For circulating lubrication systems with filtration devices (eg hydraulic systems, turbine units), the optimum sampling point is in the return line; if it is to be judged that the equipment is worn, it should be sampled before the filter return line filter; if the filter is to be evaluated The filtering effect requires sampling both the front of the filter and the back of the filter;

For oil bath lubricated equipment (eg gearboxes), the best sampling position is in the middle of the tank. If the tank is equipped with a sampling valve, it can be sampled at the sampling valve. Samples should be avoided at the bottom of the tank to avoid excessive deposits affecting the estimation and evaluation of the operating conditions of the equipment.

During the monitoring process, each sampling point should be consistent and a special sampling device and vial should be used to ensure that the oil is not contaminated during the sampling process.