Why can the PROFTest II device not power its own bus terminal?
The PROFIBUS cable tester PROFtest II was developed to test an existing PROFIBUS system for proper installation. The basic condition for a stable functioning structure is the fault-free line routing as well as the powered terminal resistors at both segment ends. In real system operation, these in turn need to be supplied with voltage by the corresponding end device so that precisely this status can be checked for proper function. Electrical current coming from the PROFtest II would lead to a false result here at a defective end device and is therefore not sensible.