I have one of the relatively modern electricity meters with a digital
display and when I went to read it today to send in the reading, the
display was reading alternately the power consumed and "rEd".
Additionally a red led is permanently on.
The make of the meter is 'Ampy' - Black and about 100 x 150 x 40mm
Can anyone confirm what this means please?
I have recently had a solar PV system fitted which can feed power back
into the grid. The meter was not changed to accommodate this (instead I
have my own generation meter) so I wonder if it is just an indcation
that the meter has tried to run backwards which would normally happen if
someone was trying to fiddle the meter reading but in my case just shows
the Solar PV has been generating more power than I have been consuming.
I know it is bad form to reply to your own posts but it might help someone.
I have found the answer here
The red light either flashes every 1 watt-hr consumed or stays on
continuously when the power being consumed is below a preset level.
The display flashing rEd is showing "reverse energy detection" which
would normally mean fraudulent use but in the case of power export from
microgeneration schemes (PV, wind etc) is legitimate.
In my case, when the light is on continuously it means that I am
generating more power than I'm using - this is confirmed by the display
reading now being identical to the one I took 8 hours ago.
According to the manual, the meter has a separate register measuring
exported power although the reading is not displayed.
On Apr 20, 5:10 pm, Bob Minchin
All the meters data is recorded in a Ferroelectric Random Access
Memory (FRAM) under the control of the microprocessor. All the kWh
registers are stored in the FRAM and are updated every 1/100 th of a
kWh. The FRAM is guaranteed for a minimum of 10,000,000,000 write
WTF? Core memory?! 8-)
Yes I found that difficult to credit but I suppose it maybe used to meet
a possible regulatory requirement for N years retention with no power
Having looked further, I think it is the 10,000,000,000 write cycles
that makes it ideal for this application to cope with the update rate.
It's been around for quite a while. FLASH and EEPROM are mostly
useless for this type of application. Given it's an electric meter
they could just use low power SRAM with a super cap backup supply.
Too easily corrupted. Fe RAM has indefinite data retention after removal
of power, better than 10^^15 write cycles, and a glitch during writing
won't corrupt the rest of the data (According to the makers...)
My point stands.
The warning, "may", is due to potential corruption of the card's file
system that isn't designed to be robust enough to withstand corruption
of a single critical memory location. The data is still there if you
have the right tools to recover it.
FAT filesystems can't be made safe in this way because they require
multiple sector updates to be made simultenously, to remain self
consistent. They have a common delayed action corruption mode where
you can read all the data OK after an interrupted operation, but latent
inconsistent spacemap update results in data corruption sometime
later on when the filesystem is written to again. Also, because there
are so many different implementations of FAT filesystem drivers which
do things in different orders and may not use the clean shutdown bit,
it's not easy to spot this without doing something like a full chkdisk
operation, which appliance devices usually don't implement, nor have
the time to do.
[email address is not usable -- followup in the newsgroup]
It had some interesting faults.
I killed the development of bubble memory cards on SystemX by designing
something far better to replace them.
Cheaper, more reliable and five times as fast tends to kill the competition
Its still in use now and its more than a decade (or two) old.
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