Campbell Scientific EC150 CO2 and H2O Open-Path Gas Analyzer and EC100 Electronics with Optional CSAT3A 3D Sonic Anemometer - Manual (Page 66)

Appendix C. Alternate EC100 Outputs
TABLE C-1. USB and RS-485 Output Elements
Data
Element Description
Units or comments
5 Sonic Diagnostic Flag
6 CO
2
Density mg·m -3
7 H
2
O Density g·m -3
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
Pressure Differential (used for EC155
only, disregard for EC150)
kPa
14 Counter Arbitrary
15 Signature
Arbitrary in
hexadecimal
FIGURE C-1. USB data output in terminal mode
The final data element in each row or output array is the signature which can
be used to identify transmission errors similar to a Cyclic-Redundancy-Check
(CRC). The signature is a four character hexadecimal value that is a function
of the specific sequence and number of bytes in the output array. To check for
transmission errors, the recording device (such as a 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
If signatures do not match, the data should be disregarded.
The block of code below 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.
C-2