Condition-based maintenance, or CBM as it is referred to, is a subset of preventative maintenance. The difference between them is the tools they utilize. Preventative maintenance systems use checklists and OEM recommendations to develop PM routines. The tools that condition-based maintenance use are different.
The common tools used in CBM are oil analysis, heat monitoring, vibration analysis, ultrasonic testing and electric load monitoring. Oil analysis is used to detect foreign materials, excessive heat buildup in the machine and the presence of metals, which indicates machine internal wear.
Thermography is used to sense heat buildup within a machine, a concentration of heat within electrical components, or even abnormalities in roofing systems. Vibration analysis is used to determine the impending failure of bearings or to sense an eccentric load putting stress on equipment. Ultrasonic testing senses sound changes to indicate changes in the operation of a machine. Strip ammeters are used to determine whether more power is being used to operate a piece of equipment than normal. As you can see, there is some possible overlap between some of these tools.