I second, Jonathan's recommendation.
The device he suggested is a current switch and it can be connected to a PLC input. The output of the DCS will close (go active) when the DC current is greater than the set point.
Please note that the minimum current that the DCS100 can detect is 5A DC. You want to sense 1A DC. You will need to loop the wire that you are trying to sense several through the "eye" of the current sensor several times so that when 1 A is flowing through the wire, the sensor will think that 5 or more A is flowing.
Automation Direct also offers the DCT100 current transducer that can work with the FDM88 analog inputs. If you need to measure current and not just have a on/off indication, then a current is what you want.
Gary D.