Easy serviceability was one of R. STAHL INDUSTRIAL HMI Systems’ major design goals in developing its Open HMI series of industrial panel pcs. These units enable very comfortable professional maintenance on location, since the enclosure may be opened right within the hazardous area to allow for a selective replacement of specific modules. In a departure from the usual approach, protective measures have been taken on a per module basis for these HMIs. By contrast, conventional explosion-proof panel PCs can often only be completely replaced (if the type of protection is Ex m) or require controlled conditions to be repaired and safely sealed again (e.g. if Ex q protection is employed). Open HMIs, on the other hand, implement the ideal type of protection for every part of a system, permitting use of a light outer main enclosure that requires no special approval. Some few system modules are Ex m protected (inverter encapsulated in a sealing compound), some, e.g. the CPU and power feeder, are Ex d units, connection PCBs are either Ex e or Ex i boards. An Increased Safety (Ex e) terminal cabinet provides ports for connecting hard drives or USB 2.0 flash drives, and also ensures that these mass storage devices can be particularly comfortably replaced. Users who have received some brief training may also take on many service tasks themselves, which greatly facilitates the otherwise complicated handling of explosion-proof devices. Open HMIs are suited for applications in all industry sectors and have received numerous international approvals and certifications. Their open professional software platform makes these devices extremely flexible to use. Last not least, their rugged mechanical design also makes them highly resistant.