OTT CTD Sensor

Pressure sensor for long-term measurement of conductivity, temperature and water level

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The OTT CTD is an integrated sensor and datalogger for measurement of water level, temperature, and conductivity in groundwater and surface water applications.
It features a robust ceramic measuring cell for long term accuracy and has outputs for salinity and total dissolved solids (TDS).  Its built in datalogger manages and stores all measurements at user-programmable intervals.

  • Surface water, Groundwater
  • Vented pressure cell and 4-electrode graphite conductivity cell
  • Waterlevel, Temperature, Conductivity
  • Measures and stores water level, temperature, and conductivity data
  • Water level: 0 … 4, 10, 20, 40, and 100 m Conductivity: 0.001…2.000 mS/cm, 0.10…100.00 mS/cm
  • ±0,05 % FS
  • Yes


Outputs for conductivity include specific conductivity, salinity, and total dissolved solids

  • Ceramic pressure cell provides industry-leading accuracy
  • Conductivity, depth, and temperature measurements are combined into a single device that easily installs in a 1” or larger well or conduit
  • 4 MB of memory provides capacity for over 500,000 data points—ideal for long-term deployments OR short-term, high resolution pumping studies
  • Can be powered for over 18 months with off-the-shelf alkaline batteries or over 5 years with lithium batteries
  • Ability to perform contact gauge control measurements without sensor removal, so no need to pull the cable for routine maintenance
  • Complete in-well solution: all components are inserted into the groundwater well, eliminating the possibility of instrument vandalism
  • Battery life: up to 5 years with lithium batteries, with alkaline options are also available.
  • Long-term accuracy: a robust ceramic pressure cell will not deform over time, and an accurate 4-electrode conductivity measuring cell provides outputs for salinity and total dissolved solids (TDS)
  • User-friendly interaction: only one program required to setup unit and download data, plus a simple infrared communication interface that provides easy on-site data download
  • Simple Maintenance: Infrared interface, batteries, and desiccant are accessible at the top of the well or pipe and no tools are required

Examples of Use

Continuous or real-time water level, temperature, and conductivity measurement of:

  • Groundwater wells
  • Streams, rivers, channels, and canals
  • Reservoirs, lakes, and wetlands

Ideal for monitoring:

  • Continuous water level networks
  • Short-term or long-term projects
  • Salt water intrusion
  • Aquifer storage and recovery
  • Estuaries and wetlands

Technical Data

Lifetime (@ 1 h interval)
with Lithium-batteries ≥5 years
with Alkaline-batteries ≥1.5 years
Interface Infrared (IrDA)
Memory 4 MB
Amount of values approx. 500,000
Measurement interval 5 sec … 24 h
Storage interval 5 sec … 24 h
Installation ≥ 1″
Material ABS, POM, stainless steel 1.4539 (904 L)
Com unit (incl. bat) approx. 0.410 kg
Sonde approx. 0.430 kg
Com unit L x Ø 400 mm x 22 mm
Sonde L x Ø 317 mm x 22 mm
Max system length 1.5 … 200 m ±1 % ±5 cm
Storage temperature -–40 … +85 °C
Protection class
Com unit IP67 (water column max. 2 m, duration max. 24 h)
Sonde IP68
Water level measurement
Measurement range: 0 … 4 m, 10 m, 20 m, 40 m, 100 m
Resolution: 0.001 m / 0.1 cm / 0.01 ft / 0.1 inch
/ 0.0001 bar / 0.001 psi
Accuracy: ± 0.05 % FS
Units: m, cm, ft, inch, bar, psi
Temperature compensated operating range –-5 …. +45 °C (icefree)
Temperature measurement
Measurement range: –-25 … +70 °C
Resolution: 0.01 °C
Accuracy: ± 0.1 °C
Conductivity measurement Measurement range selectable
Measurement range 1: 0.001 … 2.000 mS/cm
Resolution: 0.001 mS/cm
Accuracy: ±0.5 % of measurement value; (min ±0.001 mS/cm)
Units: mS/cm / µS/cm
Measurement range 2: 0.1 … 100 mS/cm
Resolution: 0.01 mS/cm
Accuracy: ±1.5 % of measurement value; (min ±0.01 mS/cm)
Units: mS/cm
Electrical data
Power supply Lithium or Alkaline batteries
3 x 1.5 V battery (LR6·AA, FR6·AA)

Download PDF 


OTT CTD – CE Konformitätserklärung | Declaration of Conformity | Declaration de Conformité
Operating instructions – Groundwater Datalogger OTT CTD
Leaflet – Groundwater Datalogger with Conductivity measuring cell – OTT CTD
Brochure – OTT Ground water measurement
OTT CTD – Firmware – EN
USB interface drivers – OTT IrDA-Link USB – EN
OTT Water Logger Operating Program