Importance

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Abstract

A method and apparatus for generating a current corresponding to a quantity supplied to the device, for example an analog current output device for a digitally working process control system, using two parallel-working current-generating means, each one connected to a current summation means; the current-generating means are each adapted to generate a current proportional to the quantity and the proportionality being determined by a changeable proportionality factor. Each one of the current-generating means being adapted to supervise both its own function and that of the other means. Upon indication of a malfunction in one of the means, the function of the device is taken over by the other means alone. Each one of the current-generating means may preferably be adapted, by means of switching means, to close an alternative circuit for the generated current for sensing whether an indicated malfunction in one of the current-generating means is caused by an internal fault in the current-generating means or by an external fault such as an interruption in the part of the circuit which is connected to the means, for the generated current.

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First Claim