HL4 Hydrolab Multiparameter Water Quality Sonde
Next Generation technology
Self-monitoring system reports status of the sonde
weather applications supported water applications supported energy applications supported gas flux & turbulence applications supported infrastructure applications supported soil applications supported


The Hydrolab HL4 is the next generation multiparameter water quality sonde from OTT Hydromet. Its reliability, ease-of-use, and metadata produce water quality data you can trust.

Know the sonde is working correctly and troubleshoot quickly with the self-monitoring system that reports the status of the sonde, shows the user where potential problems are, and gives assistance on how to solve issues. Calibration is made easier with streamlined calibration tasks with user-scheduled calibration intervals and a check calibration procedure that can be used to avoid a complete calibration. Produce valid, scientifically defensible conclusions with sensor status that is saved with every line of data and calibration reports that store information about previous calibrations.

HL4 Applications

Water quality measurement in:

  • Freshwater rivers and streams, lakes and reservoirs, and groundwater wells
  • Salt or brackish water bays, estuaries, and near-coastal areas
  • Attended monitoring, continuous unattended and real-time monitoring
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Benefits and Features

  • 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
  • Guided and semi-automated calibration routines lead the user through the calibration process
  • User-scheduled calibration and maintenance intervals indicate when they are due
  • Dedicated communications modules allow easy integration with data loggers and telemetry systems
  • Compatible with the Surveyor HL – a fully IP67 handheld designed for field use with a full-color screen that is visible in direct sunlight
  • Calibration reports 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



  • Diameter: 4.44 cm (1.75 in.) without rubber bumpers
  • Length: 51.43 cm (20.25 in.) to 77.787 cm (30.625 in.)
  • Weight: 2.2 kg (5 lb) with internal battery pack and storage/calibration cup
  • Depth rating: 200 meters (656 ft) Deployment cable or mooring cap must be installed. Some sensors cannot be used at 200 m (656 ft).

Surveyor HL Handheld

  • Graphical display: Color, LCD 3.5" QVGA
  • Power supply: Lithium-ion rechargeable
  • Battery life: up to 10 hours continuously on (20 °C)
  • IP-Rating: Handheld meter IP67
  • Buoyancy: Positively buoyant in water
  • Dimensions
    • L x W x H: 21.8 cm x 9.4 cm x 5.3 cm (8.6 in. x 3.7 in. x 2.1 in.)
    • Weight: 0.68 kg (1.5 lbs)


  • Hydrolab communications modules: USB, SDI-12, RS232, RS485, or TTY. 
  • A USB Module is included with a sonde. Others are sold separately.

User interface

  • Hydrolab Operating Software on Microsoft Windows OS (Windos XP with Service Pack 3 or later)

Power requirements

  • External: 6–24 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.


  • 4 GB of internal memory; 1 second interval of continuous measurements with a 15 minute logging interval


  • Temperature sensor plus 4 additional universal sensor ports and optional depth

Operating temperature

  • –5 to 50 °C (23 to 122 °F), non-freezing
  • Operating outside this temperature range may result in mechanical damage or faulty electronic performance.

Sensors Specifications:

Temperature Sensor

  • Range: -5 to +50°C
  • Accuracy: ±0.10°C
  • Resolution: 0.01°C

Conductivity Sensor

  • Range: 0 to 100 mS/cm
  • Accuracy: ± (0.5% of reading + 0.001 mS/cm)
  • Resolution: 0.001

Hach LDO Dissolved Oxygen Sensor

  • Range: 0 to 60 mg/L, *Exceeds Maximum Natural Concentrations
  • Accuracy:
    • ± 0.1 mg/L at <8 mg="" l="" --8--="">
    • ± 0.2 mg/L at <8 mg="" l="" li="">
    • ±10% reading at <20 mg="" l="" li="">
  • Resolution: 0.01 mg/L

pH Sensor

  • Range: 0 to 14 pH units
  • Accuracy: ± 0.2 pH units*  (*Within the environmental pH range of pH 4 to pH 10)
  • Resolution: 0.01 pH units

Turbidity Sensor

  • Range: 0 to 3000 NTU
  • Accuracy: ± 1% up to 100 NTU, ± 3% from 100 to 400 NTU, ± 5% from 400 to 3000 NTU
  • Resolution: 0.1 NTU from 0 to 400 NTU; 1 NTU for >400 NTU

Depth/Vented Level 

Range (Vented Level) Accuracy Resolution
0 to 10 m 0.003 m 0.001 m
0 to 25 m 0.05 m 0.01 m
0 to 100 m 0.05 m 0.01 m
0 to 200 m 0.1 m 0.1 m


Datalogger Considerations

Compatible Contemporary Dataloggers

CR200(X) Series CR800/CR850 CR1000 CR3000 CR5000 CR7X CR9000X

Compatible Retired Dataloggers

CR500 CR510 CR10 CR10X CR23X 21X CR9000

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