The german logging company BLM in Gommern asked to refurbish six vintage Density logging tools type DGGS60. They have to run the probes on Antares Aladin logger. Working with GEOCOM 16 bit digital data communication protocol and 100 mA constant current supply on a single wire of a logging cable.
The Density Probe has two Gamma-sensors, composed of photomultiplier tubes and scintillator crystals. There is 20 cm distance between the short-space and long-space sensor. The Gamma-sensors are carefully shielded with cutoff lead parts.
We had to preserve the useful mechanic frame incl. lead parts and to completely swap the old density sensors including the old electronics.
The old scintillator crystals were partly blind and were substituted by Crydet Type G18x30S.
A comparison of photomultiplier tubes with voltage divider: old tube from 1980 with discrete resistor divider and the new Hamamtsu R6094 with SMD divider.
The High Voltage boards generate 1250 Volts to supply the Hamamatsu R6094 photomultiplier. The output of the photomultiplier are pulses, which are counted.
The ATmega88 board handle the one wire pulse communication between the probe and the uphole logging station. Power is supplied by DC constant current over the same wire of a logging cable.
This ATmega88 board is designed for multiple application as there are: 4-arm caliper, Gamma, Gamma FEL, Temperature, etc. It has several counters, 8-channel 10 bit ADC and 4- channel 24 bit A/D converter, UART, etc. This board allows building slim hole logging probes down to 30 mm diameter.
For the DGGS60 application the boards are configured for 100 mA constant current supply and uses two counters for the short space an long space gamma sensors. The firmware running on the board recognises the data request impulse from the logging station and sends a four 16-bit-words pulse train up. Gamma counts are sampled 10 times per second.
The ATmega88 bord and the High Voltage board had to be mounted on an aluminium carrier.
The internal frame is build of blooming steel sheet, has a diameter of 48 mm and a length of 750 mm. The outer diameter of the stainless steel probe is 60 mm.
We wish the best for the next 30 years.