Campbell-scientific EC155 CO2 and H2O Closed-Path Gas Analyzer and EC1 Manuel d'utilisateur télécharger pdf (Page 35)

EC155 CO

and H

O Closed-Path Gas Analyzer

TABLE 8-1. USB and RS-485 Output Elements

Data

Element

Description Units/comments

m/s

2 Uy m/s

m/s

Sonic Temperature

°C

5 Sonic Diagnostic Flag

Concentration

µmol/mol

O Concentration

mmol/mol

8 Gas Diagnostic Flag

Air Temperature

°C

Air Pressure

kPa

11 CO

Signal Strength Nominally 0.0 to 1.0

O Signal Strength

Nominally 0.0 to 1.0

Sample Cell Pressure

Differential

kPa

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

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.

1 2 ... 30 31 32 33 34 35 36 37 38 39 40 ... 69 70

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Campbell-scientific EC155 CO2 and H2O Closed-Path Gas Analyzer and EC1 Manuel d'utilisateur Page 35

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