Raw Data Capture
Command
Default
Name
Usage
Parameter
“set S 0" will save the current settings to the on-board EEPROM.
S
NA
EEPROM Settings
“set S 1" will retrieve the settings from the EEPROM.
“get S” is not a valid command.
“get V” will return the firmware version information.
V
NA
Firmware Version
“set V” is not a valid command.
“get W” will return <number> sequential raw ADC samples. If
<number> exceeds 2048, then 2048 samples will be returned. Note
that this is the only get command which accepts an additional
W
NA
Capture ADC Sample Data
parameter.
The W command also returns the stored sample rate.
“set W” is not a valid command.
“set X 1" will enable the automatic clearing of detected arcs (a
detected arc will be cleared approximately. 4sec after detection
without any command issued).
“set X 0" will disable the automatic clearing. When auto-clear is
X
1 (On)
Arc Detect Automatic Clearing
disabled, a “set A” is the only way to clear a detected arc.
“get X” will return the string ‘Detected Arcs Auto-Cleared” or
“Detected Arcs not Auto-Cleared” based on the current setting. The
default setting is automatic clearing of detected arcs.
“set Z 1” enables self test.
Z
0 (Off)
Self Test
”set Z 0” disables this function.
get Z” returns self test status “INACTIVE” or “ACTIVE”.
10
Raw Data Capture
For most efficient capturing of raw ADC codes, turn off the notifications and disable arc detection, by
sending the following instructions:
set N 0
set R 0
Once these commands are issued, you should configure HyperTerminal to save the raw data to a file by
selecting Transfer>Capture Text, and then set the filename to the conditions that are on the line (e.g.
inverter_A_10panels_no_arc.txt), when click ‘Start’. You can then capture the data with:
get W 2000
Once the text transfer is complete (after approximately 2 seconds), close the HyperTerminal file by
selecting Transfer>Capture Text>Stop. You can then repeat the file open, get W, and file close process
until all desired conditions are saved in a text file.
11
Theory of Operation
Arcing present in a PV system creates random noise current in the cabling used for the PV string. The
current noise of the arc itself has a Gaussian distribution with a spectrum extending to several MHz.
Because of the geometry of the cabling in a typical PV system, the noise current density above 200 kHz
varies significantly with frequency. The inverters used in PV systems usually use switch mode controllers
to regulate the incoming DC voltage. These switching regulators usually operate in the kHz range,
generally below 50kHz, and introduce an AC interfering signal on the PV string wiring at the switching
frequency. For these reasons, noise in the band of frequencies between 40 kHz and 100 kHz was
selected for arc detection. The point in the PV string in which the arc detection system is used may be at a
potential of as high as 1000 VDC and the current in the system may have a DC component as high as 15
Amps DC. To isolate the high DC voltage and current from the arc monitoring circuit, an isolation
transformer is used. A reasonably sized transformer meeting these requirements has relatively low
magnetization inductance. Because of this, the noise signal at the secondary of the transformer is
relatively low.
6
AN-2154 RD-195 DC Arc Detection Evaluation Board
SNOA564F – June 2011 – Revised December 2012
Copyright © 2011–2012, Texas Instruments Incorporated
