Electricity: electrical systems and devices – Control circuits for electromagnetic devices – For relays or solenoids
Patent
1995-12-27
1998-07-21
Fleming, Fritz
Electricity: electrical systems and devices
Control circuits for electromagnetic devices
For relays or solenoids
307326, 361159, G01D 308
Patent
active
057842469
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a safety system provided with separate safety circuits each comprising a semiconductor provided with a control electrode, in whose main path of current a circuit consisting of a coil, a diode and at least one magnetic core winding is incorporated, whereby the main current flows each time when a control pulse is supplied to said control electrode, which main current is interrupted contiguously thereto, as a consequence of which said coil produces a circuit current.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A safety system of this type is known from NL-A-7314056.
The known safety system consists of a safety circuit, wherein a change of the magnetization state of a magnetic core will lead to the control pulse being produced, which control pulse causes a current to flow in the main path of current and the coil, which current is interrupted by the transistor upon termination of the control pulse. The coil will then produce an induction voltage such that the magnetic energy stored therein is released in the form of a circuit current through the diode and the magnetic core winding, which in turn energizes a next magnetic core.
The known safety system is highly insensitive to for example electromagnetic influences from outside, it is reliable and safe to operate, whereby the risk of a current which magnetizes the magnetic core, for example when system components exhibit value fluctuations, short-circuit or are interrupted, being produced spontaneously is extremely small. In order to be able to perform the safety function adequately, it is tested very frequently, for example every millisecond, whether the safety system is still functioning properly by generating a control pulse.
When safety processes, in particular multi-variable processes which are as inter alia used in the chemical industry, for example in cracking plants, on drilling platforms and the like, reliability and operational safety, not only of the installation itself, but also of the safety system, are literally matters of life and death, both for persons and for the environment. Multi-variable processes usually comprise a great many processes and process quantities, which are often connected in a complex manner, and as many parts, which may or may not be controllable, such as valves, regulators, pipes, filters, as well as a many sub-processes, which all require safety measures. Although the above safety system, which functions according to the rules of magnetic logic, is quite reliable, the safety system is becoming more and more extensive as the processes to be safeguarded are becoming more and more extensive, and with it the risk of errors being caused by the safety system itself. Under certain circumstances an incorrect picture of the status and the course of vital process and safety quantities may be given as a result of these errors. It will be apparent that it is unacceptable when the high degree of reliability of the safety system as a whole is affected in this manner.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to reduce the risk of unnoticed errors occurring in the safety system, in particular when processing data which are of vital importance to safety.
In order to accomplish this objective the safety system according to the invention is characterized in that the safety circuits are each provided with a retroaction-free (reaction free) element, which is on the one hand connected to the main path of current of the semiconductor, and which is on the other hand connected to an input of a data acquisition circuit.
The advantage of the safety system according to the invention is that the effect of one class of errors, namely that class of errors where the inherent safety and reliability of the magnetic logic circuits are affected as a consequence of retroaction from (or interaction with) circuits arranged behind the magnetic logic circuit, has been recognized and eliminated. The character
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De Breet Jan Nichlaas
Steinz Hendrik Christiaan
Fleming Fritz
GTI Industrial Automation, Inc.
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