Programmable logic controllers (PLCs) have very limited diagnostic and no prognostic capabilities, while current smart sensor designs do not have the capability to communicate over Fieldbus networks. The aim is to interface smart sensors with PLCs so that health and status information, such as failure mode identification and measurement tolerance, can be communicated via an industrial Fieldbus such as ControlNet.

The SNE Industrial Fieldbus Interface (SIFI) is an embedded device that acts as a communication module in a networked smart sensor. The purpose is to enable a smart sensor to communicate health and status information to other devices, such as PLCs, via an industrial Fieldbus networking protocol. The SNE (Smart Network Element) is attached to a commercial off-the-shelf Anybus-S interface module through the SIFI. Numerous Anybus-S modules are available, each one designed to interface with a specific Fieldbus. Development of the SIFI focused on communications using the ControlNet protocol, but any of the Anybus-S modules can be used.

The SIFI communicates with the Anybus module via a data buffer and mailbox system on the Anybus module, and supplies power to the module. The Anybus module transmits and receives data on the Fieldbus using the proper protocol. The SIFI is intended to be connected to other existing SNE modules in order to monitor the health and status of a transducer. The SIFI can also monitor aspects of its own health using an onboard watchdog timer and voltage monitors. The SIFI also has the hardware to drive a touchscreen LCD (liquid crystal display) unit for manual configuration and status monitoring.

The SIFI communicates with the Anybus module via a data buffer and mailbox system located on the Anybus module. The SIFI also has headers to connect with the digital and analog SNE modules. A microcontroller is used to control communications with the Anybus module. The microcontroller is capable of processing data either received from or to be transferred to the Anybus module.

Communication is via a parallel interface. The microcontroller is also connected to a real-time clock and 128 kB of external non-volatile FRAM (ferroelectric RAM) memory. For internal diagnostics, the microcontroller is connected to a watchdog timer and is capable of monitoring the levels of the ±12 V and ±10 V voltages.

This work was done by Angel Lucena of Kennedy Space Center; and Matthew Raines, Rebecca Oostdyk, and Carlos Mata of ASRC Aerospace Corporation. KSC-13425

NASA Tech Briefs Magazine

This article first appeared in the December, 2011 issue of NASA Tech Briefs Magazine.

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