Improved transducer design for machinewear debris monitoring

In recent years several systems have been reported which use coils placed close to the lubricant flow in a machine to monitor the presence of metallic wear debris. Operation is based on changes in coil inductance caused by metallic debris in the coil. Unfortunately, any air bubbles or water droplets in the lubricant stream will modify the stray capacitance of the coil, leading to false indications. The purpose of the Letter is to describe a method of coil construction that overcomes the problem of bubbles being detected as metallic debris.