Pneumatic versus Electronic Equipment

Another area of concern, which has been alluded to before, is that when the computer acts like Big Brother the operator will become less familiar with the process. Then should something go wrong, he will be slower and less able to cope with an emergency. Huters16 suggests that this can be corrected by proper signals and displays within the control room. This of course means an increase in costs. 

No definitive answers can be given as to which system will be best in the future, since this is a rapidly progressing area. Only the questions can be raised. 

The death knell for pneumatic control equipment has been predicted for at least the past 15 years. So far this has not happened, but it is still predicted. The major reason why pneumatic equipment is so popular is that the pneumatic control valve is cheap and requires little maintenance. The pneumatic system also has the advantage of posing no problems in the presence of flammable substances. (Extreme care must be exercised if electrical signals are used in such environments.) One major problem with pneumatic systems is the delay encountered in sending a pneumatic signal over 300 ft (90 m). However, this can usually be avoided by mounting the controller next to the unit instead of in the control room. This does not affect the monitoring of the process, which can still be done in a remote location. 

The electronic system is obviously preferable if an online computer is to be used. Pneumatic equipment could be used, but the cost of interfacing equipment would make it more expensive. 

Since this is a batch system, it might be advisable to use direct digital control. Undoubtedly the throughput could be increased over that with the more traditional analog control system. However, the initial costs and maintenance expenses would also increase. To fully instrument the system would also greatly complicate the equipment required, especially for feeding the reactors (this is discussed later). An economic balance should be run to determine whether this is feasible. I feel it would not be warranted, and have chosen to instrument the plant in the traditional way. 

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