Analog Outputs

[AlmostHuman]

Hello!

Let's say that I already have hardware but it does not meet my current needs (not in papers at least).

I have V570 with V200-18-E2B snap-in. The problem is that I need an analog output that ranges from -5V to 5V, but I only have two analog outputs that run from 0-10V.

So, here's my question:

Is it possible to connect VOut 0 to positive terminal of control valve (valve that i need to control with -5V to 5V) and VOut1 to negative terminal of that valve - thus completing circuit through Analog outputs (making one output source other sink)?

Note: This can be done with one 0-10V output and one relay with two pairs of NO and NC contacts, but the process requires fast and frequent switching between positive and negative values on the output...

Thanks in advance!

PS

If I missed forum section please let me know.

[Simon]

The short answer to your suggested fix is "no".

The keyword that needs to be understood is "galvanic isolation".

The analogue ouputs on the E2B share a common. If they were fully isolated from each other you could use one output for the positive, connected the normal way. For the negative you would need to connect the second output in reverse. This is only possible if the two outputs have their own commons (0V) AND are fully galvanically isolated from each other. The relevant aspect of Galvanic isolation in this case means no continuity between their 0V terminals. THis is not the case with the module you have. You would also need the valve inputs to be fully isolated.

IF the input of your valve is galvanically isolated, then you could use a voltage divider circuit (with resistors) to create a "virtual" 0V point that is in the middle of your 0...10V span. This requires that the 0V input on the valve is not connected internally to the valve housing or the 0V of the valve power supply.

The third option is to purchase an EX-A2X and IO-AI4-AO2, which gives you a +/- 10V analogue output.

Another option is to use an external analogue isolator, configured for 0...10V input and -5...+5V output.

[AlmostHuman]

Thaks Simon,

I was hoping that lack of galvanic isolation would help me in this case (so the current can complete a circuit through:

VOut0 --- +valve --- valve coil --- -valve --- VOut1 --- internal generator --- 0V (AOut1) ---lack of galvanic isolation --- OV (Aout0) --- Internal generator --- VOut0)

But since I'm completely unaware of hardware implementation of these internal generators, and PLCs altogether, I will not question your judgement

Since I'm over my budget with this project I'm going to aim at the cheap, safe solution which sould be analogue isolator that you mentioned as an option.

Thank you again!

[Simon]

Hi, I see where you are coming from. I can see it may work the way you say, but that will need the valve signal input to be fully isolated. So you would set Vout1 (connected to -valve) at 5V to give a reference point, then raise or lower Vout0 (connected to +valve) to give -5V...+5V relative to the Vout1.

However I still think an external isolator is the most robust method, and simple to understand for you and anyone else who needs to maintain the system.

[Simon]

Just a further thought on the use of two outputs to provide the +/-5V, the configuration discussed would require current to flow the wrong way through one or the other output. I am not sure the outputs would like this. It will either not work, or possibly damage the output(s).

Once again, a good reason to use the external isolator.

[AlmostHuman]

It will either not work, or possibly damage the output(s).

Once again, a good reason to use the external isolator.

Thank you very much! I will not "play" with a $300 equipment to save on $20 level translator.