Protection
Measurement Types
2 - 12
SKF Multilog On-Line System IMx-M
User Manual
Piston Rod Drop
The piston rod drop measurement is provided for the purpose of monitoring the piston
rider band wear to prevent the piston from contacting the cylinder liner.
The piston rod drop measuring system is not only affected by rider band wear but all
piston rod movements. The cause of the movements could also be one or more of the
following:
Rod mechanical runout due to crosshead-to-cylinder misalignment in the
measurement plane.
Cross head play / wear
Rod deflection.
Forces imposed by load and process condition changes.
All these factors occur to varying extents in all reciprocating machines and will affect the
measurement which could lead to wrong conclusions regarding the rider band wear,
especially so when Average Mode is used.
Single channel measurements can be configured as well as measurements of two
primary channels combined into an X-Y-measurement.
Figure 2 - 8.
Piston Rod Drop Configuration.
There are sensors measuring the position of the piston rod and a tacho sensor which is
used to measure the rotation speed but also providing the zero degree reference point.
The tacho sensor must deliver only one pulse per revolution.
The position measuring has no filters other than a hardware input low pass filter.
Piston Rod Drop Physical Properties
Start angle and Stop angle
The Start angle and Stop angle are configured in degrees relative to the trigger
point. They specify the part of the revolution at which the measurement will be
based. Start and stop angles close to the end of the revolution should be
avoided. See "Measurement Angle" and "Measurement Angles and Non
Constant Speed" in
