TOKEN IDENTIFIER (TID)
The TID is a 24 bit field in the 66 bit token data that identifies the number of minutes expired since the start of the current base date. The position of the TID is shown below in bold:
= 3148437 minutes
|0010011100010000 (1000 decimal as per amount formula in IEC62055-41)||0001100101110000 (1970 Hex)|
With each bit of the TID field representing one minute, this gives a total duration of 16777215 minutes, or approximately 31 years. This means that the TID rolls over to zero when the one is added to the TID value at a maximum value of the TID field.
Base Dates and meter manufacture
When a meter is manufactured, the TID memory is filled with the date of manufacture so that there is some data in the TID memory. This is normally the number of minutes since 01/01/1993 for a 1993 base date meter.
With a 2014 base date meter, the TID memory of a 2014 base date meter will be filled in with the number of minutes since 01/01/2014.
The maximum number of minutes allowed for TID = 0xffffff = 16777215 minutes.
So, if a meter is manufactured on 01/01/2020 08:00:00 :-
- For a 1993 base date meter – TID memory filled with TID = 14200320 - this is the number of minutes from 01/01/1993 00:00:00 to 01/01/2020 08:00:00.
- For a 2014 base date meter – TID memory filled with TID = 3155520 - this is the number of minutes from 01/01/2014 00:00:00 to 01/01/2020 08:00:00.
The 1993 base date meter only has 16777215 – 14200320 = 2576895 minutes left (4.9 years) until it rolls over (24 Nov 2024 20:15)
The 2014 base date meter has 16777215 – 3155520 = 13621695 minutes left (25.9 years) until it rolls over (24 Nov 2045 20:15)