1746-NO8I mA problem

Hello,

I have 3 of the same valve positioners controlling V-Ported valves to control the flow of our product with a user input.
Their wiring schematic has a +/- for 24 VDC, +/- for output feed back (to PLC input) and +/- for input feed back (to PLC output)

I have successfully made 2 of these work with little to no problems as I have wired and programmed many a-like valves. the power and inputs all worked on first go.

How ever, when I connect the third valve to my new output card (1746-NO8I) all of the other inputs on my card go a bit haywire, instead of being at 31200 mA they drop to 20000 mA. These are the 2 valves that are already working, and the third valve also wont go above approx 20mA. this only lets the valves open to about 40% and if it varies slighly it loses signal completely.

This is a new PLC card and the only other connections are to the two positioners. I havent had an issue like this before has anyone had this happen and have any suggestions?

Thanks

I am not following your units. That analog output card can only put out about 21.5ma max and the usable range is 0-20mA. Hopefully you meant the raw numbers (31200 and 20000 raw counts, not mA).

I think we need a more clear description of the problem. Haywire to me means all over the place, but perhaps you meant something else.

Sorry,

You are correct, I didnt explain this very well.
When I connect the third positioner with the output set to 31200 units, it gives me only about 15mA and this number varies. It should be giving me 20mA

It isnt always the same number when I connect it, it may be lower or higher on all 3 positioners but I am unable to get it to give me a correct output, at 31200 (20mA) I want it to be 100% open but the valve is taking it as I only want it ~60% open or something and I cant get it to control the flow.

The other 2 valves follow suit and then none of them can be controlled.

With the 2 current positioners the figure I put in corresponds to the output on the valve. ie. 31200 units = 100% open.

I am starting to think there is something wrong with the card after I connect all 3 valves to the output card it doesnt work. And I have tried different outputs also, all with the same result.

Unfortunately I cannot connect it to a card already being used as there is no spare and I dont have a testing PLC, I am testing live.

Do you have a catalog number or model number for your valve positioner? Post it if so.

Is the valve positioner configurable to accept voltage or current?

What is the input resistance of the valve positioner's current input?

Ok so posi 1 and 2 work. Hook up number 3 and it seems too much load and all 3 drop down a bit on mA.

I'd try 2 and 3 or 1 and 3 and see what happens. If all is good then you know it's not posi 3 causing issues but rather the load of 3 of them. If it does mess up then you know it's a bad posi 3.
I agree it's manual would.be helpful

Its a FESTO CMSX-P-S-A1-C-U-F1-D positioner.

I have tried 3 on its own, and still only gets 19% read open from a 20mA signal.
I then moved positioner 1 to 3 and got the same issue.
I have now connected them directly to the PLC to remove the field wiring as an issue and have the same problem.

Positioner 1 works fine when its on its field wires, but when its in positioner 3's location it has the same problem.

I am now going to wire positioner 3 into positioner 1's wires and see if it gets any issues.

too busy right now to follow this thread closely - but it "sort of sounds like" you MIGHT be overloading the PLC's power supply ...

you can check for an overload condition under the I/O Configuration feature - but be aware that you MUST (MUST!) tell the system which model of power supply you actually have (example: P4) ... in simple terms, the software can NOT automatically "read" the power supply model number ... open the power supply's door and get the model number off the sticker ...

if this doesn't help - you might try posting the ENTIRE project file (RSS extension) ... maybe the forum members can spot something in the scaling (etc.) that you're just overlooking ...

another WILD GUESS ... some models of analog output modules have a little switch on them - to select whether using backplane power - or an external power supply ... have you checked yours for a switch - and its position? ...

sorry if you've already eliminated any of this stuff ... as I said - I haven't been following this thread closely ... just GUESSING ...

good luck with it ... gotta go ...

Ron Beaufort said:

too busy right now to follow this thread closely - but it "sort of sounds like" you MIGHT be overloading the PLC's power supply ...

Click to expand...

I agree. It sounds as though the analog output power supply is becoming overloaded. Does the third valve operate properly when one of the other two valves is disconnected?