| 摘要 |
A measurement circuit in the output circuit of e.g. a sensor measures at the user circuit applied to its terminals against which voltage polarity it is connected. The detection of one of the two states is fixed in a storing element and the correct driver is switched to the output terminals. This state is maintained for as long as there is no change to the polarity at the output terminals. If e.g. through the replacement of a defective relay the terminals are interchanged, then the measurement circuit correctly restores the stored state, so that the correct driver is associated with the user circuit in each case. If e.g. through the replacement of a control card or system suddenly positively instead of negatively switching sensors are required, there is no need to replace the equipment. On switching in the voltage, the equipment is instead initialized, so that it is set in accordance with the new circumstances. |
