4-20mA always 1-5vdc?

When a PID controller (non loop powered) generates a 4-20mA is the voltage always 1-5vdc?
Reason for the question is we have two control valves that take either a 4-20 or 1-5vdc(you can use one or the other). We want to use 1 4-20mA signal to drive the two control valves, something I have done in past. The valve manufacture told us dont run them in a loop but run them parallel meaning on set of wires goes to the 4-20input on one valve and the other set goes to the 1-5vdc input on the second valve.
Now I dont see a reason this wont work, but I am unsure of the voltage coming from the controller....In fact I am not sure what the controller is since this whole thing is miles away!
SO you may ask why not just hook up both valves in series with a single 4-20mA, I am asking that to and this is what I got! I have a feeling the impedance in the valves are to high for a single controller to drive two valves at the same.
thanks for the help
stoop-

No. The voltage (across any specific load) on a current loop is dependent on the loading resistance on the loop, and the individual series element you are looking across.

It is just typical that the 'Standard' load resistance of a device is 250 ohms, but that isn't a true standard.

No, a 4-20mA signal does not necessarily have to produce 1-5VDC at the end device. The only way it will is if the loop resistance of the driven device is 250 Ohms.

In your specific case the valve guy has some specific knowledge the rest of us don't. That knowledge is that the current input to the valve will always have a 250 Ohm resistance. The 1-5 VDC input likely has a high kilo-Ohm resistance so putting that in parallel with he current input device won't change the driven resistance by much.

It is possible that the current input to the valve isn't completely isolated. If this is a tree-wire device or a four-wire device with the source and signal commons tied together you can't tring them in series even if you wanted to.

Keith

You might also consider a 4-20ma splitter. See link below for one such option.

http://www.miinet.com/products/data_sheets/ect_din.pdf

I think I am going to the splitter, this seems to be the safest thing to do.
SO I want to make sure I understand, the voltage the controller will output is dependent on the load in the loop. So Higher the load the higher the voltage (till a point), the controller just tries to make the right mA signal.
Thanks so much for the help!