Keller DCX 22 CTD
The DCX-22-CTD data loggers measure conductivity and temperature as well as pressure, along with the depth of bodies of water. The integrated Pt1000 achieves an accuracy of ±0,1 °C, and the conductivity can be measured at ± 2,5% of the selected range (0,2 / 2 / 20 / 200 mS/cm). Thanks to their long-life battery, they can keep recording measurement results for years (up to 10 years at a rate of one measurement per hour). The logger can be configured using the supplied software (measurement interval, incident management, delayed measurement start etc.) and data that has been read can be displayed in a graph or chart, corrected using air pressure values, converted into fill levels or other units, and exported.
The CTD versions of the DCX-22 range are autonomous battery-operated data collectors made of stainless steel. Requiring little maintenance, they record the water level (pressure), tempe- rature and conductivity over long periods. CTD stands for Conductivity, Temperature and Depth.
This data sheet specifies the additional conductivity measurement function which distinguishes the CTD version from the standard DCX-22. The pressure and temperature specifications are set out in detail in the data sheets for the DCX-22AA and DCX-22(SG/VG).
Conductivity is increasingly being monitored in conjunction with depth measurements, in which changes in water quality and depth are required to be detected simultaneously. Thus it is possible to detect contamination caused by salt water, waterborne particles or general pollutants when measuring groundwater levels.
KELLERʼs KOLIBRI Desktop programming and readout software is used to select a conductivity range (0...0.2 mS/cm, 0...2 mS/cm, 0...20 mS/cm or 0...200 mS/cm) and set the temperature coefficient for the medium. This process produces compensated conductivity measured values standardised at 25 °C.
The DCX-22AA-CTD data collector records groundwater levels using the AA (absolute- absolute) measurement method, whereby fluctuations in atmospheric pressure are measured and compensated for by the watertight atmospheric pressure sensor with its stainless steel dia- phragm. The advantage of this measurement method is that no humidity-sensitive capillary tube is required. As well, it is not required that the DCX-22AA-CTD be removed from the immersion tube in order to extract the data.
In the DCX-22-CTD, the sensor, electronics and battery are contained within the same housing. The data collector needs to be withdrawn from the immersion tube in order to extract the data. The DCX-22-CTD uses an absolute pressure sensor. For long-term measurements, where the impact of atmospheric pressure fluctuations is to be compensated, a second DCX, acting as a barometer, is placed at the surface to record changes in atmospheric pressure. The pressuredifference or, as appropriate, the water level is then calculated in the Kolibri Desktop Software by subtracting both measured values.
The DCX-22SG/VG-CTD versions have a cable outlet with a readout plug, which is fixed to the surface of the measuring point with a locking disc. This means that the data logger does not have to be pulled out of the measuring point to read out the data. In the VG version (reference pressure measurement), the reference equalisation capillary tube in the cable is inserted until the read-out connector, where the reference opening protected by a Gore-Tex® diaphragm is located.