Abstract: A controller has two shunt lines connected in parallel with safety relays. For testing their switching capability, the safety relays are reversed to their idle positions and the change in voltage is monitored on their idle contacts. If voltage is missing, an error signal is issued. During the test, the parallel shunt line is closed so that the safety power line is not interrupted. Switching amplifiers having a response and action time which is a fraction of the preset response time of the safety relays control the safety relays. For testing the electrical control, the drives of the safety relays are switched to currentless and the change in voltage is monitored on the drives. If the change in voltage is inadequate, an error signal is issued. The safety relays remain in their operating positions during the test.

Abstract: The system provides for one single cable with four electrical conductors (16 to 19). Two of the conductors (18, 19) form a field bus line for the signal transmission, and the other two conductors (16, 17) form an energy line for providing energy supply. All signal transmitters (1, 2) and signal receivers (3, 4) are connected to the cable, and the cable (16-19) is fitted at both ends with a line termination (20-22). Each signal transmitter (1, 2) and each signal receiver (3, 4) has a field bus controller (8, 10). The entire signal transmission takes place via the two-wire field bus line (18, 19).

Abstract: In cases of application where the critical temperature occurs or could occur, safe monitoring of the level of the liquid was not possible heretofore because the physical properties of the liquid and of the gaseous medium present above the latter in the container no longer differ at this temperature. The method includes the temperature in the container in the monitoring of the level of the liquid. Below a lower comparative temperature value (Tu), the output signal of the evaluator unit is determined by the measuring signal of the level sensor. The measuring signal of the level sensor is disregarded above this value (Tu). The evaluator unit supplies an output signal that is on the safe side with respect to the level of the liquid. The comparative temperature (Tu) is below the critical temperature to an extent such that the inaccuracies in the measurement of the level sensor and the temperature sensor have no interfering effect.

Abstract: A probe for monitoring a medium within a container, which includes a mounting housing for mounting the probe on a container, a neck part attached at one end to the mounting housing, and at the other end to a radially cantilevered head housing. The head housing extends on only one side of the neck part. A sensor is attached to the mounting housing. An electrical conductor is attached to the sensor and extends through the neck part and into the head housing where it is connected to an electronic circuit, which is mounted inside the head housing. The head housing is made so that its dimensions in the radial direction of the neck part are greater than the dimensions of the neck part. The cantilevered mounting of the head housing allows heat from the container to dissipate into the atmosphere without contacting a significant portion of the head housing. The configuration of the head housing also allows easy access to the electronic circuit, even if two probes are placed in close proximity to each other.

Abstract: In the presence of a defect in the insulation cover of known probes, liquid medium can leak from the container into the interior space of the housing of the probe, and from there into the surrounding environment, and endanger or even injure persons present there. The probe housing has an interior space with two chambers. The first chamber, which is close to the container, is capable of withstanding the pressure prevailing in the container. A passage opening present between the first chamber and the second chamber for the sensor electrode, or for its electrical conductor, is closed by a movable closing part or a stationary closing element. In the event of leakage through the insulation cover, the pressure would be transmitted from the container into the first chamber, but could not propagate from there into the second chamber and on from there.