Fault detection in relay drive circuits

In a system having at least one output device (21A), the output device having n output terminals, where n=1 to N, for outputting information, and wherein each output device has a corresponding redundant output device (21B), the corresponding redundant output device having corresponding n' output terminals, where n'=1' to N' for outputting information, the n and n' output terminals each being operatively connected to a corresponding m field device (250), where m=1 to N, through an apparatus, such that only the information outputted from one of the corresponding n and n' output terminals is coupled to the corresponding field device m, said apparatus comprising:

• a) at least one fist current source means (211A) for outputting a current, each first current source means being connected to the corresponding output terminal (n) of the output device (21A), the current outputted from each first current source means containing the information outputted from each corresponding output terminal (n) of the output device (21A);
• b) at least one second current source means (211B) for outputting a current, each second current source means being connected to the corresponding output terminal (n') of the corresponding redundant output device (21B), the current outputted from each second current source means containing the information outputted from each corresponding output terminal (n') of the redundant output device (21B);
• c) at least one first diode (212A), each first diode connected to the corresponding first current source means (211A) and to corresponding first connector terminals (11A), and further wherein each connection between the first diode and the corresponding first current source means are each connected to corresponding second connector terminals (12A);
• d) at least one second diode (212B), each second diode connected to the corresponding second current source means (211B) and to corresponding first redundant connector terminals (11B), and further wherein each connection between the second diode and the corresponding second current source means are each connected to corresponding second redundant connector terminals (12B), and further wherein each first redundant connector terminal (11B) is connected to the corresponding first connector terminal (11A), and further connected to the corresponding field device (250-1, 250-2, . . . , 250-8), thereby providing a path for coupling information from the output terminals (n) of the output device and the output terminals (n') of the redundant output device to the corresponding field devices;
• e) at least one switching means (253) for switching, the number of switching means being from 1 to n, each switching means having corresponding n first contact points (256) and n second contact points (257), each second connector terminals (12A, 22A, . . . 82A), being connected to corresponding first contact points (256-1, 256-2, . . . , 256-8), and each second redundant connector terminals (12B, 22B, . . . 82B) being connected to corresponding second contact points (257-1, 257-2, . . . 257-8);
• and
• f) activating means (254), operatively connected to the output device (21A) and the redundant output device (21B), for activating each switching means in response to control signals, control signal A and control signal B, CONTA and CONTB, respectively, from the output device and the redundant output device, such that the information outputted from the output terminals of the output device or the information outputted from the output terminals of the redundant output device is caused to be bypassed by the switching means resulting in the unbypassed information being coupled to the corresponding field device.