The groove density parameters are important to VLS plane gratings monochromator. It is necesary to make sure that the parameters were specified and their errors were acceptable. A diffraction method was used to measure the groove density of VLS grating for system. It included a light source (He - Ne laser)

a collimator

a goniometer with angle encoder

a autocollimator

a linear stages

a detector(CCD) and the guting to be tested. The main error sources in the measuring system were analyzed in details. It turned out that the measuring system proposed was adequated for our purpose. A compensation method was analyzed for the monochromator if the groove density parameters were deviated from the design value.