The HL4 is Hydrolab’s next-generation sonde and a replacement for the DS and MS series products.

  • SDI-12, RS-232, and RS-485 communication options
  • Self-monitoring system reports the status of the instrument, flags the data, and shows the user where the problem is with assistance on how to solve the issue
  • User-scheduled calibration and maintenance intervals indicate when they are due
  • Guided and semi-automated calibration routines lead the user through the calibration process
  • Calibration results are stored with date and time, calibration type, user identification, and user notes
  • Check Calibration process allows the user to verify calibration and store the results
  • Calibration reports contain information about previous calibrations and calibration checks
  • Sensor status is saved with every line of data and is contained in the log file
  • Dedicated communications modules allow easy integration with data loggers and telemetry systems

Sensors available:

  • Conductivity
  • LDO (luminescent dissolved oxygen)
  • Temperature
  • pH
  • Depth/Vented Level
  • Turbidity
  • ORP (Oxygen Redox Potential)

Technical Specifications


External 6-30 VDC (12 VDC nominal) applied to the communications module,
12 VDC: 250 mW average, 19 W peak
Internal (Optional) Internal alkaline D-cell battery, non-rechargeable.
Sleep mode at 12 V 20 mA
Communications Hydrolab communications modules: USB, SDI-12, RS232, RS485, or TTY
Memory 4 GB of internal memory; 1 second interval minimum


Sonde depth rating 200 m (656 ft)
Maximum Deployment Cable 200 m (656 ft)
Diameter without bumpers 4.4 cm (1.75 in.)
Diameter with bumpers 5.3 cm (2.1 in.)
Weight with internal battery pack (IBP) and storage/calibration cup 2.2 kg (5 lb)
Length - no IBP, standard sensor guard 51.4 cm (20.25 in.)
Length - no IBP, extended sensor guard 66.4 cm (26.125 in.)
Length - IBP and standard sensor guard 62.2cm (24.5 in.)
Length - IBP and extended sensor guard 77.8 cm (30.625 in.)

Environmental conditions

Operating temperature -5 °C to 50 °C (23 °F to 122 °F), non-freezing
Storage temperature 1 °C to 50 °C (34 °F to 122 °F)


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