Campbell Scientific AP200 CO2/H2O Atmospheric Profile System - Manual (Page 28)

AP200 CO
2
/H
2
O Atmospheric Profile System
The valve manifold has eleven inlets (eight for air samples and three for
zero/span) and two outlets (sample and bypass). Each air sample inlet has a
three-way solenoid valve that connects it to one of the two outlets. This valve
connects its corresponding inlet to the bypass outlet when it is off and to the
sample outlet when it is energized. The sample outlet connects to the IRGA
and the bypass outlet connects directly to the pump. Therefore, the sample
inlets will have a continuous flow, regardless of which inlet is sampled by the
IRGA. This continuous flow stores an air-sample history in the intake
assembly mixing volumes, keeps the mixing volumes and sample tubes at low
pressure to prevent condensation, and minimizes flow and pressure transients
caused by valve switching.
The zero/span inlets are not bypassed, thereby allowing flow only when they
are selected. These inlets have flow restriction tubes connecting the bulkhead
fittings to the valve manifold to set the flow. These tubes have the same outer
diameter (0.062 in) as the ones for the air sample inlets, but they have a smaller
inner diameter (0.015 in, compared to 0.040 in). This provides a flow
restriction similar to the orifices in the AP200 intake assemblies. The flow for
the zero and CO
2
span cylinders is affected by the pressure regulator setting.
The valve manifold has a mass flow sensor on the sample outlet. This sensor’s
measurements are reported in public variable sample_flow.
The valve manifold temperature is reported in public variable valve_tmpr. The
operating range of the valves is 4°C to 49°C. If the valve temperature is outside
this range, the AP200 will disable the valves and pump.
The valve module has a heater (8 W) that turns on if the valve temperature falls
below 5°C. If the AP200 is started at cold temperature it may take up to 20
minutes to warm the valve module (from –30°C to +4°C). When it reaches 5°C
the heater will cycle on/off as needed to maintain this temperature. The fraction
of time the valve heater is on is reported in the output tables ( IntAvg, CalAvg,
and SiteAvg) as valve_heat_Avg. This will typically increase from zero at 0°C
ambient temperature to 0.5 (4 W average power) at –30°C.
The valve module has a fan (0.7 W) that turns on if the valve temperature rises
above 45°C. The fan will stay on until the valve temperature falls below 43°C.
The fraction of time the valve fan is on is reported in the output tables ( IntAvg,
CalAvg, and SiteAvg) as valve_fan_Avg. This will typically increase from
zero at 35°C ambient temperature to 1.0 (0.7 W average power) at 45°C.
4.2.3 Pump Module
The AP200 pump module is mounted on the left side of the AP200 system
enclosure as shown in FIGURE 4-22.
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