Unable to read Digital output (DO) from a robot Controller with a PLC (DL205)

[JerryH]

OK, I see it now. I didn't see that the Common on the PLC input was tied to +24.

If you take a jumper and tie a PLC input to the minus side of your 24v power does the input come on then?

 

[bernie_carlton]

You are supplying the 24VDC through the LED section of the input module.

 

[latendal]

@Jerry I do read the input signal in ladder logic when that input port is connected to the -ve terminal of my power supply!

@Bernie Are you pointing something out I've done wrong!?

 

[bernie_carlton]

Except for your perceived need for a resistor I wasn't pointing to any error. Your diagram, as drawn, should work.

 

[latendal]

Except for your perceived need for a resistor I wasn't pointing to any error. Your diagram, as drawn, should work.

Ah! Sorry! i realize my sketch can be confusing but the 4.8k resistor on the sketch is the internal resistor in the PLC input module

 

[bernie_carlton]

Well, ok then. Maybe consider bad cable or breakout board. I've seen it.

Just to review then. If your measure near zero VDC between COM and the PLC Input at the ZipLink breakout board (Robot output transistor is OFF) the PLC input (as seen in the program) should be OFF. When you measure approx 24 VDC between the same points (Robot transistor is ON) your PLC input should be seen as ON.

 

[latendal]

Well, ok then. Maybe consider bad cable or breakout board. I've seen it.

Just to review then. If your measure near zero VDC between COM and the PLC Input at the ZipLink breakout board (Robot output transistor is OFF) the PLC input (as seen in the program) should be OFF. When you measure approx 24 VDC between the same points (Robot transistor is ON) your PLC input should be seen as ON.

uhmmm! I believe i measure 0V because both plc input and com are at 24V (due to incomplete circuit) and which explains why i read 24V between either points and power supply -ve terminal. For PLC to be on i'd have to read 0V or near 0V between plc input and -ve terminal or 24V between COM of PLC and plc input which i haven't achieved yet unless in the instance when i connected the -ve terminal of my power supply directly to the PLC input with the purpose of verifying my PLC input wasn't fried (turns out its in good condition)