A transport device with a monitoring device and a device for treatment of substrates with such a transport device is described below. 
A conveyor belt is known from U.S. Pat.  No.  2,472,526 A, in which a switch cam (cam 17) is provided in the shaft of the undriven feed roll for recognition of slowing or shutdown of the conveyor belt, and a three-way switch is arranged on this shaft, so that a circuit is closed in alternation by the switch cam, so that a capacitor (condensers 19, 20) is charged in alternation.  The two capacitors feed a relay (relay 22) in alternation, which is held on this account, the discharge time of each capacitor being sufficient, in order to hold the relay in the holding position until the other capacitor is charged again and can supply the relay.  Only if the conveyor belt moves more slowly than prescribed or even stops, because of unduly high load, is the discharge time of a capacitor no longer sufficient, in order to supply the relay long enough for the other capacitor to assume feed of the relay, so that the relay drops out and, as a result, a protection (relay 30) effectively connected to the relay interrupts power supply for the drive motor (electrical motor 15) of the conveyor belt.  The proposed circuit arrangement is demanding and requires a number of electromechanical components that are prone to disturbance.  In addition, the configuration of the three-way switch is chosen, so that friction between the contacts of the three-way switch (contact arm 16d) and the switch cam is as limited as possible, in order to reduce wear.  This device is not suitable for recording or evaluating the electrical potential of the feed roll. 
A transport device is known from AT 500 851 A4 for hot dip coating of metal strips, in which rotation of a deflection roll 4 arranged in the melting bath 3 is recognized by the fact that a permanent magnet 14 mounted on the deflection roll is passed by a fixed induction coil 15 during each revolution.  The electrical potential of the feed roll cannot be either recorded or evaluated in this device either. 
Consequently, there is a requirement for a transport device with a monitoring device that is suitable for recording and/or evaluation of the electrical potential of rotating components of the transport device.  This task is solved by the transport device and the device for treatment of substrates of the present invention. 
The described transport device is suitable for moving substrates through a vacuum coating unit, in order to coat them, etch them or treat them in vacuum some other way.  Such vacuum coating units typically have lock chambers, as well as a vacuum chamber arranged between the lock chambers, which can be divided into compartments with different functions, for example, pump compartments and process compartments.  The proposed transport device is naturally also suited for other installation types, in which substrates are passed by treatment devices, for example, continuous diffusion furnaces, etching devices, etc.  The transport device is particularly suited for installations in which treatment of the substrates occurs at very high temperatures.  The transport device is also readily suited for use in “dirty” surroundings, for example, during dry etching or vacuum coating, i.e., in methods, in which there is a hazard that the transport device will be undesirably coated with particles by deposition or condensation of particles.