system that would read the values on the LCD with a webcam and convert that to power use. Unfortunately the values seemed to only update on a daily basis. We wanted at least up to the minute resolution so this method was out of the question.
Option 4
After some research on the Elster A3 Alpha utility meter I found that there is a blinking box on the LCD display that has a frequency proportional to the instantaneous power use (marked by A in the above image). Every time the box changes state, this indicates .9kWh (kilo Watt hours) have been used. Finally a feature we can work with! We will watch the blinking box with a web cam on an embedded Linux device and determine the energy use by monitoring the blink rate.
Tune in next week where I discuss the electronics and software design.
Hooray for bureaucracy! There is a perfectly good optical port on the device, which uses light instead of copper to make a signal path (therefore no danger of an external device hurting the meter,) costs money for the manufacturer to include the firmware and circuitry, and is just sitting there, AND WE CAN’T USE IT because someone at NStar feels this would somehow void a lease agreement. Brilliant.
I suspect the IR data port needs to be free so the person who comes by to read the meter can use it, if they happen to have the right device for that.
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