Smart meter backup

The electronics shuts off everything, include the display, and the current needed to back up the status and keep the minimal functions ticking over is about the same level as a digital watch - some hundreds of nano-amps to few microamps, As a consequence  the 'hold over' period compares to a watch, it is at least 30 days, probably more like a year with a brand new meter.

As an aside note that even 'non volatile' memory like flash and EEPROM rely on capacitor-like charge storage, it is just that the capacitors are made with sub-micron volumes of silica inside the chip itself, and these have self-leakage times of many years, and store so little charge it is quite sensible to talk in terms of numbers of electrons.

Mike

The electronics shuts off everything, include the display, and the current needed to back up the status and keep the minimal functions ticking over is about the same level as a digital watch - some hundreds of nano-amps to few microamps, As a consequence  the 'hold over' period compares to a watch, it is at least 30 days, probably more like a year with a brand new meter.

As an aside note that even 'non volatile' memory like flash and EEPROM rely on capacitor-like charge storage, it is just that the capacitors are made with sub-micron volumes of silica inside the chip itself, and these have self-leakage times of many years, and store so little charge it is quite sensible to talk in terms of numbers of electrons.

Mike

mapj1 said:

As an aside note that even 'non volatile' memory like flash and EEPROM rely on capacitor-like charge storage, it is just that the capacitors are made with sub-micron volumes of silica inside the chip itself, and these have self-leakage times of many years, and store so little charge it is quite sensible to talk in terms of numbers of electrons.

I have heard that memory sticks should not just be put in a drawer for decades, but used once in a while.

They use FLASH, and the stored charge does leak with time. However, some devices now quote storage times of getting on for over 50 years at elevated temperatures when the device is new (these are typically microcontrollers intended for harsh environments, such as automotive ECUs). The storage time does decrease as the device is used, as each erase cycle puts stress on the device.

Personally, I would be inclined to use FRAM for something like a smart meter, as this does not suffer from ageing in the same way and is easier to use.