Campbell Scientific EC150 CO2 and H2O Open-Path Gas Analyzer and EC100 Electronics with Optional CSAT3A 3D Sonic Anemometer - Manual (Page 15)

EC150 CO
2
/H
2
O Open-Path Gas Analyzer
4.6.2.1 SDM Output
To use SDM data output, connect an SDM communications cable from the
EC100 (see Section 6.3, Wiring and Connections) to a CR1000, CR3000, or
CR5000 datalogger. On CR1000 dataloggers, the SDM protocol uses ports C1,
C2, and C3. These are multipurpose control ports that are SDM-activated
when an SDM instruction is used in the datalogger’s program. On CR3000 and
CR5000 dataloggers, the SDM protocol uses SDM-dedicated ports SDM-C1,
SDM-C2, and SDM-C3.
Each SDM device on the SDM bus must have a unique address. The EC150
has a factory default SDM address of 1, but may be changed to any integer
value between 0 and 14 (see Appendix A.2.1, SDM Address).
The sample rate for SDM output is determined by the datalogger program.
Data are output from the EC100 when a request is received from the datalogger
(for example, a prompted output mode). The number of data values sent from
the EC100 to the datalogger is also set by the user in the datalogger program.
CRBasic, the programming language used by Campbell Scientific dataloggers,
uses the EC100() instruction to get data from an EC150. This instruction is
explained in greater detail under Appendix A, EC150 Settings, and in
Appendix A.5, EC100 Configure() Instruction.
4.7 Automatic Heater Control
An advantage of the EC150’s low power consumption (5W) is that the
instrument remains at a temperature very close to ambient air temperature,
which is an important feature for eddy-covariance measurements. Under some
environmental conditions, however, the analyzer can become colder than
ambient air temperature which may increase the likelihood of frost or
condensation building on the optical windows. This will affect signal strength.
The EC150 design includes internal heaters located at the optical windows,
which aid in minimizing data loss during these specific environmental
conditions.
An automatic heater control algorithm can be activated from either Device
Configuration or ECMon by putting in a value of −2, or deactivated by putting
in a value of −1. i The algorithm uses the internal heaters to maintain a
temperature that is a couple of degrees above the ambient dewpoint (or frost
point) to prevent condensation and icing from forming on the surface of the
optical windows.
The heater control will be disabled under any of the following conditions:
• Temperature of the detector housing is outside the −35°C to +55°C
range
• Temperature of the source housing exceeds 40°C
• Ambient temperature is outside the −35°C to +55°C range
• The supply voltage is below 10 V
i Automatic heater control is available in EC100 OS version 4.07 or greater and is turned on by
default starting with the OPEC program version 3.2.
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