Dear All, I have 4 pressure transmitters, 4 temperature transmitters with output of 0-10 Volt or 4-20 mA. Also I have 2 flow meters with output of 4-20 mA. I have two options:Either to get all the signals in mA and connect them to two C modules NI 9203 OR I can get 8 sensors with 0-10 V and then I can use for example NI 6218 where I can connect these signals using the differential configuration. While the last two signals (of the two flow meters) are to be converted using SSC components to yield Volt output so that I can connect them to the same card. Which solution is better regarding the signal noise ? Some one told me that NI 9203 does not support differential configuration as the mA signal does not obtain noise like the Volt signal so it does not need differential configuration. Also NI 9203 has 0-20 mA input range and the sensors output is 4-20 mA ......... Is there a problem ? Please advise ....... Yours,Ehab

Hi Ehab, Do you mean that you have the option between voltage and current transducers, and would like to know which is best? A 4-20 mA current loop is inherently less sensitive to voltage noise. 4-20 mA sources have a much higher output impedance than a shunt resistor, so the vast majority of the noise is dropped across the source. The following application note from BAPI and our own Developer Zone article both give a good overview of the subject: Understanding 4-20 mA Current LoopsCurrent Measurements: How-To Guide As far as the 0-20 mA vs. 4-20 mA, you won't have any problems here. One reason 4-20 mA is used commonly for sensors is that a 0 can be used to indicate a bad (open) connection. When taking a voltage measurement, the best way to reduce noise is to measure differentially, with your connections being made with shielded-twisted pair wires (wikipedia link). The idea here is that any atmospheric noise would affect both the + and - ends of your signal. Since you are measuring differentially, the noise would cancel out. You will likely be fine in either case. If you use the 6218 you can provide your own external shunt resistors to measure current, while using the other channels to measure voltage. See the article How to Build a Current Loop System with Isolated M Series. It appears to not be updated for the 6218, but this board provides the isolation recommended for measuring current. The 9203s have this built-in to the board and are meant specifically for measuring current. Other recommended reading would be Field Wiring and Noise Considerations for Analog Signals. When setting up this system you'll need to make sure everything is grounded properly (no ground-loops, floating connections, etc.). -John