[en] The heavy ion accelerator UNILAC is composed of a 320 keV preaccelerator, various rf cavities and some independent r-f components to affect the beam bunches. For adjusting and operating these components correctly the intensity distribution of the beam in the longitudinal phase space has to be measured exactly. To this end electromagnetic probes have been designed and tested. In the following the optimization of such probes is considered. Based on experimental and theoretical investigations of the probe and data processing system some results are discussed. (FKS) 891 FKS/FKS 892 CKA