Pressure sensor

Resistance welding apparatus comprising a piston having opposing faces for applying welding electrodes to a workpiece, means for measuring a pressure ratio across opposing faces of the piston and means for controlling the supply of welding current to the electrodes in dependence on the pressure ratio.

A pressure sensor for resistance welding apparatus, the sensor comprising a piston having a first face and an oppositely-directed second face larger than the first face, means for applying to the first face pressure fluid utilised to effect closing movement of electrodes of the welding apparatus to apply a welding force to a workpiece, means for applying to the second face pressure fluid being vented to permit such electrode movement, the relative areas of the first and second faces being chosen such that the force exerted by pressure fluid applied to the first face exceeds the force exerted by the pressure fluid acting on the second face when the welding force applied to the workpiece is a predetermined proportion of a maximum value, and means for controlling an electrical signal in response to movement of the piston resulting from the difference in forces applied to its first and second faces.

A method, apparatus or sensor, substantially as herein described with reference to, or as illustrated in the accompanying drawings.