Microlok is a vital microprocessor-based railroad signal control system. It is commonly used to control interlockings, signals, switches, track circuits, routes, and other railroad signal functions.
Microlok programming is used to create the logic that tells the system how the signal equipment should operate safely under different field conditions.
Microlok programming is considered vital because it directly affects safe train movement. The logic must prevent unsafe conditions such as conflicting routes, improper signal clearing, or switch movement under a train.
Microlok programming is performed using proprietary software and a special programming language developed for railroad signal applications.
The original Microlok system was developed by GRS, which later became part of Wabtec. Because the system is safety-critical, access to the programming tools and detailed logic is controlled.
The Microlok programming language is designed around railroad signal concepts. It allows engineers to build logic using ideas such as track occupancy, signal aspects, switch correspondence, route locking, approach locking, time locking, and traffic direction.
Engineers use the Microlok development environment to write, check, simulate, compile, and prepare the logic for installation into the field unit.
Before the program is placed into service, it must be reviewed, tested, verified, and approved according to railroad safety procedures.
Microlok logic can be tested before being placed in service. Simulation helps engineers confirm that routes lock correctly, signals clear only when conditions are safe, and field inputs and outputs respond properly.
After testing and approval, the compiled program is installed into the Microlok unit. Field testing is then performed to verify that the programmed logic matches the plans and operates safely with the actual equipment.
Other signal manufacturers also use proprietary vital logic systems. Examples include Siemens, Alstom, Wabtec, and other railroad signal equipment manufacturers.