On 16/11/2020 18:07, Andy Burns wrote:
Roger Mills wrote:

Dave Liquorice wrote:

The CurrentCost one http://www.currentcost.com/products.html has a
TTL serial output

I got one of them free from e.on (together with USB/serial converter cable)

Is that showing true watts, or simply volt-amps

You don't get billed for watts, just volt-amps

Absolutely wrong, you get billed for watt (hours).

The electricity meter is a very curious device.
The mechanical one...

"The disc is acted upon by two sets of induction coils, which form, in
effect, a two phase linear induction motor. One coil is connected in
such a way that it produces a magnetic flux in proportion to the voltage
and the other produces a magnetic flux in proportion to the current. The
field of the voltage coil is delayed by 90 degrees, due to the coil's
inductive nature, and calibrated using a lag coil.[16] This produces
eddy currents in the disc and the effect is such that a force is exerted
on the disc in proportion to the product of the *instantaneous* current
and *instantaneous* voltage. A permanent magnet acts as an eddy current
brake, exerting an opposing force proportional to the speed of rotation
of the disc. The equilibrium between these two opposing forces results
in the disc rotating at a speed proportional to the power or rate of
energy usage. The disc drives a register mechanism which counts
revolutions, much like the odometer in a car, in order to render a
measurement of the total *energy* used."

Obviously *electronic* meters can do far far more also than just
measuring current, as well! Rapid sampling of voltage and current
enables true energy consumption to be calculated.

--
Climate Change: Socialism wearing a lab coat.