Spectra AL20M Folheto

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13 

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Circular Level
1. Set up the instrument.
2. Center the bubble of the circular level using the leveling 

screws.

3. Turn the telescope 180° (200 gon).
4  Check to see whether the bubble is still centered in the circle. 

If it isn’t, eliminate one half of the error with the leveling

screws and the other half with the two adjustment screws for 

the circular level.

5. Repeat the process until the bubble remains centered when 

the instrument is turned.

Taking an Angle Measurement
1. Set up the tripod so that it is over a hub.
  Note: Make sure the tripod is stable and the tripod head is 

relatively level.

2. Hang a plumb-bob from the plumb-bob hook on the tripod.
  Note: Make sure the plumb-bob is over the hub.
3. Attach the instrument to the tripod.
4. Center the plumb-bob over the pin in the hub by varying  

the length of the tripod legs or by shifting the instrument  

on the tripod.

5. Accurately align the telescope to the first target using the

sighting guides and a horizontal tangent knob.

  Note: The first target is a known point.
6. Set the horizontal rotation ring to 0.
7. Accurately align the telescope to the second target and read

the angle.

Trimble / Spectra Precision Division

8261 State Route 235

Dayton, Ohio 45424-6383

U.S.A.

N324

© 2012, Trimble Navigation Limited. All rights reserved.

Reorder PN 1211-0200B (03/12)

www.trimble.com/spectra

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13 

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4. Move the instrument and reset it up so that it is about 2 m 

behind point B.

5. Take another reading at point B (b

2

 = 1.462 m).

6. Add b

2

 to d to get value c (1.462 + 1.487 = 2.949 m).

7. Take another reading at point A (a

2

).

8. Compare value c (2.949) to a

2

. If the line of sight is correct,

both numbers should be the same. If they differ by more than 

4 mm, reset the grade rod on point A and turn the crosshairs

adjustment screws (unscrew the cover to expose them) until 

value c (2.949) is centered in the crosshairs.

  Caution: The upper and lower adjustment screws are  

counter-screws and must not be set too tightly.

9. Repeat the process until the line of sight is correct  

(c and a

2

 are the same).

1. Set up the instrument half way between two points (A and B)

that are 30 to 40 m apart.

2. Take a reading at point A (a

1

 = 2.423 m) and another one at 

point B (b

1

 = 0.936 m).

3. Subtract b

1

 from a

1

 to get the difference between the points  

(d = +1.487 m). Make sure you note whether value d is a 

positive or negative number.

  Note: Because the distance from the instrument to each of  

the points is equal, the difference in elevation is correct even  

if the line of sight is out of adjustment.

a

2

b

2

a

1

b

1

A

B

a

2 

= 2.423      b

2  

= 1.462      

+b

1 

= 0.936     -d 

  

= 1.487

d 

 

= +1.487    c 

  

=  2.949

For product recycling instructions and more information,

please go to: www.trimble.com/environment/summary.html

To recycle Trimble WEEE, call: +31 497 53 2430, and ask for the ÒWEEE

associate,Ó or

mail a request for recycling instructions to:

Trimble Europe BV

c/o Menlo Worldwide Logistics

Meerheide 45

5521 DZ Eersel, NL

Trimble / Spectra Precision Division

8261 State Route 235

Dayton, Ohio 45424-6383

U.S.A.

(888) 527-3771

(Toll Free in U.S.A.)

+1-937-203-4419 Phone

+1-937-482-0030 Fax

www.trimble.com/spectra

Trimble Kaiserslautern GmbH

Am Sportplatz 5

67661 Kaiserslautern

GERMANY

Tel +49-(0)6301-71 14 14

Fax +49-06301-32213

Trimble Export Middle-East

P.O. Box 17760

JAFZ View, Dubai

UAE

+971-4-881-3005 Phone

+971-4-881-3007 Fax

Trimble Navigation Singapore PTE Ltd. 

80 Marine Parade Road, #22-06

Parkway Parade 

Singapore, 449269

+65 6348 2212 Phone

+65 6348 2232 Fax 

Trimble Beijing

Room 2805-07, Tengda Plaza,

No. 168 Xiwai Street

Haidian District

Beijing, China 100044

+86 10 8857 7575 Phone

+86 10 8857 7161 Fax

www.trimble.com.cn

To locate your local dealer or authorized Trimble Service Center 

outside the U.S.A for service, accessories, or spare parts, contact

one of our offices listed below.

AL32A

AL28A

AL24A

AL28M

AL24M

AL20M

Magnification

32X

28X

24X

28X

24X

20X

Dampening

Air

Air

Air

Magnetic

Magnetic

Magnetic

Accuracy*

+/-1.0mm

+/-1.5mm

+/-2.0mm

+/-1.5mm

+/-2.0mm

+/-2.5mm

Leveling Accuracy @ 50m

0.5mm

0.7mm

1.2mm

2.5mm

2.5mm

2.5mm

Telescope:

Aperture

30mm (1.2 in.)

Telescope image

Erect

Field of view angle

1⁰20'

Shortest focus distance

0.60m (1.97 ft.)

Stadia constant

100

Addition constant

0

Dimensions (L x W x H):

Instrument

103 x 190 x 135mm  (5.2 x 7.5 x 5.3 in.)

Case

170 x 280 x 190mm (6.7 x 11 x 7.5 in.)

Weight:

Instrument

1.6 kg (3.5 lb)

Case

1.25kg (2.75 lb)

*

Standard deviation according to DIN 18723 on 1 km of double leveling