The Instrumental Errors of the LLMC

The instrumental errors of the LLMC can be classified into processing errors, assembling errors and other errors from the deformations caused by gravity and heating.Among the processing errors, there are privot errors and the processing errors from the azimuthal positioning system besides the graduation errors in the divided circle.Among the assembling errors, there are the assembling errors of the divided circle, the reading scope and the telescope as well as the azimuth error, and the level error and collimation error existing in traditional meridian circles.Among the errors from the deformations caused by gravity and heating, there are the variation of optical axis from the flexure of the tube and the variation of the zenith point of the graduation circle caused by the heat deform ation to the supportor of the reading scopes.Moreover, there are the variation of small displace and rotation between the prim ary and the secondary mirror in the tube at different temperatures, resulting in the change of the optical axis, the variation of the orientation of the level axis caused by the different temperatures between the left part and the right part of the axis and etc.All these errors need to be mearured and corrected from the observational results.There are some auxiliary optical systems to measure all the errors mentioned above, which include the inspecting system of the azimuth, electric level, axial collim ating device and autocollimating plane mirror in the tube.Tw o specialities of the LLMC to measure and correct the instrumental errors are introduced in this paper.One is the direct elimination of some instrumental errors by rotating the horizontal axis w ith 180 degrees.The other is the real time measurement of some errors.