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  Surveying Instrument Collection 


Kern & Co., Aarau, Switzerland


DM 501

Serial Number



Length 180 mm, Width 70 mm, Height 180 mm


Kern DM 501Kern DM 501


This Kern DM 501 short-range electro-optical distance meter has the ability to conveniently snap on to the telescope of a Kern theodolite such as the Kern K1-SE scale-reading theodolite as shown in the above images, thus producing a complete all-in-one theodolite and distance measuring instrument (see 0215 for details on the host theodolite).

The distance meter slots into holes on the objective side and rests on adjustable screws on the eyepiece side. It is pressed on these screws by springs on the other side. The adjustment of the distance meter's line of sight (to that of the theodolite) was with the aid of these screws, on the eyepiece side.

The EDM consists of two telescopes, a transmitting telescope and a receiving telescope with objective diameters of 28 mm each. An infrared filter and a diaphragm (for adjustment of the signal strength) is mounted inside the receiver optics. Both telescopes are small enough to allow the main telescope of the theodolite to rotate through 360° about the horizontal (trunnion) axis.

The instrument uses a digital phase measuring method with an infrared 900 nm Ga-As-Diode (Gallium-Arsenide-Diode) as radiation source. The modulation fine measurement frequency is 15 MHz and the power requirement for distance measurement is 11 Watts. The maximum range of distance measurement for the instrument is approximately 1.0 km using a single prism, and 1.6 km using a triple prism. The standard deviation of one distance measurement is ±(5 mm + 0.000005D), where D represents the distance in km. The instrument also operates in tracking mode, where the slope distance is displayed every 2 seconds.

The power is provided through the wiring for the circle illumination, with the battery attached to the stationary base of the host theodolite. The energy is supplied through slip rings on the axes and contact tongues on the telescope. This means that the theodolite can be used without interference by cables.

History & comments

Mr. René Nünlist (Chief of Electronics at the Development Section of Kern) manufactured the shell of the prototype of the DM 500 himself from a block of metal during the factory holidays in 1970. The DM 500 was first shown in 1971 at the Spring Convention of the ACSM in Washington DC.


Plastic case





Triple reflector

  • Instrument includes a set of 4 reflectors, three of which can be joined together to form a triple reflector (refer to left image)
  • Also included is a battery power supply set
  • Weight of instrument is 1.6 kg
  • Catalogued by T. Ko
  • Some comments are courtesy of the Kern Collection of the Aarau City Museum, Switzerland.
  • Updated by F. Pall


Manufactured in 1970 (approx). Catalogued in 2000.

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