How to hook up MicroLogix 1100 FET discrete output

[drbitboy]

Are the red and black wires in the image below the right way to drive a 0V or 24V discrete output signal from a O:0.0/2 of a MicroLogix 1100?

Also, do I have the right behavior described for the voltage at the blue x?

If yes to both, then I am pretty sure this is a sourcing output. Do I have that right?

I realize the design of the load will also need to limit the current, but I am more interested in getting the wiring right for now. Also, I realize that 0V and 24V are nominal, and the actual signals might not be exactly those levels because O:0/2 uses a FET.

The base diagram is from the ML1100 Installation Manual here.

I understand Ohm's law reasonably well, but I am definitely weak when it comes to terminology and jargon of DC. After a while I finally realized (I hope) that "DC 24V-" is an alternate expression for "COMmon" i.e. the low side of a 24V range, and is not the same as "DC -24V" i.e. a voltage 24V below a ground level voltage.

There is an old thread about a similar task here. The OP in that thread mentioned connecting the COM and the GND, but I am guessing it would also work if the DC 24V- IN and the O/2-O/5 "DC 24-" (DCc) were isolated from the ground (⏚).

Sorry for the basic questions, but I could not find anything that laid it out like that: the base diagram does not show +DC IN and -DC IN connected to +DCc and -DCc, respectively. That is probably obvious to everyone, and they are not connected in the base diagram because the designer may want to supply an external voltage source to +DCc and -DCc, but it was not obvious to me.

Thanks.

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[parky]

All looks good to me, it is basically the same as transistor output units, I also agree with connecting the V- to the ground all the panels I have built I do this.
However, I would put in a breaker or fuse feeding the output supply the PSU will probably be something like 4-10amp depending on your supply requirements so perhaps a smaller fuse/breaker feeding the +V common of the outputs to protect them from shorts. Some people fuse the outputs individually but that is a matter of choice.

 

[Saffa]

Yeah looks fine to me, Parky's comment about fusing is a valid one even for testing, very easy to accidentally cook something and those FET outputs are sensitive (I've blown a couple on a 1400 once by not paying attention ).

24V comes out of the output terminal for logic state 1, as you've drawn.

What kind of load are you driving?

 

[drbitboy]

Thanks @parky, @Saffa. I mainly want to avoid letting the magic smoke out.

It's for my home lab: the power supply is the charger of a defunct laptop. I am hoping to drive this servo via PWM.

That fuse is a great idea; thanks for that too. As you are probably aware I am usually programming with internal bits (B3/n) as proxies modeling real I/O; moving external electrons requires a different, more careful, mindset*.

TL;DR

Eventually I hope to replicate @geniusintraining's ball and beam device. The code is more or less written in my head, although I will be coding the PID equation also, as I am too cheap to buy RSLogix 500.

The next step will be figuring out how to get the 24V PWM signal down to 4.8-6V; from my reading that servo should take its motive power and current across the other two wires (gotta figure that out too; I think four AAs might do the trick), and the PWM positioning signal will be low current.

Thanks again!

* I did once manage to make some sparks by poking a wire from DC 24V+ briefly into the grounded DC COM terminal instead of the input terminal next to it as intended. Apparently the laptop charger has a current limiter that dropped the voltage; the PLCs rebooted after I jumped back. It's good to be smart, it's better to be lucky. Now there is a piece of duct tape over the DC COMs (Fool me once, ...).