Back in early March I blogged on the topic of isolation as it related to industrial networking products and the concept of investing in isolated network products as a form of insurance. It turns out the topic of isolation is also relevant to data acquisition hardware solutions. This topic is also relevant to a more recent blog in which we discussed the importance of accuracy and how that rated as the most important technical requirement cited by almost 600 survey respondents.
As the accuracy of a user's data acquisition measurements go up so does the need to protect their signals from noise as well. The user needs to protect their signal on its entire path from the sensor input to the point of data conversion. In harsh environments such as those found in steel mills, automotive assembly, food & beverage and other applications in which the adverse impact of EMI, noise and other threats maybe more prevalent as is the need to protect against ground currents. Isolation eliminates ground loops between the measurement system and the signals you want to measure and protects the operator and equipment from effects of ground loops and high common mode voltages.
Isolation is defined as separation of one signal from another to prevent unintentional interaction between them. All multiplexed data acquisition systems contain a certain degree of channel-to-channel isolation; relay-based systems have galvanic isolation while solid-state systems do not. Galvanic isolation is the absence of any DC path. Most isolation methods eliminate all DC paths below 100 MΩ. Three major benefits of galvanic isolation are circuit protection, noise reduction and high common-mode voltage rejection, especially those developed by ground loops.
PC based data acquisition solutions makes possible an array of multiple channel measurements previously beyond economic reach of many applications. This has been accomplished by two major compromises, multiplexing and non-isolated inputs. Multiplexing is successful when the sampling rate is adequately high and the source impedances are sufficiently low. Lack of isolation places an entirely different kind of limitation on the type of input signals that can be connected.
If an application operates in an environment in which the need for isolation is prevalent VDC recommends users consider investing in a data acquisition solution with built-in isolation. Although there may be a cost premium associated to investing in a data acquisition solution with isolation, VDC believes that this will prove to be a wise investment in insuring that the data acquisition solution and equipment being monitored will provide a quick payback if the catastrophe of equipment failure is averted.
Although the topic of isolation is not an integral part of the scope of VDC's 2011 Data Acquisition Solutions Market Intelligence Program we are always interested in covering topics which are germane to relevant research related issues or dynamics impacting the industrial automation world.
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