Campbell Scientific EC155 CO2 and H2O Closed-Path Gas Analyzer and EC100 Electronics with Optional CSAT3A 3D Sonic Anemometer - Manual (Page 35)

EC155 CO
2
and H
2
O Closed-Path Gas Analyzer
TABLE 8-1. USB and RS-485 Output Elements
Data
Element
Description Units/comments
1 Ux m/s
2 Uy m/s
3 Uz m/s
4 Sonic Temperature °C
5 Sonic Diagnostic Flag
6 CO
2
Concentration µmol/mol
7 H
2
O Concentration mmol/mol
8 Gas Diagnostic Flag
9 Air Temperature °C
10 Air Pressure kPa
11 CO
2
Signal Strength Nominally 0.0 to 1.0
12 H
2
O Signal Strength Nominally 0.0 to 1.0
13
Sample Cell Pressure
Differential
kPa
14 Counter Arbitrary
15 Signature
Arbitrary in
hexadecimal
FIGURE 8-1. An example of USB data output in terminal mode
The final data element in each row or output array is the signature, a four
character hexadecimal value that is a function of the specific sequence and
number of bytes in the output array. The recording device (i.e., PC or
datalogger) calculates its own signature using each transmitted byte until
encountering the transmitted signature. The computed signature and the
transmitted signature are compared. If they match, the data were received
correctly. This is very similar to a Cyclic-Redundancy-Check (CRC).
In most situations, a PC begins by reading in the ASCII data and extracting the
last four ASCII characters, casting them as Long data type. The signature is
then calculated on the science data sent from the EC155, 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 algorithm below, it is
compared to the transmitted signature. If signatures do not match, the data
should be disregarded.
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