How to check whether a PLC is generating output in response to an input ?

[danishdeshmuk]

How to check whether a PLC is generating output in response to an input ?

I think the PLC electrical drawing should tell this, but if we don't have that page of drawing then what to do to measure & check that PLC is processing the input right & generating the right kind of output of that respective input ?

thanks

 

[chuckey]

First of all, you must know what the output is, it could be serial data,parallel (unusual) or digital (one output goes on), then you need to know what the actual voltages/current capability is , i.e. +5V @1mA, or +12v @.1A, or a short circuit of .5A capability. Once you have a handle on this, build a suitable load (12V battery with a 100 ohm in series...) then apply your inputs and see if the output reacts in the correct way.
Frank

 

[kak111]

First of all you must know how the output is programmed
ie. you need the PLC program list or ladder diagram for checking
under what conditions outputs are turned on and off.
These conditions can be boolean functions between inputs and outputs, timers, counters, registers, etc...

I take a simple example....
Here is a ladder diagram


In first line "Devre 1" right you see output Q3.0




This output is switched on when inputs I0.0 and I0.1 and I0.4 are on
OR Q3.0 and I0.1 and I0.4 are on

ie. boolean function Q3.0 is (I0.0 or Q3.0) and I0.1 and I0.4

Secondly Q3.0 can never be on if I0.1 or I0.4 is not on.

So, if you want to test output Q3.0 you must connect inputs
I0.0 and I0.1 and I0.4 to logic "1", to switch Q3.0 ON.

Connecting I0.0 to logic "0" do not switch Q3.0 OFF
Only connecting I0.1 or I0.4 to logic "0", to switch Q3.0 OFF.

And so on with other outputs.....

 

[munzir]

without going into the program , the electrical drawing of the PLC of that machine won't define the related output of that input ???

 

[kak111]

PLC without the program, does not control the outputs.
Electrical drawing shows only the wiring to terminals on the PLC.

 

[munzir]

Ya i'm only asking about the related output of that particular input .......... Won't electrical drawing show that ??

 

[kak111]

Electrical drawing shows only the PLC wiring .
It will not show in any way, how the inputs are associated with the outputs.

Look ladder diagram in post #3
- Q3.0 is controlled with I0.0 and I0.1 and I0.4
- Q0.0 is controlled with Q3.0
- Q5.0 is controlled with I0.2 and Q3.0
- Q0.1 is controlled with Q5.0 via timer 37
- Q3.2 is controlled with I0.3 and Q3.0
- Q0.2 is controlled with Q3.2 via timer 38