A method and a control system for a refiner for pulp or like materials, the control system (100) comprising a sensor (90) mounted in direct mechanical connection to a non-rotating refining member (26) so that the sensor is responsive to axial vibration movement of the support (12), and an analog to digital converter (96) connected to the output of the sensor (90). The method and control system also include a controller (97) connected to the analog to digital converter (96) and responsive to the analog to digital converter to compare the amplitude of the output signal (90) from the sensor to a baseline value based on the level of vibration associated with the pulp refiner when it is operating without plate clashing. When the signal exceeds the baseline value, an action is taken to help alleviate the plate clashing.