A portable electronic system for in-situ measurements of oil concentration in MetalWorking fluids

• An instrument is presented to measure oil concentration in MetalWorking fluids.
• The instrument is portable and battery-operated.
• The instrument is based on the falling ball principle of viscosity measurement.
• The sphere fall time is determined with a couple of inductive proximity sensors.
• A good linear correlation is found between fall time and oil concentration.

MetalWorking fluids (MWFs) are widely used to cool and lubricate machines and tools. By far, the most common MWFs are oil-in-water emulsions with oil concentration (Coil) in the range from 1% to 10%, depending on type of oil, material to be worked, etc. In order to optimize emulsion and machine performance, as well as for good waste policy, the right value of Coil should be kept (approximately) constant during the MWF’s lifecycle to compensate inevitable changes due to water evaporation, bacterial attack, oil adhesion to metal parts, etc. This, however, requires periodic measurements, often skipped because they require unhandy operations and produce inaccurate results. In this context, a new system is presented that is based on the falling ball principle, normally used for viscosity measurements, shown to be suitable also for accurate Coil measurements. In our system, the transit time of the sphere within the instrument is determined by means of inductive proximity sensors, a PT100 sensor is used for temperature whose effects on Coil are accounted for by means of an ad-hoc algorithm. A battery-operated electronic board has been designed that allows rapid and user-friendly “in-situ” measurements and a prototype of an whole portable and automatic instrument, suitable for in-situ measurements, has been fabricated.