Campbell Scientific CPEC200 Closed-Path Eddy-Covariance System - Manual (Page 26)

CPEC200 Closed-Path Eddy-Covariance System
The CPEC200 valve module includes a heater and a fan to keep the valves
within their operating range of 0°C to 60°C. The valve heater turns on/off at
2°C. The valve fan turns on at 50°C and stays on until the valve temperature
drops to 48°C. To conserve power, temperature control is active just prior to
and during the time when valves are in use. If the valves cannot be maintained
within the temperature range, the valves are disabled. The valve module
temperature control can be manually activated so that manual zero/span can be
performed by the station operator on site or remotely. If starting from the
minimum ambient temperature (–30°C), the valves may take as much as 15
min to warm up to the operating range of 0°C to 60°C.
4.2.4 Pump Module
The CPEC200 pump module pulls air through the system and exhausts it
through the Exhaust fitting on the bottom of the 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 located inside the
weather-tight fiberglass enclosure. The pump module includes a large filter
cartridge to dampen the pressure fluctuations from the pump and to protect the
pump from particulates or debris.
If the pump fails, the replacement pump is available as pn 26402 (see Section
4.1.5, Replacement Parts). See Appendix H, CPEC200 Pump Replacement,
for instructions on replacing the pump. The filter cartridge in the pump module
is unlikely to clog over the lifetime of the CPEC200 system.
The following sections describe operating parameters of the pump.
Pump Speed: The pump tachometer is measured, converted to volumetric
flow rate, and reported in public variable pump_flow. The CPEC200 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 pump_flow to the
setpoint flow PUMP_SETPT. PUMP_SETPT is a system configuration
variable (see Section 5.4.1, System Configuration Variables).
Pump Inlet Pressure: The measured inlet pressure of the pump is reported in
public variable pump_press. This pressure will normally be slightly lower (~1
kPa) than the EC155 sample cell pressure due to the pressure drop in the pump
tube.
Pump Temperature: The temperature of the pump module is reported in
public variable pump_tmpr. The operating range of the pump is 0°C to 55°C.
If the pump temperature is outside this range, the CPEC200 will disable the
pump. The pump module has a heater (drawing 8 W while operational) that
turns on if the pump temperature falls below 2°C. If the CPEC200 is started at
cold temperature, it may take up to 50 minutes to warm the pump module
(from –30°C to 0°C). When it reaches 2°C the heater will cycle on/off as
needed to maintain this temperature.
The pump module has a fan (drawing 0.7 W while operational) that turns on if
the pump temperature rises above 50°C. The fan will stay on until the pump
temperature falls below 45°C.
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