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MODULAR INSTRUMENTATION DESIGN

Part 1ýDefining the Project
by Bob Perrin

Start • The Problem ý The Solution ý Mechanical Interface ý Man Machine Interface ý Electrical Interface ý API ý In Closing ý Sources and PDF

MECHANICAL INTERFACE

Instrumentation generally falls into one of four categories.

• Hand-held
• Bench-top
• Industrial
• Harsh environment

The last one is the most difficult, as it depends entirely on the developerýs application. It might be possible to come up with some sort of enclosure that is NEMA 4, or even 4x. However, because the harsh-environment market is probably the smallest and most specialized, we will leave design of this packaging on the back burner.

Industrial packaging generally means some kind of enclosure that is dust proof, easily mounted, and offers quick-disconnect screw terminals. PLCs and many packaged embedded controllers fall into this group.

For hand-held instruments, a stock Serpac or OKW enclosure can be adapted. These boxes usually have a top half that can be mated to bottom halves of various depths. This will provide the developer with options if sensors or additional specialized electronics or connectors must be added. Locating a suitable, inexpensive enclosure will be part of this project

Another implication of hand-held instruments that is related to packaging is battery storage. Electrically, the controller should be low power. Mechanically, the batteries should be easy to change. (The enclosure should accommodate between two and four AA batteries.)

The application developerýs idea of a bench-top enclosure is perhaps the most difficult to second guess. Aesthetics and ergonomics are impossible to determine in advance. The best we can do is to keep the controller on the small side, with convenient mounting points and easily accessed connectors.

We must come up with a controller and a packaging system that allows simple integration in a hand-held enclosure and easy mounting in a bench-top enclosure. For industrial applications, the controller should support quick disconnect screw terminals and be small enough that it can be integrated into bench-top and harsh-environment designs.

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