National Instruments NI USB-621x Isolation and Digital Isolators

11

Isolation and Digital Isolators

USB-6215/6218 devices are isolated data acquisition devices. As shown in Figure 11-1,the analog input, analog output, counters, PFI/static DI, and PFI/static DO circuitry, and digital routing and clock generation are referenced to an isolated ground. The bus interface circuitry is referenced to a non-isolated ground. Refer to Table 11-1for an example of the symbols for isolated ground and non-isolated ground.

Table 11-1.Ground Symbols

Isolated Ground Non-Isolated Ground

I/O Connector

		Isolation
		Barrier
Analog Input		(USB-6215
		and USB-6218
		devices only)
Analog Output
	Digital
	Routing	Digital	Bus	Bus
Digital I/O
	and Clock	Isolators	Interface
	Generation
Counters
PFI

Figure 11-1.General NI 621x Block Diagram

The non-isolated ground is connected to the chassis ground of the PC.

Each isolated ground is not connected to the chassis ground of the PC. The isolated ground can be at a higher or lower voltage relative to the non-isolated ground. All analog measurements are made relative to the isolated ground signal.

© National Instruments Corporation 11-1 NI USB-621x User Manual