Maker

AGA, Sweden

Model

Geodimeter Model 6A

Serial Number

61311

Dimensions

Length 360 mm, Width 220 mm, Height 530 mm,

Telescope length 355 mm

Image

Description

This Geodimeter Model 6A is a portable and precise medium range electro-optical distance meter capable of measuring distances up to 10 km in daylight and up to 25 m in darkness. The instrument transmits a light beam (wavelength 550 nm), to which is applied a modulation of approximately 30 MHz (10 m), i.e. the light is intensity-modulated. The beam is directed onto a reflector at the distant station, from which it is reflected back to the instrument. The incoming light is received by a photo-multiplier (hence converted to an electrical signal) and the difference in phase between the transmitted and received modulations is measured.

The Geodimeter basically consists of the following components: (1) Light source, (2) Electro-optical shutter, (3) Modulator, (4) Transmitting and receiving optical systems, and (5) Photo-multiplier and phase comparison unit. The light source is, for night and short-range daylight work, an ordinary tungsten-filament lamp; and for daylight operation over longer lines, a mercury-vapour lamp.

The instrument has two optical systems, one for transmitting the modulated light and one for receiving this light after reflection from the reflector at the other end of the line. There is also a searchlight and a coarse sight, which are used for easier location of the reflector. The searchlight is placed under the main tube and consists of a 2 W bulb, placed at the focal point of the projection lens. The course sight has a field of view and a magnification selected to facilitate the reflector location, and is equipped with a reticle which is illuminated when the panel light is on.

The magnification of the "receiver" optics, which is placed in a tube coaxial with the central tube, is 28x, with a focal length of 0.6 m and an objective diameter of 50 mm. The "transmitter" optics, located on the outside of  the receiver optics, has a focal length of 0.6 m, and inner and outer objective diameters of 55 mm and 105 mm respectively. 

The power source required for the instrument is a 12 V dc battery. The distance meters average power consumption, which depends upon the operating conditions of the thermostats and lamps, is approximately 2.5 A. The precision using the standard method of measuring, with a measuring time of about 5 minutes, is less than (5 mm + 1 mm/km). However, when using the precise method of measuring, the readings could take as long as 30 minutes with a standard deviation of less than (1 mm + 1 ppm). 

History & comments

Please note that the images above are that of 0412. The instrument (S/N 61311) listed here is fitted with the Kern centring system (not the Wild centring system shown in the images).

Conservation

Aluminium transport case (280 x 480 x 630 mm).

Condition

Good

• Instrument was donated by 'Geodimeter Australia'
• This instrument is one of the two model 6A's in the collection.
• Weight of instrument is 16.3 kg.
• Weight of transport case is 8.5 kg.
• Catalogued by T. Ko
• Updated by F. Pall

Dates

Manufactured in 1966 (approx). Catalogued in 2000.