Instruction Manual for the GLP-3 Pocket Compass

Release Date:

2021-08-06

GLP-3 Instruction Manual for the Pocket Compass

Product Implementation Standard: Q/HGY06-2020

I. Uses

The GLP-3 pocket compass is primarily used for:

1. Measurement of structural attitudes: including strike, dip direction, and dip angle;

2. Topographic surveying: includes determining orientation (i.e., the intersection point), measuring slope angles, and establishing horizontal alignment;

3. Measure verticality;

4. Create a topographic map.

II. Main Specifications

1. Magnetic needle damping time: 30–60 seconds

2. Dial graduation: 1°

3. Circular level angle: 30′ ± 5′ per 2 mm (at 20°C)

4. Instrument external dimensions: 75.5 × 66 × 14 (mm)

5. Instrument net weight: 0.12 kg

III. Principles and Structure

This instrument features a compact design, small footprint, light weight, portability, and simple operation, while also delivering reliable accuracy and stable performance.

This instrument determines the azimuth of a target by reading the magnetic needle against a graduated dial, and it also incorporates a plumb-bob type protractor. Combined with readings from the tilt-angle scale on the steering wheel, it can determine the various slope angles of the target.

The instrument’s main body is formed by the top cover [1] and the housing [9], which are connected via a pivot shaft [3]. A reflecting mirror [2] is mounted on the top cover, allowing the target to be reflected in the mirror. Inside the housing are a magnetic needle [6] and a graduated dial [4], enabling direct reading of the target’s azimuth; additionally, a steering wheel [7], an angle-measuring device [10], and a circular level [11] are installed. The angle-measuring device allows various slope values of the target to be read from the inclination scale on the steering wheel. The circular level indicates the instrument’s horizontal position. The top of the housing is also equipped with a switch cap [5] and a sighting tip [8]. A 60 mm scale is engraved on the side of the housing for drafting purposes.

IV. Instructions for Use

1. Measure the attitude:

a) Measure the trend

The strike is the direction of the projection of a rock vein onto the horizontal plane. To measure the strike, open the instrument’s top cover to the horizontal position, place the instrument’s long side against a representative feature surface of the rock layer, and center the bubble in the circular level. The reading indicated by the north pole of the magnetic needle at this point is the strike of the rock layer (the end of the copper wire wrapped around the needle serves as the south pole).

b) Measure tendency

The dip is the direction perpendicular to the plane defined by the strike. To measure the dip, place the short side of the instrument or the back of its top cover against the characteristic surface of the rock layer, center the circular bubble, and the degree indicated by the north pole of the magnetic needle is the dip of the rock layer.

c) Measure the dip angle

The dip angle is the angle between the strike-slip plane and the horizontal plane. To measure the dip angle, first open the top cover to the horizontal position, then press down on the switch cap to ensure that the instrument’s side is perpendicular to the strike and tightly against the characteristic surface of the rock layer. The reading indicated on the protractor dial is the dip angle of the rock layer.

Since strike and dip are perpendicular to each other, in practical measurements it is sufficient to determine only one of these two parameters; in most cases, only the strike needs to be measured.

2. Topographic surveying:

a) Determine orientation

Azimuth determination, also known as intersection positioning, refers to the direction and location of a target. Open the instrument’s top cover, hold the instrument firmly in your right hand with the reflecting mirror facing away from your arm (when the target is below the horizon, the mirror should face your arm) and press it tightly against your body to minimize shaking. Then, use your left hand to adjust the reflecting mirror and turn your body until the target is reflected in the mirror and bisected by the mirror’s centerline. At the same time, align the sighting notch with the mirror’s centerline and keep the circular bubble level centered. The degree indicated by the magnetic needle’s north pole at this moment is the azimuth of the target.

Using the same method, measure the target at another measurement point; the two direction lines obtained from the two measurements will intersect at a single point, which is the location of the target.

b) Measure the slope angle

The slope angle is the angle between the line connecting the measurement point to the target and the horizontal plane. During measurement, open the top cover to approximately 45°, use your left hand to adjust the cover so that the reflecting mirror aligns with the protractor, and hold the instrument housing with your right hand while tilting the protractor downward. Then, sight along the aiming point, the sight line, and the target; the reading indicated on the protractor scale at this moment is the slope angle of the target.

When the instrument can directly contact the target’s slope surface, simply press the instrument’s measuring face firmly against the target’s characteristic surface; the angle indicated by the protractor on the handlebar then represents the slope angle of the target.

c) Establish a horizontal line

Establishing a horizontal line involves determining whether two or more targets lie in the same horizontal plane. During measurement, tilt the upper cover to approximately 45°, then use your left hand to adjust the upper cover so that the reflecting mirror aligns with the protractor. Aim at the target through the sighting notch and the sight tube, record the reading indicated by the protractor, and then, at the same measurement point and at the same height, measure another target using the same method. If the readings indicated by the protractor are identical, this confirms that the two targets are located in the same horizontal plane.

3. Measure verticality:

Open the instrument’s top cover to a parallel position, then place the instrument’s long edge against the object’s reference surface. If the protractor reads 90°, the object is vertical.

4. Create a topographic map

On the map, place the instrument with the graduated scale against the survey point (or a known target), then rotate the instrument until the degree indicated by the north end of the magnetic needle matches the degree measured on the ground. At that point, draw a straight line along the instrument’s edge; this line represents the direction to the surveyed point. The intersection of two such direction lines is the location of the target.

V. Instrument Adjustment and Maintenance

1. The switch cap is a magnetic-pin locking braking mechanism; when the device is not in use, the top cover should be closed to lift the magnetic pin and prevent wear on the spindle tip.

2. The instrument should be protected as much as possible from impact and contamination, and shielded from prolonged exposure to high temperatures and rainwater. This is to prevent air leakage in the water bath and degradation of the mirror coating, which could compromise the instrument’s performance and accuracy.

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