Gestra Gmbh

Juergen Klattenhoff

Guenter Schmitz

Joachim-Christian Politt

Holger Schroeter

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.

Controller for heat engineering installations

A measuring instrument ( ) for fill level sensors ( ) having a measuring electrode ( ) and a compensating electrode ( ). The measuring instrument ( ) has a bridge circuit whose one bridge branch ( ) is formed by two series-connected test resistors ( ). The other bridge branch ( ) is formed by the measuring resistor ( ) on the measuring electrode ( ) and the compensating resistor ( ) on the compensating electrode ( ). Between the two bridge branches ( ) a diagonal line ( ) with a test switch ( ) is provided. The measuring instrument ( ) is controlled by the control circuit ( ) so that the diagonal line ( ) is closed outside of preset test time periods, and interrupted at preset test time periods. The end of the diagonal line ( ) located between the two test resistors ( ) is connected to the base potential ( ) of the measuring circuit ( ). The resistors ( ) are designed so that when the test switch ( ) is closed, the imbalance of the bridge is determined by the second bridge branch ( ), whereas when the test switch ( ) is open, the imbalance of the bridge is determined by the first bridge branch ( ), simulating in this way a situation in which the fill level has dropped below the limit value. The control circuit ( ) provides an error signal if the signal of measuring circuit ( ) is not corresponding. In this way, the measuring instrument ( ) automatically tests its functionality.

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Delmenhorst, Germany

Juergen Klattenhoff