How do I tell the RMC150 to not drive the MDT valves because when Hydraulic Unit is not running?

I noticed when the hydraulic unit is turned off that the RMC150 is still driving the valves at 10v. What’s the easiest way to tell the RMC to not drive the valves?

I use ethenet/ip with an allen-bradley PLC

There are many ways to accomplish this, but they all are fundamentally doing the same thing. What you want to do is take the RMC out of closed-loop control on the axis or axes that are saturating their outputs. I am guessing that the controller is still trying to control position or force, and that the Output Saturated Auto Stop has been set to Status Only.

  • Disable the axis: Have the PLC issue an Enable/Disable Axis (97) command to the axis or axes you want to stop. You will have to re-enable the axes when you want to start up again.

  • Issue an open loop command to the axis: Issuing either an Open Loop Rate (10) or a Direct Output (9) command to the axis with a value of 0 will take the axis out of closed-loop control and set the output to 0 volts. Use the Direct Output command very carefully! The controller ignores the Auto Stops when the Direct Output command is used. The Open Loop Rate command is safer. Just set the voltage ramp to something very high so that the output goes to 0 quickly.

  • Have the PLC fault the controller: This is not a very elegant method, but the PLC can send the Fault Controller (8) command. That will disable all of the outputs, and the controller will not be trying to command the valves to follow a target when there is no oil supply. The controller will have to be put back into RUN mode when the system is ready to start again.

These are just three approaches, there are many other possible solutions with the commands available in the RMC. For example, the Output Saturated Auto Stop could also be set to Open Loop Halt and the axis would then be put into open loop with an output of 0 V when the output saturates. The central idea is that you do not want the controller trying to control position or force in closed loop when the HPU power is off.