EC155 CO
2
and H
2
O Closed-Path Gas Analyzer
55
10.3.1 ConfigCmd 11 Zero-and-Span Control
To perform zeroing of CO
2
and H
2
O,
ConfigCmd 11
is set to
1
. After the
EC155 completes the zero, it will write the value to
–1
. The datalogger can poll
this value or simply wait for a period of time to allow the zeroing to complete.
To perform CO
2
span, the CO
2
Span Concentration setting (
ConfigCmd 12
)
must be written to the proper value in ppm CO
2
prior to setting the Span/Zero
Control setting (
ConfigCmd 11
) to
2
. After the CO
2
span is completed, the
value of the Span/Zero Control setting will change to
–2
. H
2
O span is similar to
CO
2
. First the H
2
O dewpoint value (
ConfigCmd 13
) must be written to the
desired value. Then the Span/Zero Control setting is set to
3
. After the EC155
completes the span, the span control setting is written as
–3
.
ConfigCmd’s 14
through
17
automatically store the results of the zero-and-span procedure. Each
result is a coefficient used in the gas analyzer’s algorithms for calculating gas
concentrations.
10.3.2 ConfigCmd 18 Heater Voltage
Normally the
EC100Configure()
instruction is run in the datalogger’s
processing task. Skipped scans can occur when the
EC100Configure()
instruction executes. When changing operational parameters, these skipped
scans are acceptable. However, it may not be acceptable when changing the
heater voltage.
ConfigCmd 218
allows the
EC100Configure()
instruction to
operate in the SDM task, thus avoiding skipped scans. When using
ConfigCmd
218
, the command must be a constant and the instruction cannot be placed in a
conditional statement.
This setting gives the voltage applied to the intake heater. It can be set to
–1
to
disable the heater, or set it to any voltage between 0 and 4.0 V. The heater
prevents condensation in the intake tube.
The resistance of the heater in the intake assembly is 20 ohms, so the heater
power will be given by:
20
2
V
P
H
=
The maximum power (at 4.0 V) is 0.8 W. The heater may be operated
continuously at full power, over the full range of operating temperatures. If
ambient conditions are dry enough to prevent condensation without heating the
intake, the power may be turned down to conserve power. Note that the
CPEC200 system has a default to power the intake heater at its maximum
voltage to prevent condensation.
Содержание EC155
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