No voltage at outputs even when forced

[Greenhorn 0]

 I am very green at this and learning online as I have purchased a brand new Micrologix 1400 1766L32BXBA. I am pulling my hair out as I cannot even power an LED or for that matter get any 24 volt reading from the outputs via program. I have even forced them on so shouldnt I be able to see something? I am connected via Ethernet ,Rslinx in concert with using Micro starter software (not lite) and the unit does not show any faults and is in the run mode. I can see the bits forced on the software and on the unit's LCD screen in I/O status. Is there a way to trouble shoot if the unit is bad or I am overlooking something incredibly simple. I do not have any floating inputs or outputs with the common from the power supply and the unit is properly grounded all nice and tidy on a din rail. Like I said I am very new at this so I am sorry if this is a bad question.

[ElectronGuru 81]

The power supply in a Logix device (whether ControlLogix, CompactLogix, SLC, or MicroLogix controllers) supplies power only to the cards in the chassis backplane, or the I/O modules (if added on expandable units) on a Compact- or MicroLogix bus. Power for the field devices must be wired from a separate, external power supply. Remember that digital outputs in any Logix controller are just optically isolated "relays" to conduct power from an external power supply to a field device. When an physical output is on (true in the logic or force table) you should get an LED indicator on the associated Logix module output status indicator. If you're getting that LED saying you should have an output, that means connectivity is established between the field power supply and the filed device, same as if closing a normally open contact on a relay. So, make sure you have an external field power supply properly wired to your MicroLogix controller and the field device(s).

If you have a field device power supply properly wired, it's power is on, and you're getting the LED status indicator on the PLC's output, you need to check your I/O module and field device to make sure they're matched for sinking and sourcing. Not going to get into that here, but check the manual in this attached link, chapter 3:

https://literature.rockwellautomation.com/idc/groups/literature/documents/um/1766-um001_-en-p.pdf

If the field power supply is wired correctly, the LED status indicator on the PLC's output is on, your field device and PLC are matched for sink/source, and you're still not getting the output, the output itself may be bad. In ControlLogix chassis we can disable an I/O card but I'm not sure if that's true in the Micro-1400. Again, check the manual.

Hope this helps.

[Greenhorn 0]

Thanks for replying. The micrologix 1400 can be expandable but it has a 24 volt power supply to power relays in the field and I am just powering a field device simulator toggles, led pushbuttons for Input and Output which I know it can do. Its part of an online class I am doing. My problem is the leds in the push buttons wont even light up and looking further the lugs them selves do not have a voltage present. I tried forcing them all on and take readings but to no avail. I think I am going to return it for an exchange.

[ElectronGuru 81]

What specific model of 1400 do you have?

[ElectronGuru 81]

And, can you supply a pic or drawing of your wiring?

[alan_505 24]

Are you writing your logic in ladder 2 or another ladder, if it is in another ladder then you will need to put a JSR(Jump to Subroutine) in ladder 2.

By default ladder 2 is the only one scanned when the PLC is in run mode.

[pturmel 157]

The 24V power for the unit is not internally connected to the output rail.

Show how you actually wired it.

[panic mode 246]

yup... probably incorrect wiring. have not use ML in very long time but was helping students with their project and had to try explaining the outputs and wiring a bit more. here is adapted version.

Some ML have mixed outputs. LX32BXBA seem to be one of them. Also all outputs need to be powered - from outside. 

Relay outputs are easy to understand, the relay contact is acting just like a switch. And even newbies should not find it hard to understand that every switch needs one side connected to the power and the other connected to the load... And both switch and relay contact will happily handle either AC or DC (within limits, always check specs). And because simple switch (and relay contacts) are not polarized, you can also place the switch (or relay output) in the negative leg of a DC circuit if you want. 

To reduce number of termination points, it is very common that inputs and outputs are internally grouped (bussed, ganged) so that single terminal can be used as "common". But this limits options when working with circuits that are galvanically isolated. So to make things more flexible, not all outputs are grouped all together. They may be split into smaller groups so that one can mix and match different loads (AC or DC, positive or negative). In case of L32BXBA, there are four individual outputs (OUT0, OUT1, OUT 8 and OUT 9). Another two relay outputs are OUT10 and OUT11. They are grouped together (they use same supply via terminal DC5/VAC).

Transistors outputs are a bit different. Slightly... 

They are polarized so one cannot do all of things that we just described with relay outputs. Also (in general) transistor outputs are rated for less current when compared to relay outputs. But they can be FAST, their signal is CLEAN (no bounce, suitable for pulse trains for example), they can last virtually forever (no arcing and degradation due contact oxidation) and they are much smaller (easier to get a lot of them in tiny package).

in Case of L32BXBA all six transistor outputs are grouped together (they use same supply VDC2 is positive and COM2 is negative). Reason for two terminals for power is that (unlike relay outputs), transistor are 3 terminal devices so input and output are not galvanically isolated. Therefore outputs have driver logic that is powered from same circuit that the outputs are controlling. This means they need negative terminal as well. And since positive is already present anyway (in this case VDC2), there is a terminal to bring the negative supply too (COM2). Without connecting both, those six outputs are NOT going to work.

Finally, I am really not fan of the silly and completely abstract illustrations that this manual uses. So I tried to indicate internal circuitry (relay contacts and transistor outputs). This should help with understanding polarity and easily differentiate the output types. If you are using all outputs to drive DC loads, you may wire them like this:

[Greenhorn 0]

THANK YOU

Well that solved my problem that never existed. It was my wiring as I did not apply power to the dc output groups. I feel like a doofus but at the same time pretty dang happy. Thanx to everyone here. I saw this diagram and the first thing that popped into my mind was "of course" what was I thinking, I was not. I jumpered all of the 24vdc on the dc outputs I am using and wah lah. Again, thanx alot gentlemen!

[pturmel 157]

You'll have to change your moniker now.  You're no longer a Greenhorn. 

[panic mode 246]

very good, now show that PLC who is the boss...