sinking and sourcing

[BenPLC]

I am making a training board for an FX1N series PLC. I have DC lamps (1 wired to ground, and 1 to each output (indirectly), Y0 thru Y17. The common is connected to 24V. What should the S/S (sinking or sourcing) terminal be wired to? (24 or 0 V)? Since I had a limited availability of supplies, It required a little more work. I've ued 12v lamps connected to 12v voltage regulators(3 terminal type) in conjunction with the 24VDC power supply. 1-input 2-ground 3-output. I have wired the outputs to terminal 1 above. Terminal 3 is wired to the lamp. Again, what should the S/S terminal be wired to? and should it matter that I'm using voltage regulators? Thanks Ben

[waynes]

Hi BenPLC, the s/s terminal is connected to 0V if your inputs' 'hi' level is about 24V(Source). If your are using sink input (0V), your S/S will be connected to 24V.

[Sergei Troizky]

The S/S terminal defines the inputs polarity and has nothing with the outputs polarity which is strictly determined for certain type PLC or extension unit. By conecting S/S to +24V, the inputs are configured for sinking signals (NPN sensors). By conecting S/S to common, the inputs are configured for sourcing signals (PNP sensors). If left unconected, the inputs will not operate.

[BenPLC]

Thanks for your reply- Does it matter if I use s/s 0V or s/s 24V? That is separate from the common output right? For this application, I don't have any sensors(NPN/PNP)--- only toggle switches. Thanks again

[panic mode]

S/S is just for inputs and you wire it to provide path (complete circuit). So if sensor is providing +24V, S/S should be connected to the negative (and vice versa). Check PLC documentation for grouping of I/O. Outputs will have separate common(s). What type of lamps you are driving? If they are LEDs (low current), just use resistor in series. If they are incadescant, your 3-pin positive regulators will get very hot very quickly (is this 7812 or clone by any chance? if so your wiring is correct but linear regulators are not efficent, you might want to replace regulator with just another lamp). Better way is to match power supply and load...

[Colin Carpenter]

Just to say that I left the S/S terminal unconnected once and saw the wierdest things happen!! Inputs were coming on as and when they felt like it, including those that weren't even wired up. You have to make a choice and wire it ..... leaving it unwired is NOT an option.

[BenPLC]

Thanks- I will wait and buy 24VDC lamps next time. Yes, the regulators are 7812.

[Sergei Troizky]

Correct. I should say "inputs will not operate correctly".

[sid]

Instead of using regulators at the output of PLC you can connect the input of regulator to 24VDC and output to the common of the PLC. So now you can connect your lamps directly to the output of plc i.e plc now switches 12V at the output.