Campbell Scientific AP200 CO2/H2O Atmospheric Profile System - Manual (Page 72)

Appendix B. AP200 Diagnostics
Second, because it is an average over time, it is impossible to tell which bits
are set. For example, an average of 4.0 could mean that bit 3 (numeric value =
4) is set all the time or it could mean that bit 4 (numeric value = 8) is set half
the time, etc. For this reason, diag_AP200_Avg can indicate only whether or
not there was a problem (nonzero value) or not. If diag_AP200_Avg is
nonzero, use the time series of diag_AP200 in the RawData table to diagnose
the problem.
The following sections give details on each of the diagnostic bits.
Bit 1: Battery voltage is too low
If bit 1 of diag_AP200 is set, this indicates the power source for the AP200 has
dropped below the acceptable voltage limit. This triggers the AP200 to power
down as much of the system as possible to protect the user’s battery from a
deep discharge that might damage the battery. The pump, valves, pump and
valve heaters and fans, and intake heaters will all be turned off. The IRGA is
powered directly, so it cannot be turned off. The AP200 will power up again
when the supply voltage reaches an acceptable level.
There are two system configuration variables, BATT_LOLIMIT and
BATT_DEADBAND, that determine the shut-down and turn-on voltage (see
Section 5.4.1, System Configuration Variables).
To confirm the problem, verify public variable batt_volt_LOW = True. This
variable is set to True if the battery voltage falls below the shutoff limit:
batt_volt < BATT_LOLIMIT
Note that batt_volt_LOW will remain True until the supply voltage reaches
the turn-on voltage:
batt_volt > BATT_LOLIMIT + BATT_DEADBAND
The purpose of the deadband (the gap between the shut-down voltage and the
turn-on voltage) is to protect the AP200 from repeated power cycles when the
battery voltage is very near the shut-down limit. Note that for troubleshooting
purposes, if batt_volt_LOW = True and batt_volt is in the deadband,
manually set batt_volt_LOW = False. This will let the AP200 power up.
If this does not work, measure the voltage at the AP200 power input terminals,
and compare this to batt_volt. Note that batt_volt is measured in the
datalogger which has a diode for reverse voltage protection. The actual voltage
at the input terminals will be approximately 0.3 volts higher than the value
reported by batt_volt.
The AP200 supply voltage must be 10.0 Vdc to 16.0 Vdc. See Section 4.3.2,
System Enclosure, for details on the power required, especially the extra power
required for a cold startup.
B-2