Setting Output Voltage on AB ControlLogix

bcraig

Member
Join Date
Jun 2003
Location
Syracuse, NY
Posts
4
I am new to PLC's and am attempting to spec one to replace some obsolete custom hardware. One of the early problems that I have encountered is that the discrete signals that I need to provide to the "outside world" are +28VDC rather than a standard voltage.

I have been looking at documentation on several web sites and found that AB's ControlLogix Digital Output Modules supposedly will handle a 28V output, but I have no idea how to control the voltage that these modules put out. Is it a setting on the power supply?

My alternative it just to use a relay module and an independent power supply, but this would not be as "clean" a solution.

If anyone knows, please respond. Thanks.
 
bcraig said:
I have no idea how to control the voltage that these modules put out. Is it a setting on the power supply?

My alternative it just to use a relay module and an independent power supply, but this would not be as "clean" a solution.

You will have to supply the power via an external power supply if you use an contact output card or a transistor card. Power that drives the outputs DOES NOT come from the PLC backplane.
 
If I needed 5 V output, would that come from the backplane, or is are all the outputs from the output modules supplied by an external source?
 
You're looking at this all wrong, Craig. A discrete output isn't a device that takes power out of the PLC and sends it to the world. A discrete output is essentially a switch that the PLC opens or closes to send status information out from the control logic and turn loads on or off.

PLC discrete outputs almost always switch voltage that is supplied by a power source external to the I/O card. There are two ratings of particular significance that must be checked against the load requirements that the I/O is switching.

First is voltage range. The voltage must be within range to prevent short circuits through the output device to ground or the load, and in the case of some solid state outputs the voltage must be in the proper range to insure correct switching action.

Second is current range. If the load current exceeds the rated current of the output teh output will be damaged by overheating.
 
The +/- 10 volt outputs from servo cards are generated by DC to DC converters that get their power from the back plane.

Peter,

I don't know about servo cards, but with analog output cards you can select between power from the bus and power from the front connector, which is preferrable.

Kind regards,
 
Ya, but

bcraig said:
I have encountered is that the discrete signals that I need to provide to the "outside world" are +28VDC rather than a standard voltage.

The original question was in regards to discrete outputs, not analog or servo cards.
 
The word "persnickety" comes to mind...

Yeah, or should I say "Ya", we get it Peter... :rolleyes:

As 93lt1 pointed out, notice the O-R-I-G-I-N-A-L post... đź““

To help you out, I've highlighted some of the more 'important' words... :D

Originally posted by bcraig
I am new to PLC's and am attempting to spec one to replace some obsolete custom hardware. One of the early problems that I have encountered is that the discrete signals that I need to provide to the "outside world" are +28VDC rather than a standard voltage.

I have been looking at documentation on several web sites and found that AB's ControlLogix Digital Output Modules supposedly will handle a 28V output, but I have no idea how to control the voltage that these modules put out. Is it a setting on the power supply?

My alternative it just to use a relay module and an independent power supply, but this would not be as "clean" a solution.

If anyone knows, please respond. Thanks.

Sure sounds discrete to me!... :nodi:

beerchug

-Eric
 
Last edited:

Similar Topics

Does anyone know how to set the output window on-off values on the fly without having to inhibit the module? I could of sworn when I first started...
Replies
11
Views
2,342
Hello all, On occasion, I need to manually set a PID control variable's initial output when the process is first started- say a bump to 100% to...
Replies
3
Views
3,600
I'm using an Automation Direct SL4848-CR to control stuffing pressure to a centrifugal milk separator. The problem I'm trying to overcome may be...
Replies
2
Views
2,500
Hi, Micrologix 1000 Dumb question but I can find the answer anywhere Taking the 24v DC power to the output side, can I set it to output 9v...
Replies
6
Views
1,464
Hi, I am new to PLC and wish to prgram a sequence where a single push button is used to set and reset an output upon each press without...
Replies
3
Views
1,916
Back
Top Bottom