Positron emission tomography (PET) has become a key technology for molecular imaging in clinical practice, as well as in medical, biological and pharmaceutical research. This increases the necessity for a practical introduction to PET in students with a corresponding specialization. For this purpose, the PET scanner 'PET-TW 05' was set up to demonstrate both the principles of computer tomography (CT) as well as the basics of PET. Moreover, the technical requirements and the signal processing needed for a PET system are shown in a simplified but comprehensive way. This article illustrates the layout of the tomography and provides an overview on the signal processing, as well as on the details of data acquisition and processing. The measuring procedure is described. The results for a measurement with a simple source configuration (five 22Na sources) are also presented. Finally, the characteristic parameters and the educational goals of the tomograph are summarized.