Different Types of Isolation: Channel-to-Channel, Bank (Channel-to-Bus), and Channel-to-Earth Ground Isolation
Hardware: Compact FieldPoint, CompactDAQ, CompactRIO, Digital I/O (DIO), Instrument Connectivity Other>>Ethernet, Modular Instruments, Multifunction DAQ (MIO), PXI/CompactPCI, SCC
Problem: What are the differences between the types of electrical isolation NI offers on devices? I do not understand the differences between channel-to-channel, bank (channel-to-bus), and channel-to-earth ground isolation.
Solution: Isolation is the separation of physical and electrical components of two parts of the device. It protects computer circuitry and human operators, breaks ground loops, and improves common-mode voltage and noise rejection.
- Channel-to-Earth Ground Isolation
Isolation in-between the device's channels and the device's Earth ground. Channel-to-Earth isolation is represented in the figure below. Based on the Isolation Barrier in Figure 1, AI GND/AO GND/D GND (Vc) are all on the same bus, which is a different bus than Ve = Vd. This is the most fundamental type and is also included in bank and channel-to-channel isolation. Normally, this isolation type is present on NI 9000 series modules and some SCC modules.
Figure 1. Schematic of Channel-to-Earth and Bank Isolation.
- Bank (Channel-to-Bus) Isolation
Isolation where groups of channels share a single isolation amplifier and have separate ground planes from other groups of channels in addition to the Earth ground of the device. In Figure 1, Vc != Ve != Vd, represents channel-to-bus isolation, where != is defined as "does not equal".
- Channel-to-Channel Isolation
Each channel is isolated from every other channel and other non-isolated components. Figure 2 specifically represents channel-to-channel isolation. Like the previous figure, the diagonal hash mark area electrically separates the circuitry. As such, in Figure 2, Vb, Vd, and Vf are all on separate busses, whereas in Figure 1, they were equal (i.e. on the same bus).
Figure 2. Schematic of Channel-to-Channel Isolation.
Note: If the device has a channel-to-channel specification and has AI, AO, and DI/O, such as the NI 6154, the DI/O channels are bank isolated from the other channel-to-channel isolated AI and AO channels.
Related Links: KnowledgeBase 1RL9K2US: What is the Difference between Overvoltage Protection, Isolation, and Safety Isolation (Working Voltage) for FieldPoint?Developer Zone Tutorial: High Voltage Measurements and IsolationDeveloper Zone Tutorial: Isolation Technologies for Reliable Industrial Measurements
Attachments: 
ChantoEarthandBankIsolation.JPGChantoChanIsolation.JPG
Report Date: 01/21/2008
Last Updated: 02/03/2009
Document ID: 4HKFIMGP
