For stand-alone measurement-and-display in Hazardous Locations, an MDI and MPI greatly simplify both the amount of equipment needed and the installation procedures. The battery-powered MDI display is not only rated for installation in Class I, Zone 1 areas, it is also rated to power a single Intrinsically Safe device installed in Class I, Zone 1 or 0 areas without the need for complex IS barriers or explosion-proof conduit. Similarly, a single MPI probe can be installed in a Class I, Division 1 or Class I, Zone 0 location and connected directly to an MDI display.
In more complicated scenarios, an MDI display with an auxiliary connection can be used with a passive monitoring system to provide system-wide access to the readings from the MPI probe. While a barrier is not required between the MDI display and MPI level probe, an Intrinsically Safe barrier is required between the MDI display and the external monitoring system. The external system can only passively read the MDI display. However, the external system can be set to provide a “Wake Up” input to the MDI display, preserving the life of the battery powering both the MDI display and the MPI probe.