Development on telemetry system for deep borehole sensor network

We are developing the borehole telemetry system which can have 8 modules (in maximum) on single conductor cable with the sensor I/F such as digital inputs, analog inputs, and power supply. Here, we set the engineering specification of mean time to failure (MTTF) as 5 years under the environmental conditions of borehole depth as 3500 m, pressure, 104 MPa, and temperature, 125°C. After the evaluation tests on primal components, we built the prototype of the telemetry system to evaluate on high temperature life, shock, vibration, and also to carry out the field test using land well with simulating the actual configuration. As one of the results, MTTF of this prototype, to which the ready-made plastic components were applied, was obtained as about 0.9 years against 125°C, 23 years against 85°C.