IEC TS 62098:2000 pdf download

IEC TS 62098:2000 pdf download.Evaluation methods for microprocessor-
based instruments.
2 Developments In Instrumentation
Instrument functions can be realised in various ways.
In analogue Instruments, functions are realised by the layout and size of hardware components and by the use of analogue data processing.
The first instruments equipped with microprocessors and using digital data processing techniques appeared in the late 1970s and early 198Os Since then, the use of software-based digital data processing techniques for measuring instruments and controllers has grown disproportionally. Also there has been an increase in functionality and data processing capacity.
Microprocessor-based nstruments are sampled data systems. That means that the outputs and other relevant data are refreshed or updated with new data at certain time Intervals or cycle times. Besides the measurement task, the instrument has in the same operating interval to perform other tasks such as communication and self-testing. In particular, for time- dependent functions (control, integration, etc.) microprocessor-based instruments can become time-critical. This means that errors can appear when time-housekeeping is either inaccurate or disturbed. Time-housekeeping can for instance be upset when the design allows simultaneous operation of various tasks without a careful prioritisation in the multi-tasking.
The extensive data processing, memory and storage capabilities of microprocessors permit the integration of control algorithms (e.g. PID) and process trend information in measuring instruments.
The data processing capabilities also permit the use of more complex sensing techniques. They have provided opportunities to develop more exotic” types of sensors where the measuring principle needs for instance the use of statistical methods to determine the physical quantity.
Increased knowledge of sensors has led to better mapping of the sensor characteristics, These maps can be embedded in the software, and by the use for instance of internal auxiliary sensors they can be used to provide a much greater rangeability such as in pressure and differential pressure sensors,
Moreover, the processing capacity provides the possibility of processing sensor data to derive other information that can be of Interest for maintenance purposes, Maintenance may also be supported by auxiliary sensors that provide Information on wear-out or overloading etc. of the instrument or the equipment to which it is connected. Stored historic, diagnostic and statistical data may also be used for improving maintenance.
The communication interface may be designed for communication with a high-level operator interface over a digital communication link. It may also allow direci instrument-to-instrument communication over the same link.
Some of the above-mentioned considerations are summarised in table 1.
Using this definition, every instrument can be treated as a system.
An ideal system (the concept) should be able to indefinitely perform its function without error. fault, failure and unwanted delay. However, the real system developed from the functional concepts is not ideal due to the imperfect (time- and space-bound) nature of the materials used. It is therefore sensitive to disturbing external factors.
Because of this non-ideal behaviour of the real system, there is a practical need for characterising the points of concern with respect to their application in more or less measurable properties, such as accuracy, stability, reliability, maintainability, etc.
The specifications of the properties indicate the deviations between the functional concepts and the real isation of the functions of a system and are a measure of its quality.
The main constituents of a system described above and the interaction with the environment are clearly shown in figure 1. The environment is for practical reasons further split into a number of domains The boundary is expanded to a boundary area consisting of a number of interfaces. The various environmental domains are the sources of disturbance (influencing conditions) for an instrument.
3.2
Evaluation matrix
The main points to be defined in detail for an evaluation are:
a) instrument elements;
b) instrument functions;
C) instrument properties;
d) influencing conditions.