Consider adding a new parameter:
@Configurable("Period")
public Period selectedPeriod = Period.TEN_SECS;
And changing the onBar method content to the following:
if (instrument.equals(selectedInstrument) && period.equals(selectedPeriod)) {
try {
out.append( sdf2.format(askBar.getTime()) + ";" + ((askBar.getClose() + bidBar.getClose() )/2) + "\n");
} catch (IOException e) {
writeMessage("File write error " );
e.printStackTrace();
}
}