The Impact of ASICs

Techniques such as those discussed above were first developed on large computers and ultimately implemented on microprocessors. These were stiU comparatively cumbersome, requiring a circuit board to be associated with each sensor. At this stage it is worth emphasising why the compensation needs to be done at the sensor site. In a large industrial instrumentation system the central computer could be overburdened with sensor compensation processing, while the communication system could be overloaded by raw uncompensated sensor data. Ideally the compensation and communication electronics should be contained in the sensor housing and should be functionally invisible to the user. 

Also at this point we come up against one of the major problems and a source of cogent criticism of the very concept of intelligent sensors. It has always been a truism that the more complex a system is the less reliable it is. Fortunately this principle can be reversed by the introduction of two 

The development process on such systems could be fraught with complexity, so it is important to establish methods that give the designer maximum support. A very useful technique is to embed the ASIC in a PC as shown in Fig. 7.7. Data acquisition boards are used to provide intimate access to the functions of the chip. Software is developed in a portable language, such as C, which allows it to be ported onto a suitable microprocessor once it has been developed and tested [15]. This leaves the question of support software which is discussed in the following section. 

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