I am an industrial electrician with basic electronic knowledge, i have just finished building and fitting a control panel for a production line. I used some of the transistor outputs (PNP) on the invertor for alarm indicators, this involved 3 terminals" live in", "switched live out" to load and "0v" which was commonod to the load negative. This makes sense and worked fine, but when i wired the output transistors of the Mitsi PLC in the same panel i only had to connect 2 terminals a "live in "and "live out" to the load, with only one 0v feed direct to the load negative. I wondered how the PLC transistor worked without a 0v connection, i.e where does the base current flow or it it grounded through the load to negative. I am mainly used to relay outputs so any advice would be appreciated......Thanks

 

The control signals to the internal relays of the PLC are connected internally.

 

Thanks but these are Transistor outputs or it it still the same thing?

 

What inside is protected, no more diagrams,just input and out put. You may get a member to help more,post all part info and what it is used for.There are members that can give you a good idea of what going on to your satisfaction.Post pictures
will help.

 

Thanks but these are Transistor outputs or it it still the same thing?

It is the same thing. The control signal are inside and you only have access to the part of the transistor which contacts current as to switch on/off relays etc.