On a Analog output instrument in this case a fisher valve can you connect the Emerson 475 hart communicator direct to the valve (DVC6200) with no 250-ohm resistor? I know it doesn't hurt to use one but was wondering. Also I know why you use the 250 ohm resistor but am under the impression you can use up to 1100 ohms if need be which would operate between 4.4 and 22 vdc instead of 1-5vdc I understand you would rather use 250 ohm however I'm wondering if that is why you could hook up direct to a Analog output travel valve cause you would have a higher resistance internally through the instrument then 250 ohms at any given time. Let me know if I am on the right track or if anyone has any input. Thank you. I understand most analog input cards have 250 ohms built in strictly wondering on analog output.