Measuring electricity usage at the meter

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berkinet
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Measuring electricity usage at the meter

Postby berkinet » Thu Aug 08, 2013 9:37 am

My electric meter has an LED that flashes once for each wH (watt hour) of usage. I should be able to count the flashes and then be able to measure actual usage. The question is.. are there Phidgets sensors, boards that can do this.

My service is 230VAC at 45 amps. Normal usage is under 40 amps, or around 10kWh. I calculated (I.e. I could be wrong) 1 wH every 360ms (2.7 wH per second) at maximum usage.

I have a test lashup with an old 1105 light sensor and an InterfaceKit on an SBC. In theory, the ifKit at the 16ms web-service scan rate should be fast enough. I am not as sure about the 1105 - though all it has to do is detect a binary change. Right now I am assuming any value over 12 is "On."

So, any thoughts, or ideas? Are my calculations way off? Has someone done this before? Any help appreciated.

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Patrick
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Re: Measuring electricity usage at the meter

Postby Patrick » Thu Aug 08, 2013 10:11 am

The real question is not how often the LED flashes, but how long it stays on for during the flash. If you have an SBC2 or SBC3, you can measure the analog inputs at 1ms intervals if you run your program on-board - the SBC1 will only give you 16 ms accuracy - and of course this is the same for over the webservice. You will just have to log some data and see what the LED flashes look like. You may want to run your software on the SBC, in order to not lose track of flashes in the event of a network interruption, or your client PC being shut down - I imagine you would like to keep your virtual display in sync with the meter.

You'll want to control ambient light with some sort of hood.

I have some real interest in this type of monitoring. I have AC current sensors installed on the mains lines coming into my house, and measure the power usage directly with these - interesting to compare my measured usage with what the electric company says. This also gives nice realtime power readings. I also wanted to measure my water usage by watching an orange dial rotating, but I haven't been able to detect this consistently with a Phidget.

I'm a bit jealous of your 1105 - this is one of the few Phidgets which we don't have in our archive.

-Patrick

berkinet
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Re: Measuring electricity usage at the meter

Postby berkinet » Thu Aug 08, 2013 10:33 am

Oops, don't be jealous. I was wrong, its an 1127. I also have a spare 1143 I could use.

As to the rest of your post... I have the sensor well hooded with the sensor directly touching the LED.
I can't really use the SBC3's connection to the ifKit since I access it from the network. But, I have an older 1018 I could plug into the SBC and access it over USB. If that works, I could replace the 1018 with a 1011.

BTW, my ultimate goal is to do as you suggested, count pulses on the SBC and then update my remote software (Indigo) periodically.

So. do you think the 1127 is fast enough? I saw an old post about removing a capacitor on the 1105 to increase response time. Is that hint applicable to the 1127 as well? I also just noticed that the 1143 has a much faster (0.5ms) response time. Maybe that is the way to go. I'll give it a try as well.

BTW, for the rotating dials, some are magnetic and a hall-effect sensor might work.

berkinet
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Re: Measuring electricity usage at the meter

Postby berkinet » Thu Aug 08, 2013 11:25 am

Ok. I switched to the 1143 and am seeing pretty fast response times, still using the web-service.

I had some problems with hooding the unit until I realized light was entering the meter through the LCD usage display. A quick cover over that solved the problem. The 1143 seems to do a pretty good job tracking the rise and fall of the LED brightness. Below is a sample of a few cycles at about 1500ms per cycle. Sensitivity was set to 2 and the readings are unprocessed 0-1000 output.

I'd like to have a little wider range between on and off, but right now I am using 65 as a threshold and it seems to work. I might try setting it a bit higher - faster pulsing might not drop the brightness as much between pulses.

Code: Select all

  EDF test                        edf = 53.0
  EDF test                        edf = 57.0
  EDF test                        edf = 64.0
  EDF test                        edf = 72.0
  EDF test                        edf = 68.0
  EDF test                        edf = 66.0
  EDF test                        edf = 64.0
  EDF test                        edf = 62.0
  EDF test                        edf = 60.0
  EDF test                        edf = 58.0
  EDF test                        edf = 56.0
  EDF test                        edf = 54.0
  EDF test                        edf = 68.0
  EDF test                        edf = 72.0
  EDF test                        edf = 70.0
  EDF test                        edf = 68.0
  EDF test                        edf = 66.0
  EDF test                        edf = 64.0
  EDF test                        edf = 62.0
  EDF test                        edf = 60.0
  EDF test                        edf = 58.0
  EDF test                        edf = 56.0

berkinet
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Re: Measuring electricity usage at the meter

Postby berkinet » Thu Sep 05, 2013 4:21 am

Progress report:

I have been running this lash-up for about a month and, so far, it actually seems to work... quite well at that. I added an external app that detects and counts the pulses from the 1143 (a pulse is defined as lux becoming > 65 -- 1 pulse = 1Wh) and displaying the total Wh for the previous minute.

The major problem with the system was that I did not get a real-time view of consumption. So, today I added a 1054 counter to the system. I modified the script noted above to close a digital output on the sbc/ifKit for 10ms and connected the output to the 1054. Boom, I have a frequency count. Then, I just multiply the frequency * 60 to get a real-time display of wH consumption. (Actually, it is not quite real-time since the 1054 only updates on receipt of a pulse - roughly 1 per second depending on consumption.)

The nice thing about this approach (running code on a MacMini and connecting via the web_service) is that I can easily integrate this information into my HA system (Indigo).


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