Angle comparison using an autocollimator

Project Description

It is proposed to use an electronic autocollimator as the transfer standard for the next EURAMET.L-K3 comparison. The reason behind this proposal is that several European NMIs do have CMC entries for autocollimator calibration and that these CMC entries so far have not been checked in an international comparison.
Experience at PTB with the recalibration of MWO-type autocollimators have shown, that these instruments seem to be suitably stable upon time and shipment processes within Europe or overseas. It is therefore proposed to use an MWO ELCOMAT 3000 as the transfer standard, which should be calibrated in its horizontal measurement axis only (for NMI instrumentation which only allows to calibrate the vertical axis, the AC can be rotated by 90° by means of a mount provided by PTB).
For automatic measurement setups the following procedures are proposed:

Measurement range: ± 100 arcsec in steps of 10 arcsec
Measurement range: ± 10 arcsec in steps of 0.1 arcsec

For manual measurement setups alternatively:

Measurement range: ±1000 arcsec in steps of 100 arcsec
Measurement range: ± 10 arcsec in steps of 0.5 arcsec

Further conditions proposed: 300 mm distance, use of full effective aperture (32 mm), use of high quality (λ / 100 (RMS) over 45 mm diameter) high reflective (approx. 100%) reference mirror (minimum size of 50 mm); alternatively use of reference mirror provided by PTB; If possible: Measurement at the specified values as indicated by the AC (i.e., positioning guided by AC).

Draft of Technical Protocol is available (and will be further refined) as well as PTB presentation on experiences and investigation of influences on AC calibration
MWO has indicated willingness to provide an ELCOMAT 3000 AC on loan for this comparison

Final Report 2018-03-08

The comparison has been completed and results are published in the KCDB.

Progress Report 2009-12-09

  • Technical Protocol finalised
  • Participant list finalised
  • TP sent to TC-L: request for TP distribution; request for KCDB registration


Length (L)
Ralf Geckeler, PTB (Germany)
Phone: +49 531 592 5220
Fax: +49 531 592 5205
Coordinating Institute
PTB (Germany)
Further Partners
BelGIM (Belarus)
NMIJ (Japan)
NPLI (India)
VNIIM (Russia)