strain on some portions of the compressor assembly to determine the cylinder pressure the inherent strain caused by the pressure results in a lengthening of the compressor structure and the system described herein measures this change in dimension which is linearly proportional to pressure the system uses similar materials to the compressor so that any thermal expansion effects of increased temperatures are compensated for measuring the strain over a significant length of the structure allows a substantial increase in sensor sensitivity over a strain gauge that may have a relatively low sensitivity multiple sensing systems placed on a cylinder can be summed to add sensitivity and to average any u201c wag u201d in the cylinder that may cause unbalanced strain u201c wag u201d is side to side movement of the cylinder assembly that would cause unequal strain on opposite sides of the chamber there is substantial support and stiffness in the vertical direction but less in the horizontal direction with reference to fig1 an exemplary high pressure reciprocating compressor 10 is shown the compressor 10 includes a compressor frame 12 a pressure chamber 14 and a pressure chamber head 16 a plurality of tie bolts 18 are secured between the compressor frame 12 and the pressure chamber head 16 the use and operation of the compressor 10 are known and details thereof will not be further described with continued reference to fig1 the system includes a rod clamp 20 a sensor clamp 22 a.