User Guide

Practical Theory: Understanding How Data is Stored
9-2
9.2. Data Storage in the BDS
Data in the BDS is stored in nonvolatile SRAM memory, which retains about nine month's
worth of typical data. Collected data is stored until transferred to the Central or Local
computer. This same memory stores setup and calibration data, which is backed up to the
Central or Local computer during initial setup; this process is called synchronizing. Flash
nonvolatile memory stores uploads of new BDS firmware. You can upgrade the firmware
on-site or remotely.
The BDS stores these kinds of data:
Alarms - 100 records that show when a parameter went into alarm and left alarm, and
maximum alarm level. Older records in memory are overwritten with more recent events.
(Older records uploaded to a computer are not overwritten.)
Discharge - 160kb of nonvolatile memory are allocated for discharge data. Memory size and
the number of cells monitored limit the data stored: many short or a few full discharges.
Each data point requires ten bytes of memory. The discharge storage threshold is 10mv. If a
typical discharge for 192 cells was to discharge 1.65 volts per cell, and the cell voltage was to
drop to 1.96 volts when load was applied, you would calculate the memory required as:
160,000 bytes / ( ( ( (1.96-1.65) / 0.010 volts) x 10 bytes) x 192 cells) = 2.7 discharges
This worst case assumes all cells reach end voltage. Time stamped data allow a full analysis
of battery performance during the event.
Resistance - 10.6kb of nonvolatile memory are allocated for resistance data. Memory limits
the number of resistance tests stored. To calculate the number of resistance records available,
use the formula:
10,600 bytes / ( (Number of cells x 4) + 30)
For a string of 192 cells, there is enough memory for 12 records.
Historical Data - With 32kb of nonvolatile memory available, historical readings of cell
voltage, temperature, overall voltage, and current are taken at intervals set under Battery
Setup. To calculate the number of historical records available, use the formula:
32,000 bytes / ( (Number of cells x 2) + 38)
For a string of 192 cells, there is enough memory for 75 records.