Campbell IRGASON, Руководство по эксплуатации продукта

Страница: 34 / 91

In most situations, a PC begins by reading the ASCII data and extracting the last four ASCII
characters and casting them as Long data type. The signature is then calculated on the science
data sent from the IRGASON, starting with CO
2
and ending on the counter. All the characters
after the counter are not part of the signature. Once the signature is computed using the
following algorithm, it is compared to the transmitted signature. If signatures do not match, the
data should be disregarded.
Following is an example implementation of Campbell Scientific’s signature algorithm in the
programming language C. To generate the signature of an output array of bytes, the “seed”
needs to be initialized to 0xaaaa and a pointer passed to the first byte of the output array. The
number of bytes in the output array should be entered in as the “swath”. The returned value is
the computed signature.
//signature(), signature algorithm.
// Standard signature is initialized with a seed of 0xaaaa.
// Returns signature.
unsigned short signature( unsigned char* buf, int swath,
unsigned short seed ) {
unsigned char msb, lsb;
unsigned char b;
int i;
msb = seed >> 8;
lsb = seed;
for( i = 0; i < swath; i++ ) {
b = (lsb << 1) + msb + *buf++;
if( lsb & 0x80 ) b++;
msb = lsb;
lsb = b;
}
return (unsigned short)((msb << 8) + lsb);
}
8.3 Analog outputs
If analog output is enabled, the EC100 will output two analog signals that correspond to CO
2
density and H
2
O density. These signals range from 0 to 5000 mV. Table 8-2 (p. 31) gives the
multipliers and offsets for the analog outputs. Note that the analog outputs contain no sonic
data.
IRGASON® Integrated CO
2
/H
2
O Open-Path Gas Analyzer and 3D Sonic Anemometer 30