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Our electric service (USA) is metered with an Elster REX2 digital smart meter. There is a main display area that cycles through some lines of information, most importantly the total energy used. Below the main display is a double-headed arrow made of three elements (it looks something like ◀︎ ■ ▶︎). The arrow flashes slowly or quickly to indicate direction and rate of energy flow—the arrowhead flashes on and off relatively quickly, and the central box flashes less often.

I'm wondering what exactly those flashes indicate. Is the arrowhead one watt and the central box ten? Or is it ten and fifty? Fifty and 200?

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  • Those meter are programmable and the displays can be changed. Contact your power company and ask for the information.
    – JACK
    Jul 21 '20 at 19:20
  • Thanks @jack but after finding the info on these meters and only getting down votes , I Can’t give a upvote fore a good comment.
    – Ed Beal
    Jul 26 '20 at 3:38
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According to the manual the arrow box arrow are real energy indicators Of 3.2 Rex meter tech manual

They pulse at a rate proportional to the rate of consumption. Each square pulse indicates 1kh. each change of state on to off indicates 1/2kh.

The arrow toggles for each Ke Left arrow energy received Right arrow indicates energy delivered. It said see table 2-1 for ke values per meter form. Form 1s, 2s, 12s. ke.1 kh1.0 Form 3s, 4s ke. 0.01 HK 1.0

So it depends on the meter form The different forms are the class meter 20, 200, 320 2 wire or 3 wire single phase and if there is a disconnect link.

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  • I'm not looking at it but I believe it's a 200-class meter, form is 2s. The service is 240V split-phase (two phases). What does "kh" stand for, do you know?
    – randomhead
    Jul 24 '20 at 23:32
  • Kh stands for kilo what hours, or 1000 watts for an hour is 1 Kh . In old light bulb terms a 100w lightbulb x10 turned on for 1 hour is 1 Kh ,today it takes a lot of lights if LED’s to produce the same power usage for light. But turn an electric oven on and watch the meter spin, same with electric water heaters while they are heating the water. code requires water heaters to be rated at 5000 watts so if a water heater was heating at full power for an hour you could see it could consume 5kw per hour of use , lucky we don’t have the hot water running all the time but I hope this example helps.
    – Ed Beal
    Jul 25 '20 at 0:04
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    I know what kilowatt-hours are but I'm used to seeing "kWh" rather than "kh", that's why I asked. And I'm 100% certain that the flashes are too fast to be any appreciable fraction of a kilowatt-hour. Probably like @JACK said the meters are customized by the utility company.
    – randomhead
    Jul 26 '20 at 3:18
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    Kh is a watt hour constant and is equal to the number of watt hours per pulse or rotation of the meter disk. You know I didn't DV. You got 99% right+1
    – JACK
    Jul 26 '20 at 13:51
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    @randomhead The Kh is usually printed on the meter (mine is 10.0 on a smart meter and was 7.2 on my old disk meter). It's how many watt hours are used per pulse. If you time the number of pulses in seconds, the watts you're using = (3600*pulses*Kh) / time (in seconds) = watts. Keep in mind, it's watts, not kilowatts.
    – JACK
    Jul 27 '20 at 12:37
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From the technical manual for the A3 ALPHA, a similar Elster meter:

The real energy indicators blink at a rate proportional to kWh consumption. The center square indicator will blink to indicate pulses of Kh. Each square indicator pulse (turns on and off) indicates 1 Kh. A single transition (on–to–off or off–to–on) indicates 1⁄2 Kh. The left and right arrows blink at a faster rate representing Ke. Each arrow pulse (turns on and off) indicates 1/12 Kh energy measurement. This means that a single transition of an arrow pulse (off–to–on, or on–to–off) represents 1/24 Kh. The left and right arrows indicate energy being either received or delivered, respectively.

Kh should be printed on the front of the meter; on mine, it's 7.2.

So each on-off-on cycle of the right arrow of my meter means my house used (7.2 Wh)/12 = 0.6 Wh of energy, and each on-off-on cycle of the square means 7.2 Wh.

To measure current power, you'd take a stopwatch and time one of those transitions. e.g. I just measured 20 seconds for half a cycle of the square, so that's

7.6/2 Wh × (3600 sec/hr ÷ 20 sec)
= 3.6 Wh × 180 h–1
= 648 watts.

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  • That makes a lot of sense! Despite what Ed Beal said, it seems very difficult to find a PDF of the actual user/technical manual for the REX2; the only thing I've been able to find is the installation manual. I would like to see a link to the REX2 manual before accepting this answer, to know the actual relation between K_h and the flash rates.
    – randomhead
    Jun 1 '21 at 23:21

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