In process automation, consistent “diagnostics" of field devices represent a remarkable potential for savings in the context of operation, maintenance and repair. In addition to process values, intelligent field devices deliver valuable device and process status information, e.g. remaining wear margin, stock of consumables, number of operating hours or process-specific states.
Characteristics and number of device-specific diagnostics typically vary from device to device according to manufacturer, measuring principle and application. Furthermore, with increasing device “intelligence” the number of diagnosis information increases as well. Some may be important for the process operator, other for the maintenance technician only, some for both of them. Operators have to control availability and validity of process values, while the maintenance and service personnel controls correct function of the devices and, if neccessary, locates and replaces defect equipment. Therefore it is considered an important benefit to provide selectively-sorted (role-based) information to the personell concerned and to generally unify the integration of diagnostic signals.
With this in mind and to avaoid a needless overflow of information, NAMUR, the Germany-based process industry end-user association, has published the recommendation NE 107 ("Self-Monitoring and Diagnosis of Field Devices") which requires all diagnostic information provided by the field devices to be categorized into four non-proprietary, unified status categories (fig. 1) in order to provide the user with already pre-sorted information.
NE107 further recommends the association of a diagnostic event to one of these four levels of diagnosis to be configurable by the user according to special needs of his application.
Fig. 1: Meaning and symbols of NAMUR recommendation 107
PROFIBUS diagnostics technology offers an efficient solution to select and send the right information to the right person and thus to avoid an overflow with information and alarms.
PROFIBUS PA devices generally transfer cyclically the value status along with the process value in the form of easy-to-interpret information about the state of the field device and the process. PA devices featuring PA profile 3.02 dispose of a specific mechanism to comply with NE 107 specification as shown in fig. 2. Field devices (A, B, C, …) provide numerous manufacturer-specific detailed diagnostics information (1). This information is mapped already in the field device to the four NE 107 categories (2) by the manufacturer according to his assessment. Consequently, only standardized information is transmitted to the bus system (3). When replacing devices, the owner therefore does not need to spend time or effort on any adaptations or changes of the integrated information. All 3.02 based devices provide identically-structured diagnostic information by default. The categorized information is finally displayed at the control and/or maintenance stations according to the user-specific requirements (4). The mapping to the categories may be changed by the user following the requirements of his application or plant .
Complimentary status information and alarms from the devices are available on request utilizing the acyclic communication channel (5). This information indicates e.g. what device-alarm was activated, where the alarm initiated from, possible reason for the alarm and what corrective actions need to be initiated to restore a normal operating state.
Fig. 2: Diagnostic information mechanism in compliance with NE 107