A measurment error?

[amdx]

Hi Guys,

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

Mikek

 

[Phil Allison]

"Robert Baer"

By definition, a CURRENT transformer cannot measure or indicate power.

** Under circumstances where the AC supply voltage is known and PF is likely
to have only a minor effect on the total energy consumption - it most
certainly can give useful indications.



..... Phil

 

[Uwe Hercksen]

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

 

[amdx]

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

 

[Uwe Hercksen]

"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

 

[amdx]

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."

 

[amdx]

John

Yes John, it is the simple way to do an inaccurate measurement that is
easy for
an inexperienced homeowner to hookup.
Although they already have the homeowner inside the circuit breaker panel
putting the clamps around the feed lines, it would not be much more
difficult
to stick a wire in a circuit breaker and another in the neutral bar. BUT now
they're getting into rules and regulations.
It's always something!
MikeK

 

[Uwe Hercksen]

Although they already have the homeowner inside the circuit breaker panel
putting the clamps around the feed lines, it would not be much more
difficult
to stick a wire in a circuit breaker and another in the neutral bar. BUT now
they're getting into rules and regulations.

Hello,

it would have been easier for the homeowner if they put the voltage
measurement within the display unit.
But for a correct measurement three wires are necessary to measure the
two voltages on both phases.

Bye

 

[amdx]

--
MikeK

Hello,

it would have been easier for the homeowner if they put the voltage
measurement within the display unit.

It would be easier, but if it was plugged into a heavily loaded line it
might
drop 2, 3 or 4 volts and there goes the accuracy. Getting current phase at
the circuit breaker box and voltage phase at the display and making a
comparision of phase shift thru an RF link ? I think that's asking for more
error.

But for a correct measurement three wires are necessary to measure the two
voltages on both phases.

I figured someone on this group could do it with just two wires, I
think the 180* phase shift between L1 and L2 is pretty constant.
MikeK

 

[Phil Allison]

"Robert Baer"

"Indication" is *not* "measure".

** Yes it is, you stupid pedantic twat.

And try reading your own words.


...... Phil

 

[Uwe Hercksen]

I figured someone on this group could do it with just two wires, I
think the 180* phase shift between L1 and L2 is pretty constant.

Hello,

a pretty constant phase shift of 180 degrees does not guarantee a
constant voltage ratio of 1.000 between L1 and L2. The load is not very
well balanced between L1 and L2 for all time of the day.

Bye

 

[amdx]

Hello,

a pretty constant phase shift of 180 degrees does not guarantee a constant
voltage ratio of 1.000 between L1 and L2. The load is not very well
balanced between L1 and L2 for all time of the day.

Bye

Noted,
MikeK