Power meters (Part 1)

Yesterday’s electric meters were mostly electromechanical meters. They were measuring consumption, they required a technician to read the past power consumption, diagnose them and change their parameters such as power ratings

Today’s electric meters are communicating meters, which means that they can receive and send data without the need for the physical presence of a technician. Installed in end-consumer’s properties and linked to a supervision centre, they are in constant interaction with the network. This is what makes them “intelligent” (this is what they say). Part of the possible interactions is the power shut down if you do not pay your bills, or in case of major network failure in order to prevent the dominos effects…

We heard a lot of objections about these new meters: some had their computers destroyed, some blame the accuracy of the power readings, etc. To be honest, I have no major objections about the induced consequences of the installation of such smart meters. However, I a strong concern about the use of the data collected from the use that we make of electricity: how, when, how much, which equipment (easy is you use the amps signature). I mostly agree with what is written in Canard PC . I will address this matter later.

Tadaaa, last week week, we had a smart meter installed. A flashing green Linky meter made in the local Itron plant. And obviously, it did not take long before I had a look at this new toy and tried to get as much as it is supposed to provide to customers.

Firstly, I gathered a couple of technical documents which anyone should read before doing anything serious and safe. Although the user interface as been carefully designed in order to avoid any reciprocal disturbances between the power line and the customer link, let’s remember that we deal with real power.

Getting access to the “TIC” (Télé Information Client) is easy: just remove the green cover and locate the button which controls the push buttons of the header

Warning: Although the technical documents specify that the TIC can handle high voltage, do not mix the C1 and C2 ports with the I1, I2 and A ports from the TIC.

Connecting individual wires is not so easy as the push button drives the three ports simultaneously…

This is what Itron agreed for the specifications of the meter:

From this ugly picture, you are supposed to understand that the TIC signal is an amplitude modulated signal (AM) using a carrier frequency of 50 kHz (not 50 Hz !). If the amplitude lies between Vevh0 and Vevl0, the corresponding data bit equals 0; if the amplitude lies between 0 and Vevl0, the corresponding data bit equals 1.

Next is an illustration from the real world showing a bit “1” followed by a bit “0”:

The signal is almost 6 V pp and the frequency is 50 kHz (pretty noisy, featuring plenty of harmonics).

Last not least here are a few words about the “A” port which is barely described. The Linky meter specifies that the voltage between “i1” and “A” (unloaded) is 13 V rms maximum, while under a typical resistive load ranging from 225 and 335 ohms, the voltage between “i1” and “A” (loaded) is 6 Vrms ± 10% @ 50 kHz resulting in a minimum of 130 mW available to feed some remote electronics. The signal between “i1” and “A” (unloaded) looks like the one illustrated below: a noisy square signal @ 50 kHz:

I will cover in the next post the way we can use this “i1”, “i2” and “A” lines.

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