Application and Design Specifications

The initial application is to log the analog output from a Rockland Scientific MicroSquid.

MicroSquid-C

MicroSquid refers to the whole package offered by Rockland Scientific, but we are only concerned with the micro-conductivity sensor, MS-C. This is a SBE7 microconductivity probe (a very fancy pair of wires), with the associated drive and sense circuitry. For the freebird,this is essentially a black box with the following characteristics:

• power requirements: 4-32 V DC at 0.5 W
• analog signal: analog ground and analog 0-5V sensor output.
• analog signal is pre-emphasized between 10Hz and 100Hz, with an 8-pole antialias filter at 110Hz.

For estuarine deployment, we are aiming for 12-bit precision. The primary use for these data will be spectral analysis, so scale nonlinearity is less of an issue compared to noise or poor frequency response.

Deployment plan

The logger will be mounted in a pressure housing along with the battery pack. This housing will then be mounted in stainless steel CTD cage, along with the MicroSquid-C and an RBR CTD (the RBR CTD samples at 6Hz, but is typically much more stable). The MicroSquid-C is cabled to the logger for power and analog signal. The initial setup will rely on a precision real-time clock in the logger to allow synchronizing the data streams after the fact.

The CTD cage will be deployed one day at time, mostly from a deck-mounted winch. Ideally the battery pack will be sufficient to power the logger and microsquid-c for a full 16 hour day. At the start of a day, fresh batteries (ideally CR123 lithiums, same as RBR CTDs) are installed, and the pressure housing sealed. At the end of the day, the SD card is pulled out, data copied, and ready for the next day with fresh batteries.

Possible extensions

While we're not trying to design these in right now, where possible I'm trying to allow for these upgrades:

• serial cable from RBR to the freebird for synchronous data collection
• bluetooth or wifi to check status without opening the pressure housing
• piezo beeper "heartbeat" to indicate okay status without having to open the pressure housing