Is my (6514) input keeping a relay energized

[Steve Miket]

I have a 24 VDC fault relay. One side is tied high, and the other side goes to a fault bus. The fault bus is floating, until a path to ground (fault) occurs. Once the fault occurs, the cicuit latches until one breaks the latch by pressing reset.

I'm connecting this fault bus to an input on my 6514 so I can monitor it. When a fault occurs, it appears that the input circuit (through the on board 2.2k resistor) is enough of a path to ground to keep the relay energized (latched). Does this seem right?

Any ideas appreciated, thanks
Steve

[George M.]

Hi,

Is this the behavior you are wanting? If not, how would you like the board to respond? Thanks!

George

[Buechsenschuetz]

I do not think that it is a path to ground. If you have a high level on the input line you have connected the relay to, there will be 2.8 to 5.0V on that line, hence there is a voltage drop of 19 to 22.8V across the relay. Relays rated at 24V will stay energized at a significant lower voltage. If possible, you should try to get data on the 'must open' voltage for that particular relay. This voltage must be higher than the highest possible voltage drop across your input line. But I have severe doubts that there is any relay rated at 24V which is guaranteed to open the contacts at 22.8V.

[Steve Miket]

The desired behavior is that I don't want the input on the 6514 to affect the circuit it's monitoring. However ...

When a fault occurs on the line being monitored, I cannot reset it unless I disconnect the line going to the 6514 input. Then I can reset - so it appears as if there is a path to ground, through that input, that is allowing the relay to stay energized.

Thanks,
Steve