If your house's electric meter doesn't have a large horizontal disk, read no further.
How can you use your home's electric meter to measure the total power of all the electric devices operating at any given time? This is the question of the [link gone] Watt's Your Power page. (However, that page uses rotations per minute, whereas I find seconds per rotation more convenient. So I wrote this page.)
To find how much electricity your house is using at the moment, use the Kh factor as painted inside the meter, observing how many seconds it takes the large black mark on the horizontal disk to rotate once.
Power(in watts) = 3600 * Kh / seconds_per_rotation
On my electric meter it says the Kh factor is 7.2. With a stopwatch I observe the black splotch takes 300 seconds to rotate once when just the refrigerator is busy. The more appliances working, the fewer the seconds it takes for the disk to rotate once. Sacrificing clarity for brevity, and cleaning up tabs, we program:
$ perl -pwe 's@\d+@int 7.2*3600/$&@e' <<End_of_input 700 just UPS, no computer, refrigerator unplugged 300 refrigerator compressor running 115 refrigerator compressor running; computer and monitor via UPS 207 computer and monitor (not blanked) not via UPS; refrigerator unplugged 20 refrigerator compressor running; water pumps
Seconds_per_rotation become watts in the output. 86 watts when just the refrigerator is on, etc.:
37 just UPS, no computer, refrigerator unplugged 86 refrigerator compressor running 225 refrigerator compressor running; computer and monitor via UPS 125 computer and monitor (not blanked) not via UPS; refrigerator unplugged 1296 refrigerator compressor running; water pumps
So it seems that the particular uninterruptible power supply (UPS) I bought for my computer and monitor only uses 225-86=139 watts, only 139-125=14 more than computer and monitor with no UPS. [Does this sound right?] No wonder it only gives less than 5 minutes of power during outages.
I didn't stick around all 700 seconds, so that is a guess. Also there are some small DC transformers on the line skewing that figure.
In [gone web article] The Theories and Modeling of the Kilowatt-Hour Meter, we see KH is known as the "disk constant" and is the number of watthours measured of each revolution of the disk. Ok, how many rotations till we reach an entire kilowatthour?
Kh=wh/rev; rev=wh/Kh = 1000/7.2 = 138.888..
In fact the meter has an "Rr 13 8/9" painted on it.
From: Dave Dahle, 2003 Newsgroups: misc.industry.utilities.electric, etc.
You're not taking the gear ratio between the disk and register pickup gear into account!
In this case, we can safely assume it's 100 (commonly used on GE, ABB/Westinghouse, and older Sangamo and Duncan meters).
Rr is the number of revolutions of the pickup gear for a full revolution of the rightmost dial.
[So 1000 / 7.2 / 100 = ( 13 + 8 / 9 ) / 10 --Dan]
FM2S means Form 2S - this is just one of a number of standardized styles of electric meters for use on various electrical services (Form 2 is for singlephase 3-wire application). The S means the meter is a detachable version that plugs into a socket assembly - the other option is A for "A-base" which has a built-in terminal block on the base (A-base meters are largely obsolete in North America but standard in the rest of the world).
That just means 'singlephase 3-wire' - the type of service the meter is built for. that symbol is commonly used in the electric utility industry for the word 'phase'.
30 amps for testing (100% load point), 200A is the maximum load it can safely carry (667% overload).
Typically, 30-35 years but I have seen some 1940s meters still in use.
Yes, that 100-mark system is fairly universal, although there are some modern exceptions. The idea is that where the disk is being timed against a standard, you would be able to read to within 1% of a revolution once you stop the test. The standard and meter revolutions are then plugged into a formula to get the meter's accuracy. The timing mark does usually take the last 5% of a revolution... the idea being that the transition from black to silver would tell the counter exactly when each revolution starts.
Let's see, that would be equivalent to a
$ perl -le 'printf "%.1f\n", 40 * 1000 / ( 60 * 24 )' 27.8
watt light bulb burning 24 hours a day.
Last modified: 2015-09-12 19:20:43 +0800