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STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

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MWD and LWD 909<br />

continuous component to be measured, must be less than the instrument’s<br />

measurement range.<br />

These instruments serve to measure the earth’s gravitational field with a<br />

maximum value of 1 g. The typical values of the characteristics are:<br />

scale factor, 3 mA/g<br />

resolution, g<br />

skew, g<br />

service temperature, -55 to +15OoC<br />

For measurement ranges from 0 to 180°, three accelerometers mounted<br />

orthogonally must be used as shown in Figure 4-224. The x and y accelerometers<br />

are mounted with their sensitive axis perpendicular to the tool axis. The z<br />

accelerometer is mounted with its sensitive axis lined up with the tool axis.<br />

2-ACCELEROMETER<br />

HOLDING POlN T<br />

Y-ACCELEROMETER<br />

X-ACCEtEROMETER<br />

CONNECTOR<br />

OLDlNG POINT<br />

FERENCE PIN<br />

Figure 4-224. Mechanical drawing of the accelerometer section of a<br />

directional tool. (Courtesy Sunstrand [102].)

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