Size is a critical issue in medical electronics because space is at a premium in hospital rooms, labs, and clinics. So when designing instrument cases, it's important to maximize density and performance. Modular enclosures let engineers do so without high tooling costs or starting from scratch.

An alternative to modular medical instrument cases would be off the shelf designs. But these can be difficult to find in the right size and shape. That often makes it necessary to use custom designs or settle on a size that is not quite right. There is also more risk relying on custom parts because they create problems such as single sourcing and obsolescence. A “right-sized” modular design for enclosures can solve these problems.

Aluminum extruded frames help make such enclosures possible. The extrusions are easily cut to length and internal parts in various sizes are easy to add for an instrument case. When the enclosure includes a card cage, injection molded guides can be popped into holes in the extrusion. Flexibility in locating guides means various card sizes and types can be placed in the enclosure.

Interlocking extrusions can be shaped to accept tapped strips, sealing cords for EMC, and directly mounted panels or PCBs, grounding terminals, and screws. This flexibility keeps costs low by eliminating a few manufacturing steps. Further, some extrusion shapes allow joining extrusions and panels, at times to add stability. Various extrusion styles can be used in different enclosure models for different purposes. All are easily cut to length.

The extrusion shape eliminates having to drill and tap it. So when an enclosure calls for a simple design, its few pieces are assembled quickly and easily. The benefit is an exact-sized case customized at a low cost, and even in low volumes. Typically, this kind of customization would require special tooling and only be cost-effective in high volumes. For example, a modular enclosure can cost as little as $100.00, while a customized enclosure can cost up to $3000.00 in tooling and nonrecurring engineering charges alone.

Modular enclosures can also shorten assembly times over previous practices. For example, a mounting panel can be used to attach the PCB, so the OEM can avoid from having to drill into the bottom of the enclosure. Instead, the mounting panel attaches to the bottom of the enclosure and sits about 0.25 in. off the bottom, allowing clearance for fasteners.

The PCB can attach to a mounting panel outside the enclosure for easy access. Doing so also shortens assembly time. Once the electronics check out, grooves in the side walls allow sliding the boards into the enclosure without further mounting or customization. In addition, the PCB can mount to the front panel. This provides an extra secure mount and saves even more time.

T-shaped grooves in the extrusion assist with mounting tasks. The grooves can hold mounting panels horizontally or vertically in the case. All types of components (fans, power supplies, and tubes) quickly mount without customization. Further, the grooves allow placing grounding terminals where needed.

Electromagnetic compatibility is another important consideration because medical electronics must not interfere with other equipment or be susceptible to interference. The top and bottom extrusions, and front panels have conductive connections (HF shield) to protect against EMI. The top and bottom-cover edges are folded over during forming to facilitate a tight seal and improve the unit's EM protection. For aesthetics, the enclosure can have rounded edges, molded handles, bezels, and be pointed or silk screened.

Traditionally, purchasing large quantities was one way to reduce some costs. Today, modular designs limit the effort, cost, and risk of customized instrument cases. Better yet, a modular design makes customization more cost-effective for prototyping and low-to-medium volumes.