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OTT CTD Sensor

Pressure sensor for longterm measurement of conductivity, temperature and water level

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
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  • 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

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