Abstract
The philosophy is presented of multiple binary measurement, an approach capable of providing simultaneously the desiderata of ‘self-validation’, ‘fail-safe’ and ‘fail-operative’. The systems described continually examine the validity of their outputs such that any measurement malfunction causing an error greater than a predetermined and insignificant value automatically raises an alarm.
The systems use a series of binary measurements, each individually derived and each arranged to operate at a small increment of the chosen parameter above the previous measurement: the value of one increment thus represents the maximum tolerance of an instrument. Maloperation of any one binary channel will cause an alarm, either immediately or when the parameter reaches that value dependent on its position in the sequence, to proclaim that it is telling a lie. This applies for either direction of failure, and in conjunction with a suitable display the error is located while the other portions continue their functions unimpaired.
A reference is included of the Hydrastep boiler water level gauge, which has received statutory approval in the UK as a sole gauge for high-pressure boilers, and is one example of a group of instruments conforming to this philosophy.
Get full access to this article
View all access options for this article.