STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

MWD and LWD 933
for measuring the direction of the earth’s magnetic field and accelerometers for
measuring the gravity vector. An electromagnetic and electronic unit, every time
rotation is halted, calculates and memorizes the azimuth, drift and tool face
angles. Bottomhole electric power is supplied by an AC generator coupled with
a turbine situated on the mud stream in the drill collar.
In rotary drilling a rotation detector triggers angle measurements when the
string stops rotating with circulation maintained. With a downhole motor the
measurements are repeated as long as mud continues to circulate. The transmission
uses a ten-bit digital coding. Figure 4-244 gives a schematic diagram of
the positive pulse generator.
Maximum Valve
Travel \
MudValve -
Turbine %
Vibration
4
Isolator
A Valve
Actuator
. Generator
Electrical
Cable
- Centralizer
Sensor and
Electronics Package
, Vibration
Isolator
Figure 4-244. Schematic diagram of the positive pulse system. (Courtesy
Inteq-Teleco [105].)