User manual

NOTE
During a profile, the firmware periodically sends a data request to the CTD while the CTD is
logging internally. The CTD responds with the most recent scan of data which is parsed to
extract the pressure used in the stop check internal algorithm.
Infrequent checks (30 to 60 second intervals) save a small amount of power and are
appropriate for relatively long profiles (>500m). Unfortunately, a 30-60 second stop check
interval also permits the MMP to overshoot the pressure stop and push against the physical stop
until the next stop check. More frequent checks (5 to 15 second intervals), use more power but
also reduce overshoot. Frequent checks are appropriate for relatively short profiles (< 500m).
Motor currents above 1500 mA indicate a catastrophic circuit failure and result in
immediate termination of profiler motion. High motor currents initiate the ramming behavior,
similar to the repetitive attempts to pass an obstacle. High motor currents do not end the
deployment.
The MMP uses a threshold of 7.5 V to detect battery exhaustion and terminate the
deployment. The output voltage of the main lithium battery is nominally 10.8 V until ~90% of
the available energy in the battery has been used. The voltage then drops rapidly to ~7.8 V and
remains at that level while most of the remaining available energy is used. As the battery nears
complete exhaustion (99+% of the available energy extracted), the voltage falls rapidly to zero
unless the current drain is drastically reduced. To avoid a premature or erroneous termination of
the deployment, the battery voltage is averaged over five clean measurements obtained during
sequential stop checks. Allowed range: 1 second to 60 seconds in 1 second increments.
The stop check “algorithm” is:
• Firmware always checks:
• Motor current below 1500 mA
• Elapsed time less than profile time limit
• Battery voltage above 7.5 V
• Firmware checks after velocity ramp:
• Pressure
• Pressure rate
7-56