There are various types of food machinery, and their working conditions are different, so the faults of different mechanical equipment often need to be diagnosed by different methods. The methods of fault diagnosis of mechanical equipment can be classified in the following ways.

Classification according to the purpose and requirements of diagnosis

1. Functional and operational diagnostics
Function diagnosis is to diagnose whether the function of the newly installed or just repaired mechanical system is normal, that is, the diagnosis before it is put into operation. The operation diagnosis is aimed at the normal working mechanical system, and it is necessary to monitor the occurrence and development of its faults.

2. Periodic diagnostics and continuous monitoring
Periodic diagnosis is a routine inspection of the mechanical system in working condition at regular intervals, such as 1 month or several months. Continuous monitoring is the use of instruments and computer information processing systems to continuously monitor or control the operating status of the mechanical system. The use of the two diagnostic methods depends on the criticality of the equipment, the severity of the impact of equipment accidents, the speed of performance degradation during operation, and the predictability of the occurrence and development of equipment failures.

3. Direct and indirect diagnosis
Direct diagnosis is the direct determination of the condition of critical components such as main bearing clearance, gear tooth flank wear, and pipe wall thickness in corrosive environments. If the direct diagnosis cannot be realized due to the limitation of mechanical structure and working conditions, indirect diagnosis must be used.
The so-called indirect diagnosis is to indirectly judge the state changes of the key components of the mechanical system through the secondary diagnosis information. Most of the secondary diagnosis information belongs to comprehensive information, such as using the lubricating oil temperature rise to reflect the running state of the main bearing, and judging whether the gears in the gearbox are normal by measuring the vibration of the box. The possibility of misdiagnosis and missed detection in the secondary diagnosis will increase.