User manual

NOTE
During a profile, while the CTD is logging autonomously, the TT8v2 periodically sends a
carriage return to the CTD over the serial communications link. The CTD responds with the
most recent scan of data. The firmware parses the response string to extract the pressure and
uses that information to determine when a profile is complete.
Infrequent checks (30 to 60 second intervals) save a small amount of power because the
TT8v2 spends a larger portion of the profile in low power sleep. Infrequent checks are
appropriate for relatively long profiles (>500m) Infrequent checks also permit the MMP to
overshoot the pressure stops and push against the physical stops while the TT8v2 sleeps, waiting
for 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).
Detection of 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 are not
grounds for deployment termination.
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 summarized next.
• System always checks:
• Motor current below 1500 mA
• Elapsed time less than profile time limit
• Battery voltage above 7.5 V
• System checks after velocity ramp:
• Pressure
• Pressure rate
G-52