Spectra Laser Level AL20M User Manual

Features  
Maintenance and Care  
AL20M, AL24M, AL28M  
AL24A, AL28A, AL32A  
Auto Levels  
01. Focusing knob  
02. Sighting guide  
• As with all precision instruments, the auto level should be  
transported and stored in its carrying case.  
• When carrying the instrument mounted to a tripod, be sure  
to carry it vertically rather than over your shoulder.  
1
2
3
13  
12  
03. Crosshairs’ adjustment screws (under cover)  
04. Crosshairs’ focusing ring  
05. Eyepiece  
06. Horizontal rotation ring and angle index  
07. Leveling screws  
User Guide  
• Whenever possible, store the instrument in a dry, shady area.  
• Wipe the instrument clean with a cloth. Clean the objective  
and eyepieces with special care using a damp tissue or soft,  
clean, lint-free cotton cloth.  
• When working in wet weather, wipe off the instrument and  
carrying case in the field and let them dry completely indoors  
with the case open.  
4
5
11  
10  
08. Base plate  
09. Circular level adjustment screws  
10. Horizontal tangent knob  
11. Circular level  
12. Mirror for reading circular level  
13. Objective  
6
Safety Information  
9
Included in this manual are Cautions and Notes. Each of  
these words represents a level of danger or concern. A Caution  
indicates a hazard or unsafe practice that could result in  
minor injury or property damage. A Note indicates important  
information unrelated to safety.  
7
8
– 9 –  
120–  
131–  
142–  
Establishing an Elevation  
1. Set up and level the instrument.  
2. Set the grade rod on a known elevation (30.55 m) and take a  
grade rod reading (1.72 m).  
3. Add the grade rod reading to the known elevation to get the  
height of instrument or HI (1.72 + 30.55 = 32.27 m).  
4. Subtract the elevation of the point you want to establish  
(31.02 m) from the HI (32.27) to calculate the difference  
between the two points (32.27 – 31.02 =1.25 m).  
5. Go to the point you want to establish and adjust the height of  
the grade rod until the calculated difference (1.25) is centered  
in the crosshairs.  
How to Use the Instrument  
Taking Measurements  
Setting Up the Instrument  
1. Set up the tripod at a height appropriate for your use.  
Note: Make sure the tripod is stable and the tripod head is  
relatively level.  
2. Attach the instrument to the tripod.  
3. Level the instrument using the circular level as a reference.  
4. Focus the telescope crosshairs by turning the crosshairs’  
focusing ring.  
Determining the Difference in Elevation  
Taking a Distance Measurement  
Note: The instrument’s stadia lines allow you to determine the  
distance between the instrument and the grade rod.  
1. Take readings at the upper stadia  
15  
line (1.436 m) and the lower stadia  
a1  
b1  
line (1.152 m).  
14  
13  
12  
11  
10  
2. Calculate the difference between  
the two readings (1.436 – 1.152 =  
0.284 m).  
3. Multiply the difference by 100  
to get the distance between the  
instrument and the grade rod  
(.284 x 100 = 28.4).  
B
Aligning the Instrument  
1. Align the telescope to the grade rod using the sighting guides.  
A
2. Turn the focusing knob to bring the grade rod into sharp  
focus. Precisely sight the center of the grade rod in the  
telescope crosshairs using the horizontal tangent knob.  
1. Set up the instrument half way between two points (A and B).  
2. Take a reading at point A (a1 = 1.726 m) and another one at  
point B (b1 =1.259 m).  
Note: A slight deviation of the line of sight from horizontal  
will not cause any measuring error as long as the instrument  
is set up approximately half way between the two points.  
3. Subtract b1 from a1 to get the difference between the points  
(d = 0.467 m).  
Computation Example  
Elevation  
3. Check for parallax shift.  
Note: No parallax exists if the crosshairs and the grade rod  
graduations remain in coincidence even when you change  
your viewing angle (move your eye up/down and left/right in  
front of the eyepiece).  
Note: After the bubble in the circular level has been centered,  
the compensator corrects residual line-of-sight inclinations.  
The compensator does not, however, eliminate any tilts  
resulting from inadequate adjustment of the circular level or  
line of sight. These must be checked regularly (see Adjusting  
the Instrument for more information).  
Center Line Reading  
Distance Measurement  
Upper Stadia Line Reading  
Lower Stadia Line Reading  
Difference  
1.294 m  
1.436 m  
1.152 m  
0.284 m  
28. 4 m  
Note: Point B is 0.467 higher than point A because the  
difference is a positive number. If point B were lower than  
point A, the number would be negative.  
Distance (0.284 x 100)  
 
175–  
– 8 –  
153–  
164–  

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