Radiant energy – Photocells; circuits and apparatus – Signal isolator
Patent
1998-06-04
2000-03-28
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Signal isolator
327 80, 246 28F, H03K 5153, G02B 2700
Patent
active
060435011
DESCRIPTION:
BRIEF SUMMARY
SUBJECT OF THE INVENTION
The present invention relates essentially to a DC input cell intended for data acquisition circuits, more particularly in railway applications.
TECHNICAL BACKGROUND
Currently, DC input cells intended for data acquisition circuits essentially consist of mechanical safety relays which are connected together by simple cabling.
OBJECTS OF THE INVENTION
The present invention aims to provide a cell for DC inputs intended for data acquisition circuits, particularly in railway applications, which has at least equivalent behaviour in terms of safety to that of the prior art, while keeping inherent advantages of compactness, easier maintenance and fitting as well as greater longevity.
More particularly, the present invention aims to provide a cell in which misreading always errs on the side of safety.
The present invention also aims to detect malfunctions which may occur in the various constituent elements of the cell.
The present invention furthermore aims to minimize the influence of a variation in the characteristics of the components which are used, under the effect of an external factor such as a rise in temperature, for example.
PRINCIPLE CHARACTERISTICS OF THE PRESENT INVENTION
The present invention relates essentially to a DC input cell intended for data acquisition circuits, particularly in railway applications, consisting of electronic components and comprising at least two lines of identical elements. Each line is essentially composed of a Zener diode, a switch, preferably produced by an optocoupler, and a second optocoupler comprising an LED diode.
The voltage thresholding is carried out by comparing the input voltage with the reference voltage of the Zener diode, while the DC isolation is provided by the optocouplers.
According to a first embodiment, the two optocouplers comprising the LED diode are arranged in parallel so that data is exchanged between the two lines so as to check the integrity of the system.
According to another preferred embodiment, the two optocouplers are arranged in series head-to-tail, each of them being arranged in parallel with a diode, the two diodes being reverse-biased with respect to the corresponding optocoupler in order to allow current to flow when the corresponding optocoupler is not conducting.
According to a further preferred embodiment, each diode in parallel with an optocoupler comprising the LED diode is replaced by a first resistor, the two first resistors present in each of the lines being strictly identical.
According to a further preferred embodiment, a second Zener diode is provided in each line, where it is arranged in parallel with the first Zener diode followed by the optocoupler fulfilling the function of a switch.
This second Zener diode has the purpose of preventing the reverse voltage of one of the LED diodes of the optocouplers from reaching its minimum breakdown voltage.
According to a further preferred embodiment, a second resistor is placed in series with the optocoupler comprising the LED diode and in parallel with the first resistor, the two second resistors present in each of the lines being also strictly identical.
According to a further preferred embodiment, one of the two lines has a buffer stage with transistor which makes it possible to invert the level of the output impedances, in order to allow the detection of a divergence between the various processing lines in the event that the outputs of the plurality of identical cells are set in parallel by parasitic elements. In this case, this configuration makes it possible to detect a divergence in the event that the various cells are in different states.
BRIEF DESCRIPTION OF THE FIGURES
The present invention will be described in more detail with the aid of the following figures:
FIGS. 1, 2, 3 and 4 represent outline diagrams which show the essential elements constituting a device according to the present invention.
FIG. 5 represents one embodiment of the device according to the present invention implemented by applying the principles described in FIGS. 1 to
REFERENCES:
patent: 4091292 (1978-05-01), Sibley
patent: 4247790 (1981-01-01), Sahasrabudhe et al.
Franckart Jean-Pierre
Husson Henri
Meunier Pierre
Gec Alsthom Acec Transport S.A.
Luu Thanh X
Westin Edward P.
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