B&B Electronics USB-4751/4751L Digital I/O Connections, Dry Contact Support for Digital Input

3.3 Digital I/O Connections

3.3.1 Dry Contact Support for Digital Input

Each digital input channel accepts either dry contact or 0 ~ 5 VDC wet contact inputs. Dry contact capability allows the channel to respond to changes in external circuitry (e.g., the closing of a switch in the external circuitry) when no voltage is present in the external circuit. Figure 3-3 shows external circuitry with both wet and dry contact components, con- nected as an input source to one of the card's digital input channels.

Figure 3.3: Digital Input Connections

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