New Isolation Technologies Ensure Safety at Lower Cost
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It is a dangerous world out there. Transients, hazardous high voltages, and electrical noise are constantly attacking your data acquisition and control equipment. Your equipment and, more importantly, your data may need protection against these potentially harmful sources. Isolation can provide this safety by physically separating the unsafe part of the circuit from the rest of the data acquisition system. It also can improve measurement accuracy by preventing ground loops and rejecting common mode voltages. With new isolation technologies, you can meet these needs without spending a lot or hampering performance.
New Isolation Technologies
New high-speed digital isolation components are helping to lower the cost and increase the performance of industrial analog data acquisition devices. Traditionally, optocouplers have been a common digital isolation method. Newer digital isolation technologies, such as the iCoupler from Analog Devices, make use of chip-scale transformers to offer several channels of isolation in a small package. These components employ high-speed CMOS technology for increased data rates. They also are smaller than optocoupler circuits and significantly reduce power consumption.
New National Instruments industrial data acquisition devices such as the C Series modules, used in CompactRIO and high-performance USB devices, and upcoming isolated multifunction plug-in PCI and PXI devices incorporate these new isolation components to achieve high-speed isolated measurements. For instance, the NI 9201 module for CompactRIO offers 2300 Vrms isolation (withstand) for eight analog input channels and can sample at 500 KS/s.
Determining Product Safety
Some manufacturers specify data acquisition device isolation based on individual component isolation ratings. This is misleading because the isolation for a complete data acquisition device can be different from the isolation rating of its components. Device isolation depends on PCB trace separation, the spacing between high- and low-voltage circuits, and the distance between I/O connector pins and pins/traces to ground. Additionally, several other factors, such as protection covers and keyed connectors for high-voltage PCI boards, go into making data acquisition products safe. The best practice is to look for safety certification by an independent third party, such as UL, CSA, TUV, and others. These organizations evaluate products based on established safety standards that ensure the product is safe to use.
Learn more about isolation and isolated NI products or read application notes and an article on the benefits of isolation.
This article appeared in the Q1 2006 issue of Instrumentation Newsletter.
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