We now need to deal with the oldest of human problems, the 'need' to want more! Now that you are building a system that is going to work someone, somewhere, once they see just how reliable radio telemetry is, will want more signals relayed from one point to another.
There are two types of expansion, site and system. The latter refers to the whole system expanding with the addition of extra sites which in themselves may never have to relay more signals than when originally installed. System expansion does however impact radio channel usage and planning for this is dealt with later in the book. The former problem, that where the I/O of the site increases, needs to be catered for at this stage of the project.
As noticed in the previous section the spreadsheet indicated what I/O was remaining after having satisfied the standing requirement. On larger systems such expansion is normally written into the specification owing to the very opening statement of this page. Such expansion is obtainable in two methods, either by supplying the modules even though the I/O is not used at first, or by catering for the physical space and connections but not actually supplying the modules. The latter option may not always prove more economical as return trips to a site are costly (especially if providing for the expansion is paid in advance), however, offering room for expansion but not physically supplying the modules may well prove worth while - especially in modular radio telemetry systems where the expansion is guided by the requirements as they emerge rather than planned by forecasting, a technique still to be perfected.
There is one 'expansion' not dealt with here as it is not, in the full sense of the word, expansion, this being the planning of a system that then, as a whole, becomes part of a larger system. A good example of this would be our simple reservoir/pumphouse link being incorporated into a major water monitoring and control system. This aspect was dealt with at the beginning of the book.
One final word on catering for expansion; Be aware of the overeager process engineer who wants everything but holds a small wallet. Catering for his wildest dreams may mean a huge cabinet holding nothing, and such will it remain. There is both argument for and against using modular cabinet systems as opposed to one large one. The main difference being the initial costs on a large single cabinet are high but expansion costs small but if the expansion never happens it's money wasted that could have been spent elsewhere, wisely.
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