Maxim Integrated 71M6513H Power Meter IC Family Software - Manual (Page 80)

71M651x Software User’s Guide
5.11.FIRMWARE APPLICATION INFORMATION
5.11.1.Sag Detection
A sag is defined as an undervoltage condition that persists for more than one period. A shorter undervoltage condition
is called a dip (see Figure). The occurrence of sags can announce an impending loss of power. Since accumulated
energy values etc. in the meter will have to be saved to non-volatile memory in the case of loss of power, a sag can be
used to initiate data saving operations. Some applications may instead save or count the sag event for the purpose of
recording power quality data.
dip
sag
Figure 5-22: Sag and Dip Conditions
Sag detection is performed by the CE, based on the CE DRAM registers SAG_THR and SAG_CNT. SAG_THR
defines the threshold which the input voltage has to be continuously below, and SAG_CNT defines the number of
samples required to trigger the sag bit (see Figure 5-23).
16.67ms
SAG_THR
SAG_CNT
84 samples
16.67ms 16.67ms
SAG_THR
SAG_CNT
84 samples
Figure 5-23: Sag Event
When the CE detects a sag that meets the sag conditions specified in SAG_THR and SAG_CNT on one of the input
voltage channels, it will reflect this in the corresponding bit (SAG for single-phase, or SAG_A, SAG_B, SAG_C for
poly-phase) of the CE STATUS Word. See the CE Interface section in the 651X Data Sheet for details.
It is up to the MPU firmware to decide what is to be done in case a sag is detected. The Demo Code does not have
any provisions for actions due to sags detected by the CE.
5.11.2.Temperature Measurement
The temperature output of the on-chip temperature sensor (TEMP_RAW) is stored by the CE in CE DRAM location
0x54. The relative chip temperature (TEMP_X) is derived by subtracting the raw temperature from the nominal
temperature (TEMP_NOM) stored in CE DRAM location 0x11 and multiplying it with the constant factor DEGSCALE
(decimal 22721 for the 6513 and 9585 for the 6511). Thus, once the raw temperature obtained at a known
environmental temperature is stored in TEMP_NOM, TEMP_X will always reflect the deviation from nominal
temperature. The scaling is in tenths of Centigrades, i.e. a reading of 75 means that the measured temperature is
7.5°C higher than the reference temperature.
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