Instruction Manual for the GLP-2 Geological Compass

GLP-2 Instruction Manual for the Geological Compass

Product Implementation Standard: Q/HGY-2020

I. Uses

The primary applications of the GLP-2 geological compass include:

1. Measure the attitude of the strata: including strike, dip direction, and dip angle;

2. Topographic surveying: includes determining orientation (i.e., intersection positioning), measuring slope angles, and establishing horizontal control.

3. Measure the vertical angle.

II. Main Performance

1. The damping time of the magnetic needle (the time it takes for the needle to deflect by 90° and then come to rest in its original position) is 30–60 seconds.

2. Reading error:

a. The angular error between the readings before and after the magnetic needle rotates shall not exceed 0.5°;

b. At 0°–180° and 90°–270°, the error caused by eccentricity in the magnetic needle shall not exceed 0.5°;

C. The reading error of the protractor shall not exceed 0.5°.

3. Spirit level sensitivity:

a. The long level is 15′ ± 3′/2 mm

b. The circular level is 30′ + 5′/2 mm.

4. Instrument external dimensions: 73 x 62 x 28 (mm)

5. Instrument weight: 0.16 kg.

III. Principles and Structure

1. Principle: This instrument exploits the property of a magnetic object (i.e., a magnetic needle) to align itself in a specific direction along the magnetic meridian. By reading the scale on the graduated ring, the direction of the target relative to the magnetic meridian can be determined. Based on two selected measurement points (or known reference points), the position of another unknown target can be calculated.

2. Structure (refer to the schematic diagram): The instrument consists of a main body formed by the upper cover 6 and the outer case 13, connected via hinge 8. The upper cover houses a reflecting mirror 7, which enables the target to be reflected in the mirror; the exterior of the outer case 13 is fitted with a long sighting device 1, which, in conjunction with the small sighting device 5, allows for accurate aiming at the target. Inside the outer case are a graduated dial 2 and a magnetic needle 3, enabling direct reading of the target’s azimuth. A circular level 10 indicates the instrument’s horizontal position. A long spirit level 4 and an indicator dial 11 are used for measuring slope angles, with readings taken directly from the inclination scale on the steering wheel 12. Switch 9 serves as the magnetic needle braking mechanism. An adjustment screw for magnetic declination is provided on the bottom surface of the outer case.

This instrument features a compact structure, small footprint, portability, reliable accuracy, and stable performance.

IV. Instructions for Use

(1) Measurement of structural attitudes (including strike, dip direction, and dip angle)

1. Measure the trend:

The strike is the horizontal projection of the dyke.

Open the instrument’s top cover 6 to its full extent, set the local magnetic declination, and place the instrument’s two long sides against a characteristic (representative) surface of the rock layer. Keep the circular bubble level centered, then read the degree indicated by the north pole of the magnetic needle (the end of the copper wire coil serves as the south pole of the magnetic needle); this reading represents the strike of the rock layer.

2. Assessing tendencies:

Perpendicular to the direction of the face indicated by the orientation.

Place the short side of the base plate beneath the connecting hinge 8, or the back of the top cover, against the characteristic surface of the rock layer, ensuring that the circular spirit level remains centered. The reading indicated by the north pole of the magnetic needle at this point represents the dip direction of the rock layer.

3. Measuring and adjusting the toe:

The angle between the vertical and the plane of the horizon.

Open the top cover 6 to its limit position, align the instrument’s side handle parallel to the strike of the rock layer and press it firmly against the characteristic surface of the rock layer, adjust the bubble level to center, and read the degree indicated by the dial on the indicator; this value represents the dip angle of the rock layer.

In practical measurements, it is sufficient to determine only one of the two factors—strike or dip—since strike and dip are perpendicular to each other, differing by 90°.

(2) Topographic Surveying (including azimuth determination, slope angle measurement, and horizontal line identification)

1. Determine the orientation:

The direction and location of the target. Determining the target’s position is also known as intersection positioning.

① Measurement method when the target is above the line of sight (horizontal line).

Hold the instrument firmly in your right hand, with the back of the upper cover facing the observer and your arm close to your body to minimize shaking. Use your left hand to adjust the long sighting tube and the reflecting mirror, then turn your body until the image of the target and the tip of the long sighting tube are simultaneously reflected in the mirror and bisected by the mirror’s center line. Keep the circular bubble level centered, and read the degree indicated by the north pole of the magnetic needle; this reading represents the direction to the target. Repeat the same procedure at another measurement station to observe the same target. The two lines drawn from the two stations, each along the measured bearing, will intersect at the target, thereby determining its position.

② Measurement method when the target is below the line of sight (horizontal line).

Hold the instrument firmly in your right hand, with the reflecting mirror positioned opposite the observer. Keep your arm close to your body to minimize shaking. With your left hand, adjust the long sighting device and the upper cover, then turn your body until the target and the tip of the sight are simultaneously aligned within the elliptical aperture of the reflecting mirror and bisected by the mirror’s centerline; ensure that the circular bubble remains centered. The reading indicated by the south pole of the magnetic needle is the bearing of the target. Repeat the measurement at another station using the same procedure. By taking bearings from two stations and drawing lines along the measured bearings that intersect at the target, you can determine the target’s position.

2. Measure the slope angle:

The angle between the target and the observer’s line of sight and the horizontal plane.

Hold the instrument’s housing with your right hand, with the long sighting tube on the observer’s side; ensure the instrument’s plane is vertical to the horizontal, and that the long bubble level is positioned at the bottom. With your left hand, adjust the top cover and the long sighting tube so that the target and the aperture of the sighting tip are both bisected by the elliptical line etched on the reflecting mirror. Then, use the middle finger of your right hand to adjust the handle, observing through the reflecting mirror until the long bubble level is centered. The reading indicated on the dial mounted on the handle at this moment represents the slope angle of the target. To measure the slope angle of a particular slope, simply open the top cover to its full extent, place the side of the instrument directly against the slope, center the long bubble level, and read the angle—this will be the slope angle of that surface (identical to the dip angle in structural measurements).

3. Establish the horizontal line:

Rotate the long sighting device until it lies in the same plane as the box face, tilt the top cover to 45°, and ensure the sighting tip is vertical. Align the indicator with “0”; the line of sight through the sight hole on the sighting tip and the elliptical aperture of the reflecting mirror will then coincide with the horizontal line.

(3) Measuring the object’s weight at a right angle

Rotate the upper cover to its extreme position, then press the side of the instrument firmly against a representative flat surface of the object (such as a drill pipe). Adjust the bubble level until it is centered; the reading indicated by the dial at this point represents the object’s true vertical angle.

V. Precautions

1. The magnetic needle, the jewel bearing, and the top jewel are the instrument’s most critical components and must be carefully protected and kept clean to ensure the magnetic needle’s sensitivity is not compromised. When the instrument is not in use, it should be securely closed. Once closed, the switch and the dial-rotation mechanism automatically lift the magnetic needle, disengaging the top jewel from the jewel bearing to prevent wear on the top jewel.

2. Do not disassemble any hinges lightly to avoid loosening and compromising accuracy;

3. Avoid exposing the instrument to high temperatures and direct sunlight as much as possible to prevent air leakage and malfunction of the water chamber.

4. The pivoting parts of the hinge should be regularly lubricated with watch oil to prevent dry friction and subsequent failure.

5. The instrument should be placed in a well-ventilated, dry location, away from magnetic objects.

The data in the table are based on the latest International Geomagnetic Reference Model.

, time node: December 31, 2017

Harbin Optical Instruments Factory Co., Ltd.

HARBIN OPTICAL INSTRUMENT FACTORY LTD.

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