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From: Uwe Hercksen on 26 Jul 2010 10:06


amdx schrieb:

> Here's a power monitor that uses clamp on current transformers.
> I don't see where it monitors voltage, so wouldn't it measure reactive
> power at an incorrect rate?
> http://www.currentcost.net/howitworks.html

Hello,

they write no batteries are to be changed, therefore the transmitter
with the connected clamps should have a power supply. If there is a
power supply, the voltage can be measured too. The display has its own
power supply, it is possible to measure the voltage within the display
and to do the math to calculate power there.

Bye

From: amdx on 26 Jul 2010 11:38

"Uwe Hercksen" <hercksen(a)mew.uni-erlangen.de> wrote in message
news:8b5j2nFp3jU1(a)mid.dfncis.de...
>
>
> amdx schrieb:
>
>> Here's a power monitor that uses clamp on current transformers.
>> I don't see where it monitors voltage, so wouldn't it measure reactive
>> power at an incorrect rate?
>> http://www.currentcost.net/howitworks.html
>
> Hello,
>
> they write no batteries are to be changed, therefore the transmitter with
> the connected clamps should have a power supply. If there is a power
> supply, the voltage can be measured too. The display has its own power
> supply, it is possible to measure the voltage within the display and to do
> the math to calculate power there.
>
> Bye
>
It says on the page I posted above,
"The transmitter's D size batteries should last up to 7 years before
replacement."
There is a video showing installation, it doesn't show any physical
connection to the wiring.
So, my thinking at this point, they measure current, assume voltage and
power factor* and
calculate power with those numbers.

*I send the an email and see if they assume anything other than 100% PF.
Mike




From: Uwe Hercksen on 26 Jul 2010 12:06


amdx schrieb:

> "The transmitter's D size batteries should last up to 7 years before
> replacement."
> There is a video showing installation, it doesn't show any physical
> connection to the wiring.
> So, my thinking at this point, they measure current, assume voltage and
> power factor* and

Hello,

but there is the power supply for the display unit, they can measure the
voltage there and they can do the necessary math, assume the power
factor and assume the second voltage is the same as the measured one.

Bye

From: John Larkin on 26 Jul 2010 12:17
On Mon, 26 Jul 2010 18:06:10 +0200, Uwe Hercksen
<hercksen(a)mew.uni-erlangen.de> wrote:

>
>
>amdx schrieb:
>
>> "The transmitter's D size batteries should last up to 7 years before
>> replacement."
>> There is a video showing installation, it doesn't show any physical
>> connection to the wiring.
>> So, my thinking at this point, they measure current, assume voltage and
>> power factor* and
>
>Hello,
>
>but there is the power supply for the display unit, they can measure the
>voltage there and they can do the necessary math, assume the power
>factor and assume the second voltage is the same as the measured one.
>
>Bye

Cheap "power meters" usually measure current and assume both line
voltage and some typical power factor, like 120 volts and 0.8 for
example. Their current sensors tend to be bad as well.

John

From: amdx on 26 Jul 2010 13:11

"amdx" <amdx(a)knology.net> wrote in message
news:ee3e0$4c4dac05$18d66057$25642(a)KNOLOGY.NET...
>
> "Uwe Hercksen" <hercksen(a)mew.uni-erlangen.de> wrote in message
> news:8b5j2nFp3jU1(a)mid.dfncis.de...
>>
>>
>> amdx schrieb:
>>
>>> Here's a power monitor that uses clamp on current transformers.
>>> I don't see where it monitors voltage, so wouldn't it measure reactive
>>> power at an incorrect rate?
>>> http://www.currentcost.net/howitworks.html
>>
>> Hello,
>>
>> they write no batteries are to be changed, therefore the transmitter with
>> the connected clamps should have a power supply. If there is a power
>> supply, the voltage can be measured too. The display has its own power
>> supply, it is possible to measure the voltage within the display and to
>> do the math to calculate power there.
>>
>> Bye
>>
> It says on the page I posted above,
> "The transmitter's D size batteries should last up to 7 years before
> replacement."
> There is a video showing installation, it doesn't show any physical
> connection to the wiring.
> So, my thinking at this point, they measure current, assume voltage and
> power factor* and
> calculate power with those numbers.
>
> *I'll send them an email and see if they assume anything other than 100%
> PF.
> Mike
>
I got a response back already,
"The units assume 100% powerfactor and a level 120 volts."



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