Tegtmeyer Geophysik GmbH , a german logging company, desired to reactivate some fluid-resistivity / temperature probes, build by Geocom in 1988. The probes worked for years but the reliability dropped dramatically in the past until they were useless.
Fluid-resistivity / temperature logs
Fluid-resistivity/temperature (SalTemp) logs show anomalies in salinity, inflow zones and vertical flow in the borehole. The electrical resistance is measures between ring electrodes in a fluid cell. Temperatur values provide information on differences of stagnant fluid, indicating the flow of water in the borehole.
Old stuff from the eighties
Upgraded Probe from 2018
The upgraded probe is now equipped with a 25 mm PCB-bord with Atmel ATMega 88 micro-controller and 24-bit AD-Converter.
The firmware is written in C and programmed with Atmel Studio. Main task is producing a 125 Hz square wave current driving the outer electrodes, and syncronously digitization of the voltages from the inner electrodes witch represents the conductivity. Further tasks are math routines to get calibrated salinity and temperature values.
New specifications
Conductivity: 0.050 to 250 mS/cm with 1 µS/cm resolution
Temperature: 0 to 70°C with 0.001°C resolution
Logger: Antares Aladin DIMGC
Communication: Geocom 16 bit digital
Power: 100mA constant current
Cable: mono or 4-conductor
Precise calibration
Precise calibration of salinity was performed in circulating water with defined salt content of the fluid at a constant temperature. Calibration coefficient were calculated in an Excel-sheet.
