I don't know if such a device consists but mostly if I can think of it it is available :)

Can anyone recommend me a stand alone DIN rail mounted A/D converter with at least 8 digital outputs that can be controlled with a 4-20mA signal?
I was thinking of controlling it with a 255 step signal that represents the equivalent binary code.

As you can guess, a customers machine is at it's CPU maximum I.O capacity and he needs 7 extra outputs but only has 1 analog spare....
I know upgrade the CPU you would say but if there is any other solution this customer will be very happy...

See links below.
Not 8 outputs but four. Can be connected in series if your analog output will support that. Also the below devices have an aux analog out to drive another device. Maybe be a solution for your application.

Scroll down to "SPA"
http://www.miinet.com/products/sg_alarm.shtml

http://www.miinet.com/cgi-bin/download.pl?...;form=quick_reg

Weidmuller used to offer a device which took an analog input and gave two limit outputs. I don't know of one with 255 steps.

You could use a Moeller EASY 821-DC-TC

It has 10 bit analog inputs (0-10V) and 8 DC transistor outputs.

And it mounts on a din rail

http://www.moeller.net/en/products_solutio.../easy/index.jsp

You can program it through the display but might be easier to use the software...

That's a cool idea and it sounds interesting but doesn't that make it unnecessarily complicated and hard to troubleshoot? Imagine trying to figure out why 2 out of the 8 outputs aren't working when it's being fed from and analog signal. That's a downtime disaster waiting to happen if you ask me.

I would think some kind of communication option would be better. 232 or 485 to another small plc or something would be much easier to troubleshoot and probably would be much more reliable.

Not to be argumentative but I have to completely disagree, a communication link would be a lot more complicated and a lot less reliable. IMHO of course. Call me old fashion but comm links are for data exchange, messages, HMI,SCADA not for critical control.

I understand where you are coming from. I always think of it with our conditions taken into account. Our entire plant is washdown so everything eventually gets wet. Trying to troubleshoot a 4-20ma signal that has corroded wires and such would be a real nightmare and also I would think that depending on what you're controlling there could be a personal safety or machine safety element in that.

Say your 4-20 mA transmitter is not working correctly or gets wet or has corrosion that is having an effect on the 4-20 mA signal, well then you're binary that you're trying to send is not going to be right so you're outputs are not going to be right. You could be turning something on that's not supposed to be on or vice-versa.

PLC to PLC communication on the other hand will either work or it won't work. If it's not communicating then you won't get any outputs. Plus communication works inherently well with binary information because, basicly, that's what it is.

Maybe that isn't an issue with what he is doing, but I think that's something to think about.

P.S. I like the debate, it's cool that everyone can voice their opinion one way or the other. That can't always be said with forums like this one.

Hi guys thanks for the replies.

I see where you are coming from with potential faults and the dangers of them but these outputs will just drive some indicators so no real hazard involved should the analogue signal be bad. Further more the module will just sit next to an analogue output unit in a control panel so no cable or corrosion issues.
Although I see some possible options I don't think that what I had in mind is available. I know a din rail mounted signal converter from Phoenix contact that uses 4 digital inputs and their binary state to drive an analog output 0-10V. I am just looking for the exact opposite....

i would go for this moeller thing as you can do the programming very easy and cheap. it has drivers on board for your lights.
else it can be done in 5 volt with some ttl circuits, however this has to be made special.

otherwise you colud use this analog signal as a serial output and have a small plc do the conversion for you.
just use standard serial type only slower.
another bustype is iic this can be put into a single ic and it has 8 outputs, however it does need two outputs from the plc, (or 4 signal values.
i work a lot with wago so cheap and versatile is possible.

If it were me, i would take a 20 I/O CP1L. Thats cheaper than many specialized signal converters.
I think all CP1L have a 8 bit analog (0-10V) input connector, below the USB connector.
Well, i know, it is possible only if your analog output can be 0-10V, or 0-20 mA but if your analog output is from an Omron PLC there is no problem to do it.