Question with Logic

Quick question. See attachment. When sw1 and sw2 is open, why does room light remain off? The light should be on! This happens only when rung 001 is in the program. When rung 001 is removed, then the room light in rung 000 remains on. I am thinking the rung 001 de-energizes the light.

However, when SW 2 is closed the light is on. I dont understand. Any help?

Thanks in advance.

my computer won't open that file ... I suggest you try another method ... maybe press "Print Screen" and then open Windows Paint ... Edit and Paste the screen shot into a new file ... then "Save As" a JPG file ... you should be able to attach that ...

Thanks Ron, new pic uploaded.

this is called a "double coil" arrangement ... the OTE on the top rung is executed with TRUE logic – and tells the PLC processor to "GO WRITE A ONE into the bit/box for the lamp" ...

then ...

the OTE on the second rung is executed with FALSE logic – and tells the PLC processor to "GO WRITE A ZERO into the bit/box for the lamp" ...

then ...

the PLC processor sends the contents of the bit/box (a ZERO) to the output module ... the lamp gets a signal to be OFF ...

did you watch those eleven videos on the "Sample Lesson" page of my website? ... if so, go back and watch them again ... ALL OF THEM IN NUMBER ORDER if you please ... pay particular attention to the STEP I, STEP II, STEP III explanation of the processor's scan sequence ...

I am thinking the rung 001 de-energizes the light.

Click to expand...

that's a beginner's way of expressing what's going on ... secret handshake: the OTE has NOTHING to do with "energizing" or "de-energizing" the lamp (the device in the field) ... instead, the OTE only instructs the PLC processor to either go write a ONE (when executed with TRUE logic) - or to go write a ZERO (when executed with FALSE logic) into the bit/box on the PLC processor's data table ... all of this happens during STEP II of the scan sequence ...

then – later ...

on STEP III of the scan sequence the contents of the bit/box (either a ONE or a ZERO) gets sent to the output module ... THAT'S when the lamp is either energized or de-energized ...

going further:

However, when SW 2 is closed the light is on. I dont understand.

Click to expand...

when SW 2 is closed, the OTE on the second rung is executed with TRUE logic – and tells the PLC processor to "GO WRITE A ONE into the bit/box for the lamp" ...

then ...

the PLC processor sends the contents of the bit/box (a ONE) to the output module ... the lamp gets a signal to be ON ...

many people will say: "in a double-coil situation, the last rung wins" ... there's more to it than that – but you'll hear that saying a lot ...

Thanks Ron, going to your website now.