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NI SwitchBlock cards require the use of a safety interlock resistor, without which you cannot route signals to or from the analog bus.
To prevent the front connectors of NI SwitchBlock cards from exposing high-voltage signals when disconnected from NI SwitchBlock accessories, the cards detect whether a cable or other accessory is attached to the front connector. NI accessories for the NI SwitchBlock connect pin 96 to pin 48 through a 500 Ω resistor (500 Ω ±20%, 1/10 W minimum) built into the accessory. If the resistor does not connect these two pins, no matrix lines can connect to the analog bus.
If you create your own cable or custom test fixture for your NI SwitchBlock, incorporate the interlock resistor into your design to ensure that your signal lines are touch-safe when the test fixture or cable is removed. Additionally, incorporating the safety interlock resistor allows the operation of an integrated relay test when your fixture is disconnected.