Campbell Scientific AP200 CO2/H2O Atmospheric Profile System - Manual (Page 29)

AP200 CO
2
/H
2
O Atmospheric Profile System
FIGURE 4-22. Pump module of AP200 system
The AP200 pump module pulls air through the system and exhausts it through
the Exhaust fitting on the bottom of the system enclosure. It uses a small
double-head diaphragm pump with a brushless DC motor. This pump includes
a speed control input and a tachometer to measure the actual pumping speed. It
is mounted in an insulated, temperature-controlled box inside the AP200
system enclosure. The following sections describe the monitored pump
operating parameters.
Pump Inlet Pressure: The measured inlet pressure of the pump is reported in
public variable pump_press. The AP200 sets the value of public variable
pump_control to a value between 0 (off) and 1 (full speed) to adjust the
pump’s speed as needed to match the measured pressure to the setpoint
pressure PUMP_P_SETPT. PUMP_P_SETPT is a system configuration
variable (see Section 5.4.1, System Configuration Variables). This pressure
setting affects the power required for the pump (lower pressure requires more
power), the possibility of water condensing in the tubing (lower pressure helps
to prevent condensation), and the flow rate (lower pressure will increase the
flow rate). The pump can achieve a maximum of approximately 60 kPa
pressure drop from ambient pressure at zero flow. The recommended setting
for the pump is 35 kPa below ambient pressure.
The pump module includes two buffer volumes to dampen the pressure
fluctuations from the pump. The sample flow from the IRGA flows through
these volumes in series on the way to the pump. The bypass flow (from non-
selected inlets) connects directly to the pump.
Pump Speed: The measured pumping speed is reported in public variable
pump_speed. This is the rotational speed of the pump, given in Hz. The
pumping speed will typically be 25 Hz to 40 Hz. The actual value is not
critical, however, as long as the pressure can be maintained at the setpoint.
17