Campbell Scientific EC155 CO2 and H2O Closed-Path Gas Analyzer and EC100 Electronics with Optional CSAT3A 3D Sonic Anemometer - Manual (Page 36)

EC155 CO
2
and H
2
O Closed-Path Gas Analyzer
The following block of code 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 +5
Volts. TABLE 8-2 below gives the multipliers and offsets for the analog
outputs.
TABLE 8-2. Multipliers and Offsets for Analog Outputs
Mixing Ratio
(µmol mol -1 )
Voltage Output Multiplier
(µmol mol -1 V -1 )
Offset
(µmol mol -1 )
CO
2
211.27 -56.34
H
2
O 11.31 -3.04
9. Maintenance
There are five basic types of maintenance for the EC155/EC100: intake filter
replacement (if EC155 was ordered with an intake), analyzer window cleaning,
zero and spanning, replacing analyzer desiccant/scrubber bottles, and factory
recalibration.
9.1 Routine Maintenance
The following items should be examined periodically:
• Check the humidity indicator card in the EC100 enclosure. If the highest
dot has turned pink, replace or recharge the desiccant bags. Replacement
desiccant bags may be purchased (pn 6714), or old ones may be recharged
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