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Reference Sheet
Configuration options & accessories
DESCRIPTION
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The SBE 37-IM MicroCAT is a high-accuracy conductivity and temperature sensor/recorder (pressure optional) with internal battery, non-volatile memory, and built-in Inductive Modem.
The inductive modem provides reliable, low-cost, real-time data transmission for up to 100 instruments — all MicroCATs or a mix of MicroCATs and other IM instruments — using plastic-coated wire rope (typically 3 x 19 galvanized steel) as both the transmission line and mooring tension member. IM instruments clamp anywhere along the rugged mooring wire. Expensive and potentially unreliable multi-conductor electrical cables with fixed position underwater connectors are not required. IM moorings are easily reconfigured for changing deployments (positions can be changed or instruments added or removed), by sliding and re-clamping sensors on the cable. IM systems are much less expensive and more power-efficient than acoustic modems, and offer reliable communication over greater distances.
In a typical real-time surface mooring, a Surface Inductive Modem (SIM) housed in the buoy communicates with underwater IM instruments and is interfaced to a computer or data logger via an RS-232 serial port. The computer or data logger (not supplied by Sea-Bird) is programmed to poll each IM instrument on the mooring for its data, assemble all the data into files, and send the files to a telemetry transmitter (satellite link, cell phone, RF modem, etc.). The MicroCAT simultaneously saves it data in memory for upload after recovery, providing a backup against lost data in the event real-time telemetry is interrupted.
SENSORS AND INTERFACE ELECTRONICS
The MicroCAT retains the temperature and conductivity sensors used in our time-proven SEACAT and SEACATplus products. Calibration coefficients are stored in EEPROM, allowing the MicroCAT to transmit data in engineering units. Sea-Bird’s unique internal-field conductivity cell permits the use of expendable anti-foulant devices. The aged and pressure-protected thermistor has a long history of exceptional accuracy and stability.
Temperature is acquired by applying an AC excitation to a hermetically sealed VISHAY reference resistor and an ultra-stable aged thermistor (drift rate typically less than 0.002 °C per year). The ratio of thermistor resistance to reference resistance is determined by a 24-bit A/D converter; this A/D also processes the pressure sensor signal. Conductivity is acquired using an ultra-precision Wien-Bridge oscillator.
The optional Druck pressure sensor has a superior design that is entirely different from conventional ‘silicon’ types in which the deflection of a metallic diaphragm is detected by epoxy-bonded silicon strain gauges. The Druck sensor employs a micro-machined silicon diaphragm into which the strain elements are implanted using semiconductor fabrication techniques. Unlike metal diaphragms, silicon’s crystal structure is perfectly elastic, so the sensor is essentially free of pressure hysteresis. Compensation of the temperature influence on pressure offset and scale is performed by the MicroCAT’s CPU.
COMMUNICATIONS AND INTERFACING
Both ends of the jacketed (insulated) wire rope connecting the buoy to its anchor are grounded to seawater via metal connection terminals (eyes) swaged to its steel core, completing a conductive loop through the wire rope and water. An Inductive Cable Coupler (ICC) serves as a coupling transformer similar to the one built into the MicroCAT, but clamped to the mooring wire just under the buoy, and connects to the SIM (SIM and ICC available separately). Commands and data are transmitted half-duplex between the SIM and MicroCAT using DPSK (differential-phase-shift-keyed) telemetry, providing a high degree of immunity from fish bite or other cable degradation and a maximum transmission distance of 8000 meters between the SIM and an underwater IM instrument.
Upon receipt of a wake-up command, the SIM sends a tone for 2 seconds, waking all IMs on the cable. Each IM instrument has a programmable address (0 - 99). A MicroCAT replies only to a command containing its individual ID. After replying, it returns to listening, waiting for commands. A global power-off command returns all IM instruments to standby (sleep) state. The MicroCAT automatically returns to sleep state if there is no line activity for 2 minutes.
Lab diagnostics, setup, and data extraction may be performed by simply looping any insulated wire through the inductive core and connecting the wire ends to the SIM. Alternatively, data extraction can be done via the internal RS-232 connector; binary upload capability in this mode provides fast upload of large data sets.
OPERATING MODES
User-selectable operating modes include:
SOFTWARE
The MicroCAT is supplied with a powerful Windows 2000/XP software package, SEASOFT© V2, which includes:
DATA STORAGE AND BATTERY ENDURANCE
Temperature and conductivity are stored 6 bytes/sample, time 4 bytes/sample, and optional pressure 5 bytes/sample; memory capacity is in excess of 530,000 samples. The MicroCAT is powered by a 10.6 Amp-hour (nominal) battery pack consisting of twelve AA lithium batteries (Saft LS14500) which, when removed from the MicroCAT, can be shipped via commercial aircraft. The pack provides sufficient internal battery capacity for more than 300,000 samples for a typical sampling scheme.
SPECIFICATIONS
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Measurement Range |
Initial Accuracy |
Typical Stability |
Resolution | |
| Conductivity |
0
to 7 S/m (0 to 70 mS/cm) |
0.0003 S/m (0.003 mS/cm) |
0.0003 S/m (0.003 mS/cm) per month |
0.00001 S/m (0.0001 mS/cm) |
|
Temperature (°C) |
-5 to 35 | 0.002 | 0.0002 per month | 0.0001 |
| Optional Pressure |
20 / 100 / 350 /
600 /
1000 / 2000 / 3500 / 7000 m (Expressed in meters of deployment depth capability) |
0.1% of full scale range | 0.05% of full scale range per year | 0.002% of full scale range |
Dimensions: in millimeters (inches)
Clock Accuracy: 5 seconds/month
Power Supply: 10.6 Amp-hour (nominal) battery pack
Quiescent Current: 120 microAmps
Communications Current: 2.5 milliAmps
Communications Time: 0.5 seconds/sample
Acquisition Current: 13 milliAmps
Acquisition Time: 1.8 - 2.6 seconds/sample, dependent on sampling mode and inclusion of pressure sensor
Housing, Depth Rating, and Weight (with standard mooring guide & clamp, without pressure sensor):
| Housing Material | Depth Rating | Weight | |
| Standard | Titanium | 7000 m (23,000 feet) |
4.0 kg (8.8 lbs) in
air 2.4 kg (5.3 lbs) in water |
| Optional | Plastic | 250 m (820 ft) |
2.9 kg (6.4 lbs) in
air 1.3 kg (2.9 lbs) in water |
ADDITIONAL INFORMATION / LINKS:
Documentation -- manual, photos, technical papers, application notes, etc.
Sales Information -- options, accessories, cables, mount kits, spares, etc.
Software -- components of Seasoft V2
Links to Other Instruments of Interest
Specifications are subject to change without notice.
Sea-Bird Home Phone: (+1) 425-643-9866 Fax: (+1) 425-643-9954 E-mail: seabird@seabird.com
