Valeport Ltd

- Model CTD - High Stability Conductivity Profiler Sensor

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The MIDAS CTD (previously known as the Model 606) is Valeport's premier CTD Profiler. High accuracy sensors (including ±0.01% pressure) and robust titanium design allow reliable operation to 6000m depth, under the harshest conditions. It also features truly synchronised sampling to ensure that all sensors are sampled at exactly the same point during a profile. Primarily for use as a self recording profiler, the MIDAS CTD also has a range of communications options for real time use, and the low power consumption and large memory also make it suitable for longer term deployments.

Sensors

The MIDAS CTD is fitted with Valeport’s high stability conductivity sensor, a high accuracy temperature compensated piezo-resistive pressure transducer, and a fast response PRT temperature sensor.

Conductivity

  • Range: 0 - 80 mS/cm
  • Resolution: 0.002mS/cm
  • Accuracy: ±0.01mS/cm

Temperature

  • Range: -5°C to +35°C
  • Resolution: 0.005°C
  • Accuracy: ±0.01°C

Pressure

  • Range: 10, 50, 100, 300 or 600bar
  • Resolution: 0.001% range
  • Accuracy: ±0.01% range

Data Acquisition
The MIDAS CTD uses the concept of distributed processing, where each sensor has its own microprocessor controlling sampling and calibration of readings. Each of these is then controlled by a central processor, which issues global commands and handles all the data. This means that all data is sampled at precisely the same instant, giving superior quality profile data.

Sampling Modes

  • Continuous: Regular output from all sensors at 1, 2, 4 or 8Hz.
  • Burst: Regular sampling pattern, where instrument takes a number of readings, then sleeps for a defined time.
  • Trip/Profile: Data is output as a chosen parameter changes by a set value, usually Pressure for profiling.
  • Conditional: Instrument sleeps until a selected parameter reaches a set value.
  • Delay: Instrument sleeps until predefined start time

Communications
The instrument will operate autonomously, with setup and data extraction performed by direct communications with PC before and after deployment. It also operates in real time, with a choice of communication protocols for a variety of cable lengths, all fitted as standard and selected by pin choice on the output connector:

Standard

  • RS232 Up to 200m cable, direct to serial port via USB adaptor
  • RS485 Up to 1000m cable, addressable half duplex comms

Options

  • FSK 2 wire power & comms up to 6000m cable (cable dependant)
  • Baud Rate: 2400 - 115200 (FSK fixed at 19200, USB 460800)
  • Protocol: 8 data bits, 1 stop bit, No parity, No flow control

Memory

The MIDAS CTD is fitted with 16Mb solid state non-volatile FLASH memory. Total capacity depends on sampling mode; continuous & burst modes have a single time stamp at the start of the file, trip mode (profiling) stores a time stamp with each reading. A single line of CTD data uses 6 bytes, and a time stamp uses 7 bytes.

  • Continuous: >2,700,000 data points
  • Profile: >1,200,000 data points (>100 profiles to 6000m).

Electrical

  • Internal: 8 x C cells, 1.5v alkaline or 3.6v lithium
  • External: 9 - 30vDC
  • Power: 0.6W (sampling), <1mW (sleeping)
  • Battery Life:
    • <100 hours operation (alkaline)
    • <250 hours operation (lithium)
  • Connector: Subconn MCBH10F

Physical

  • Materials: Titanium housing, polyurethane sensor components, stainless steel (316) cage
  • Depth Rating: 6000m (may be limited by pressure sensor)
  • Instrument Size: 88mmØ x 665mm long
  • Cage Size: 750 x 140 x 120mm
  • Weight (in cage): 11.5kg (in air), 8.5kg (in water)
  • Shipping: 100 x 18 x 49cm, 24kg

Software

  • System is supplied with DataLog Express Windows based PC software, for instrument setup, data extraction and display. DataLog Express is license free.

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