Grounding of M for AC500 analog signals
Looking the example of connection diagram below for analog input module AI561 for example, it is shown that the minus of the power supply/module's M terminal have to be connected to the ground.
Is that a must for for minus of the power supply and why so? Is that the protective ground of the cabinet, resp. FE of the controller?
It is strange for me why the power supply potential of 24VDC have to be grounded. Especially when the controller is supplyed from external 220AC/24VDC power supply unit.
IMHO the connection to the PE ground of the system / cabinet of the shield is one good practice to avoid disturbance of electrical signal in input of the controller/CPU.
However all is depending of the real circumstance of the installation, presence of electrical noise in cables or apparatus / devices with possible irradiated disturbances in the nearest.