Issues using BT50 relays with AC500-S DX581-S I/O module
We are attempting to use BT50 safety relays, controlled by a digital output of a DX581-S safety I/O module in an AC500-S PLC system.
The issue we are having is that the digital output from the DX581-S fails to activate the BT50 relay. Specifically, the "On" and "X4" LEDs are lit, but the "Out" LED is not lit. In this case, the voltage over the relay is 23.74V and the current to the relay is 40 mA.
The connection of the BT50 safety relay is verified as correct. We have verified this by connecting the relay directly to our +24V power supply instead of the activated DO channel on the DX581-S module. This activates the relay properly.
We have verified that this is not dependent on the specific relay unit (behavior was identical on 6 different BT50 relays) and not dependent on the specific DX581-S I/O module or terminal base (behavior was identical for 2 separate AC500 PLC systems).
We have verified that the DO channel can be sufficient to maintain an activated relay (23.74V, 60 mA, "Out" LED lit). If the power supply connection is used to trigger the relay, the relay remains active even if that connection is broken, as long as the DO channel is active. If the DO channel is cycled (turned off and on again), we revert back to the failed activation state (23.74V, 40 mA, "Out" LED not lit).
Does anyone have an idea of why this may be? Has anyone had similar experiences with these, or other similar, components? If so, did you manage to solve it?