Automatic determination of trigger angle for reciprocating compressor rod drop measurements

A machine monitoring system for acquiring information regarding operation of a machine having a piston rod and a rotating component to which the piston rod is connected, the system comprising:

• a rod position sensor mounted adjacent to the piston rod, the rod position sensor generating a rod position voltage signal indicative of proximity of the piston rod relative to the rod position sensor during operation of the machine;
• and
• a rod position monitor circuit in communication with the rod position sensor, the rod position monitor circuit comprising:
• one or more analog-to-digital converters for sampling the rod position voltage signal and for converting the rod position voltage signal to digital rod position data;
• and
• a processor operable to execute operational instructions for processing the digital rod position data, the operational instructions comprising instructions which, when executed:
• determine a rotational speed of the rotating component of the machine;
• detect a full rotation of the rotating component of the machine;
• determine a plurality of slope values of the rod position voltage signal based on the digital rod position data, wherein the slope values are calculated on a sample-by-sample basis during the full rotation of the rotating component, each slope value indicating a slope of the rod position voltage signal between adjacent data samples;
• within the plurality of slope values, find slope values that are consecutive in time and have amplitudes that are within a predetermined amplitude range about zero slope;
• determine a time range during the full rotation of the rotating component having the most slope values that are consecutive in time and have amplitudes that are within the predetermined amplitude range about zero slope;
• determine a rotation angle of the rotating component corresponding to the time range;
• and
• calculate a trigger angle based on the rotation angle according to:
• trigger angle=rotation angle+piston angle,
• wherein the piston angle is a predetermined stored value;
• and
• memory for storing a trigger angle configuration value corresponding to the trigger angle calculated by the processor.