8 Communications – History Data Extraction
29
Initiating Data Retrieval and Controlling the Number of Profiles Sent
To initiate historical data retrieval, a read holding register command is issued to address 0506. The “number
of registers” variable in the read command controls the number of historical profiles to be extracted. Once
the desired number of readings has been found and transferred the transmission ends.
Historical Data Profile Structure
The historical data is transmitted in frames consisting of 48 bytes each. The frame structure is shown
in the table below.
Data profile information, except RTC, kWh and VAh, is saved in 16-bit floating point format using truncation
of the least significant decimal information. To increase resolution from truncating data for storage, each
part of the profile has an associated multiplier. When data is extracted, first make the 16-bit value into a 32-
bit float by appending 0x7FFF and then multiply by the multiplier. VAh and kWh are stored as 32-bit floating
point numbers and do not need a multiplier.
As an example of using the multiplier, assume the phase A voltage reading is 276.7 V. This value is divided
by the multiplier (100) to become 2.767 (0x40311687) and is stored in the data profile as 0x4031. When
translated back from hex to a float, 0x40317FFFbecomes 2.7734, and using the 100 multiplier gives a
value of 277.34 V. This data condensing is used to increase storage capacity, and does not affect long term
meter accuracy. The running kWh and VAh totals are a combination of two floating point numbers, which
maintains accuracy beyond thousandths of a kWh, even when high values are reached.
Frame Item
Size (bytes)
Multiplier
Meter Address
1
n/a
Function Code (0x03)
1
n/a
Profile Memory Address
(decreases with each frame)
2
n/a
Time of use Year
1
1
Time of use Month
1
1
Time of use Day
1
1
Time of use Hour
1
1
Time of use Minute
1
1
WEB
VERSION
Содержание 3300 series
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