Analog output connection

[Ivan Ristic]

Hello. This is my first post to this forum.

I've been using Unitronics PLC for couple of the projects in the past and now I need help regarding hardware connection of analog output module. Currently I am just planning for the next project, so I don't have any hardware yet.

I need to control the speed of 10 frequency drives so idea is to use two analog output modules UIA-0006 configured as 0-10V. Common point of analog inputs on all VFD's will be connected to 0V system power supply. This power supply will be used also to provide power for all IO modules in the system and PLC with HMI itself.

Question is do I need to connect common ground (CM0, CM1, CM2, CM3, CM4 and CM5) to system 0V or leave it unconnected and just use voltage outputs (O0V, O1V . . .) connected to VFD analog input? I am asking this because in the manual it says that analog outputs are not isolated, so I assume that internally all common points are connected to 0V power terminal.

In the manual for UIA-0006 there is also two sentences which are not clear to me:

• Individually connect each 0V point and each common (CM) point in the system to the power supply 0V terminal, unless otherwise specified (page 5).
• Do not connect the common point (CM) to the 0V point (page 6).

Is there any risk of damaging UIA-0006 with this connection? Even if I disconnect common points on VFD's they will probably still be connected through analog output module because outputs are not isolated.

Thank you for help.