BS: I got these spare Analog Inputs ...

BrainStorm

And I was thinking, "What can I use these for ... What can I sense with them that would improve reliability the most"

The answer to that question is power supply health on my machinery. Our techs seem to waste the most time finding a bad 5vdc, 12vdc, and most commonly 24vdc power supply as the cause of some failures.

I need a circuit that will convert 24vdc to say, 5vdc. Then 12vdc should be 2.5, and 5 would be 1.0417. Then alarming/troubleshooting can be automated along with orderly shutdowns.

I have one supply that commonly goes to 40vdc with some ripple when it fails. I don't want to blow up a channel if this happens. It would be connected to a SLC-1746-series 8 channel input. I forget the p/n, but I can get it later.

I am dealing with all varieties of AB inputs. Mostly PLC5 1771-IFE/C, 1746-various, 1756-IFE, and some compaclogix, don't know the p/n.

All participation and suggestions welcome.

OkiePC

Basic voltage dividers with series resistors.

No need for complex power supplies.

My first thought was just to connect sensing wires to the channels through a voltage divider circuit. Since the input impedance/resistance of the analog channels is quite high, I should be able to ignore it my calculations, right?

Thanks,
Paul

Edit: does this look right?

I would use transmitters, something like this.

http://www.laurels.com/transmitter-4-20-dc.htm

Mickey, that would definitely protect the expensive analog channels.

I plan to add fusing to my sensing circuit and go with the cheap method, since our budget is tapped, but for future modifications when we get some cash, the transmitters look like the way to go.

Thanks

Okie,

Exactly what I was thinking.
Fuse it & you're banging good to go.

Okie,

Exactly what I was thinking.
Fuse it & you're banging good to go.

Click to expand...

Cool.
Thanks all.

I'm probably missing something here but...

How about LEDs with appropriate dropping resistors wired in parallel? 'DC at a glance - but, no AC component at a glance'. 20 MilliAmps, big deal
That would only show voltage present, not actual. Since TTL likes 5VDC ± 5% then... I like my 5VDC to be 5.05v AT SOME RANDOM CHIP
And of course, the 24VDC can be 22 to 28 so...

Most CNC cabinets have indicator LEDs like that on their various supplies. Just a thought.

Rod (The CNC Dude)

My goal is to display power supply voltage on the HMI. I have some antique servo controllers that start acting up at about 4.65v. I too like them set at 5.05.

I also have some 24vdc supplies that occasionally suffer from low voltage due to shorts. When they get below about 18vdc, I have problems. I can trigger alarms based on the value, and stop the process before scrapping product. It will also give the techs a quick view of the voltage to save them time when just checking things out.

I am just trying to add a cheap solution for what is often a time consuming troubleshooting process. In most cases, there are spare wires I can use as sensing wires, add some fuses and resistors to the terminal strips, a little keyboard magic, and Voila: Another tool to maximize production.
Okie