A method of monitoring a fluid process control system having a control loop for controlling the flow of a material through a path in the fluid process control system. The control loop a control valve, a valve controller, and a fluid control line. The control valve is disposed in the path and is movable between an open position and a closed position. The valve controller is for controlling movement of the control valve. And, the fluid control line couples the valve controller to the control valve. The method detects a first pressure in the control loop with a first pressure sensor. Then, a second pressure can be detected at a location that is external to the control loop with a second pressure sensor. Finally, the method can include determining a characteristic of the control loop based on the first pressure.