Computer apparatus for transmitting certificate to device in installation

A computer apparatus for transmitting a certificate to a device in an installation is provided. The computer apparatus has a coupling unit for establishing and breaking a connection between the computer apparatus and the device, a processing unit for transmitting a certificate to the device by means of the established connection, wherein the certificate is valid for a first time period and is issued by a certification authority based on a certificate request, and a receiving unit for receiving a further certificate request from the device by means of the established connection, wherein the further certificate request is designed to request a certificate for a second time period, wherein the coupling unit is designed to break the connection after the certificate is transmitted and the further certificate request is received. Thus, the certificate is updated by means of visits to the installation by a service engineer in the case of installations without a communication connection to a certification authority.