Campbell Scientific IRGASON Integrated CO2/H2O Open-Path Gas Analyzer and 3D Sonic Anemometer - Manual (Page 32)

IRGASON ® Integrated CO
2
/H
2
O Open-Path Gas Analyzer and 3D Sonic Anemometer
8. EC100 Outputs
The EC100 is the IRGASON electronics module that measures the sensors and
controls the system. It outputs data in one of four types: SDM, USB, RS-485,
or analog. In general, Campbell Scientific recommends that SDM be used if a
Campbell Scientific datalogger is responsible for data collection. However,
RS-485 output is recommended if cable lengths exceed 100 meters. If a PC is
being used as the collection vehicle, USB and RS-485 are suitable outputs.
Analog output may also be used; however, only CO
2
density and H
2
O density
will be output. Information regarding each output type is provided in the
following sections.
8.1 SDM Output
SDM ( Synchronous Device for Measurement) is a proprietary Campbell
Scientific communication protocol that allows synchronized measurement and
rapid communication between a Campbell Scientific datalogger and multiple
devices, including the IRGASON. Although nearly all Campbell Scientific
dataloggers support SDM, only the CR1000, CR3000, and CR5000 dataloggers
support the IRGASON.
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 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
IRGASON has a factory default SDM address of 1, but it may be changed to
any integer value between 0 and 14 (see Section 7.2, Bandwidth).
The sample rate for SDM output is determined by the inverse of the datalogger
scan interval, as set by the user in the datalogger program. Data are output
from the EC100 when a request is received from the logger, that is, 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 IRGASON. This instruction is
explained in detail under Section 10.1, EC100() Instruction.
8.2 USB or RS-485 Output
In contrast to the SDM output mode, which is prompted by a datalogger, data
can also be output from the EC100 via USB or RS-485 in an unprompted
mode. In this case, the EC100 sends out data without initiation from the
receiving device at a rate determined by the EC100. Only one unprompted
output type, USB or RS-485, may be selected at a given time. RS-485 output
is recommended if cable lengths exceed 100 meters. If a Campbell Scientific
datalogger is not being used to collect the data from the IRGASON, either
unprompted mode is recommended.
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