H&E Staining Error Handling System


H&E Staining Instrument (Class II)


Assess existing code base distributed across multiple electro-mechanical modules interconnected over an RS-485 bus and a system application running on a Windows PC.

Design an extensible error handling architecture that effectively addresses disparate fault handling scenarios, complex synchronization, and enable degraded modes of operation to optimize system reliability in the field.


Based on previous work done defining a software architecture that addresses all internal stakeholders' needs, an error handling subsystem using a rule engine architecture was developed in C# integrating well-known off-the-shelf packages to ensure quality from tried and tested solutions.


Developed the error handler as a Windows service on the main Instrument computer, integrating a 3rd party rule engine framework that offers easy configuration management utilities. The framework enables modification to the decision tables directly from Excel, and takes a few simple build steps to build an XML file ready for deployment on the instrument. This offered a big advantage by making multi-discipline collaboration within the development team more efficient, and allowed more concurrent developments with a highly structured system integration methodology. Each subsystem owner (or team) was able to independently tune their subsystem's error handling behavior, which saved significant development time. Also provided was easy service patches for peace of mind; with a few simple build steps, the engineering department can respond to a service request and deploy a minor service patch providing an enhancement without the full administrative overheads of a complete release cycle.

Acceptance testing was conducted on a pre-production hardware platform that demonstrated effective error handling techniques for each failure category. The error handler rule based dictionary provided a high level of flexibility and fine control of error handling behavior at different context levels: component, module, and system. The development team was able to successfully optimize the instrument operations under various degraded states, improving the overall field reliability, while maintaining the safety interlocks.

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