Campbell Scientific CPEC200 Closed-Path Eddy-Covariance System User Manual

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CPEC200 Closed-Path Eddy-Covariance System

PUMP_SETPT:

Variable

PUMP_SETPT determines the volumetric flow rate at which the

pump will draw the air sample through the EC155 sample cell.

PUMP_SETPT must be 3 to 9. The default setting is 7.0 LPM. In tall tower

applications where decreased frequency response is acceptable, lowering the

flow rate may be desirable as it will prolong the life of the intake filter. This

may be particularly applicable if the site is dusty or if accessing instruments on

the tower is difficult. Decreasing the flow by a factor of two will generally

lead to a four-fold increase in filter lifetime.

CAL_INTERVAL:

This variable determines how often (given in minutes) the calibration

(zero/span) sequence will be run. It is ignored if

CHECK_ZERO = False.

The minimum time is the output interval (30 min). The maximum time is

1,440 min, or once per day. The default is 1,440.

CAL_TIMEOFFSET:

This variable determines when the calibration (zero/span) sequence is started

within the

CAL_INTERVAL time. If CAL_TIMEOFFSET = 0, the

calibration sequence will start at the start of the

CAL_INTERVAL. Setting

this variable to a non-zero value will delay the start of the zero/span sequence

by the set number of minutes.

CAL_TIMEOFFSET may be set to any value

from zero to

CAL_INTERVAL. The default is 59, which will start the

zero/span sequence 59 minutes past midnight. This avoids starting the

zero/span sequence at midnight, when the datalogger has the extra processing

tasks associated with closing and opening files for the

ts_data table. It starts

the sequence one minute before the end of an averaging period. The sequence

is generally longer than one minute, so the EC samples that are lost to the

zero/span sequence are split between two consecutive flux output intervals.

ZERO_TIME:

Determines the time (given in seconds) for the zero gas to flow while checking

the zero.

ZERO_TIME must be 20 to 300. The default is 60, which should be

adequate for low measurement heights. For taller towers, increase the time as

needed to allow the EC155 response to equilibrate after the zero air begins to

flow.

SPAN_TIME:

Determines the time (given in seconds) for the CO

span gas to flow. Time for

zero and CO

span may need to be different to allow the H

O to fully

equilibrate during the zero. If the scrub module is used for the zero air, the

flow rate will be different for zero and CO

span. This is another reason to set

the zero and span times differently.

SPAN_TIME must be 20 to 300. The

default is 30, which should be adequate for low measurement heights. For

taller towers, increase the time as needed to allow the EC155 response to

equilibrate after the CO

span gas begins to flow.