# electricity monitor

• posted on October 21, 2010, 7:45 pm
I have a british gas electricity montor as I think my electric consumption is to high, we live in an average 3 bed semi. At the moment it is reading energy being used at 900watt. There dosn't seem to be a setting that i can match day by day the usage on the monitor together with the digital electric meter. I have to pay £80 if I want the meter tested and wondered if anyone has tried an energy monitor before? and how reliable are they?
Chris
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• posted on October 21, 2010, 10:41 pm
wrote:

That suggests to me that you don't know the difference between power and energy, and that this is probably the source of your confusion ...
Power is the RATE of consumption of energy. Scientists use the units Joule for energy and Watt for power:     1 W = 1 J/s
However, these units lead to rather unmanageably large numbers when applied outside the laboratory to everyday matters such as consumer electricity consumption. Hence the kW is the normal unit of power, and on your bill the kWHr the normal unit of energy.
1 kW    = 1000 W &    1 kWHr    = 1 kW sustained over one hour             = 1000 * 60 * 60 J             = 3,600,000 J             = 3.6 MJ
Therefore, all your equipment in the house at the moment that you took the reading was consuming electrical energy at the RATE of 900J every second. Doesn't seem excessive to me. Some examples:
PC:                    200 - 500W Incandescent lamp:    40 - 100W (250W for a standard lamp) Energy Saving light:    8 - 12W Fridge/Freezer:        125W

That's because the monitor is measuring rate of consumption in W and the meter is measuring energy consumed in kWHr over the period of time since whenever it was set to zero, either when it was manufactured or when it was installed.
To relate the two figures, first calculate the energy consumed over a period of time by subtracting the meter reading at the start of the period from that at the end. This gives you a figure in kWHr, so multiply it by 1000 to get WHr, and divide it by the number of seconds in the period of time to get the average rate of consumption over the period in W. The result should then be fairly close to the monitor readings during the period, allowing for the fact that things like fridges switch on and off under their own control.

See if you can relate the figures given the above information.
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• posted on October 21, 2010, 10:56 pm
On reflection, the calculation quoted is wrong. It should be:     (Meter2 - Meter1) * 1000 * 60 *60 / (secs in period)
So, as you can see, the calculation is sufficiently complicated that even those of us with a good scientific education can easily make careless mistakes when it comes to the non-decimal everyday units!
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• posted on October 26, 2010, 12:02 am
I've got an Owl meter and I've used the Owl's predecessor - the centometer - and another one that I can't remember the name of.
Generally I've found them fairly accurate. The Owl I'm using now is quite good. It keeps a running total of the kW used, but this should only be used as a guideline as there may be times when it doesn't pick up the signal and so won't be recording anything.
The Owl seems to be a bit more sensitive than previous ones I've used, but you may find that these sort of monitors aren't very accurate at very low wattages.
If you want to try it for accuracy, switch something on that you know the rating of - e.g. a 2 or 3kW kettle, or a 1kW fire - and compare the meter display before and after you turn the device on (but be aware that anything else you're running that starts up when you're monitoring could affect the reading, so try it again if it doesn't seem right.
Roger

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• posted on October 26, 2010, 1:29 pm
However, be aware that the ratings on things like kettles are rather nominal - if it's a rounded figure 1kW could be anything between 501W and 1.49kW!
On Mon, 25 Oct 2010 19:02:31 -0500, snipped-for-privacy@cix.compulink.co.uk wrote:

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• posted on October 28, 2010, 9:42 pm
I'd forgotten that.
I see that Owl have now brought out the Owl+USB - the all-in-one for storing and downloading the information onto a PC. I've got the separate USB receiver, but the downside to that was that it would only work when the PC was on, and I certainly wasn't going to leave the PC on just to monitor my electricity usage!
Roger

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• posted on November 6, 2010, 10:03 am
AS a follow-on my previous comment, I've now got the Owl+USB. Ideal and does exactly what I want. A few comments on what I've found over the past few days since I've used it:
The data is downloaded when you connect the monitor to the PC or, if you have the monitor permanently connected, when you open the programme. What I like about the PC connection is that it lets you see exactly what you've been using at any point in the day to the nearest minute.
The monitor is the same as the previous Owl, with the same functions and easier to set up, but with the addition of a USB socket.
The Owl+USB is ideal for anyone who wants to see the historical information in more detail than the monitor itself can show. Unlike the monitor, that only shows the last day, last week, last month etc., the PC allows you to look at any minute since the programme was installed. It's also useful if you want to see just how long something large has been running. (a large item is clearly seen when it's switched on as a sudden peak above the normal reading). This is useful for seeing when an immersion heater has cut in during the night (an average of about 5 mins every two hours), or when storage radiators have been in use during the night, for example. Even for other things such as how long an electric shower has been on and its cost (7½ minutes and 14p!)
Roger

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• posted on November 6, 2010, 5:22 pm

I'm considering using one of these to monitor my solar Panel generator system. Please can you tell me if it is possible once the data has been downloaded to the PC, whether their software allows it to be exported into MS Excel spreadsheets.
Bob
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• posted on November 7, 2010, 12:50 am
snipped-for-privacy@YOURHATntlworld.com (Bob Minchin) wrote:

Yes It exports the data as a CSV file and you have three options: The last 2 mins usage at 6 second intervals Data within a start and end date range - 1 min intervals All data - 1 min intervals
You don't have an option to change the interval times, which means you have 1440 lines for each 24 hour reading!
You also have to do some conversion of the data if you want it to show in true mode like it does on the PC. E.g kW has to be divided by 1000. If the output is shown as 60.48, it is in fact - 0.06048 kW that has been used in that minute.
When you're looking at it on the PC screen, you "drill down" to get to what detail view you want by clicking on the display. It starts with the bar chart column for the years, then the months, then the day, then the hour. The hour display is broken up into 60 x 1 minute columns.
Whatever detail you're in, hovering over the column with the mouse will show you the total for that column.
There is a manual on the Owl site - look for the logo at the bottom of the page, although this is not the software manual: http://www.theowl.com /
Roger
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• posted on November 21, 2010, 9:29 pm

You might want to be specific about the model, because the OWL USB I bought a couple of years ago can't do that, and is almost completely useless.
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Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
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• posted on November 28, 2010, 6:42 pm
It's actually called Owl+USB on the box and on their site http://www.theowl.com/index.php?page=owl-usb
There's no model no. on the Owl display unit, but it shows up on the computer as model no. CM160.
The display looks exactly the same as the CM119, the only difference is that it has a mini USB socket on the side.
I assume you has the Owl USB Connect which was the black receiver that connected to the PC. I've got one of those and it worked OK, it just meant that the PC had to be running all the while (which made it totally useless!). It was better when they finally updated the software (available on the Owl site)
I've had the Owl+USB for a month now, and I can't fault it. If you like the principle of the Owl USB connect, then I recommend this one. As long as you connect the Owl+USB to the PC within every 30 days (or it will start overwriting the data in its built in memory), you will have a continuous minute by minute record of the electricity used. This can be exported as a CSV file (the whole lot, that display, or from X to Y dates).
I have the owl permanently connected to the PC and so it automatically uploads the new data every time I open the programme, which is normally once or twice a day.
Roger