Setting up and using the ISUS with Seabird CTD

1). Connect the ISUS Analog Out port to a 6-pin CTD port – we use voltage channel 6 on a universal Y-cable, allowing pH to occupy channel 7.  Map that port in Seasave as user-polynomial; under the user-polynomial, enter: A0 = - 7.1168, A1 = 27.155. 
These are linear regression coefficients from an earlier CalCOFI (1501NH).

2). Connect the battery cable to the ISUS fifteen minutes prior to deployment to "warm-up". This improves data quality & stability.

3). SIO-CalCOFI uses a 10m charging cable strung from an AC adapter in the wetlab to the battery mounted on the CTD-rosette. Between casts, the battery is left mounted on the rosette and charged. This method has improved the reliability of the ISUS to have adequate power for the full cast, provided the battery has been charged between deployments. Occasionally, the CTD operator forgets to unplug the ISUS and it logs deck data until discovered - usually next station, draining the battery & filling the ISUS internal memory.
The original method was swapping batteries every three 500m cast then charging inside the ship. The Wetlabs 12v lead-acid batteries usually lasted ~3.5 hours before requiring removal and charging. Charging takes 12-15hrs so three primary batteries were rotated. 
Regardless of charging method, be sure to unstopper the battery's vent plug to allow hydrogen emissions.  Re-stopper, greasing lightly if necessary, before mounting the fresh battery on rosette. When charging on the rosette, protect from seawater intrusion by keeping the vent-plug closed but vent the battery before deployment.

4). Remove the ISUS on casts deeper than 1000m. The 512kb memory allows storage of ~75 casts without the need to download data and purge the memory. Data are downloaded by connecting the ISUS to a Windows laptop’s serial port. If the ISUS memory is full, the sensor will still work but the sensor data profile will "stair-step" significantly.