About anti-inference in NI C-series modules

[beston]

Hello everyone.

                     I have a compact  RIO 9031 and some C-Series modules,such as NI 9203.I kown there is a isolated ADC in NI 9203,and I want to kwown if the isolated ADC can have the function of anti-interference. And should I add  an additional isolation transmitter .And the system of mine works in an environments  with Strong electromagnetic interference.The data I measured is very volatile.What should  I do to solve this question.I am really need your help.

              Thank you all!

[rolfk]

As long as any common mode voltage on the wires doesn't exceed the isolation voltage of the ADC you should be able to make it workable.

What you will need to make sure of is that you only have one and exactly one ground reference point on the input side of the ADC. Yes you will need to make sure your analog inputs are somewhere ground referenced as strange as that may sound about using isolated analog inputs. Generally most sensors are somehow grounded in some way somehow and that is why you do often require an isolated analog input to avoid ground loops. But sometimes sensors are fully isolated themselves and are not actively connected to any other electronics, such as for instance thermocouples that are electrically isolated from the housing or if you mount the thermocouple on an electrically isolated surface. Also you might use sensors that have already built in electrical isolation to the measurement signal. If both sides are no ground referenced at all, you create a floating electrical network whose common mode voltage can easily float above the electrical isolation voltage that the isolation amplifier is specified for, due to electrostatic charges that build up and then you have periodic electric discharges into the isolation amplifier that will be measured as very high noise and in the worst case even could damage the isolation amplifier over time. So while an isolating amplifier is generally great, as it can be connected to just about any signal source, it may be sometimes necessary to ground that signal somewhere and somehow, if the sensor itself is also fully isolated. But within an electrical network (that could also mean within multiple sensors if the inputs are not individually isolated), you should always make sure that there is always only one single ground reference anywhere. Best is usually to do that in a star configuration if you have multiple signals on a single electrical network, that need to be ground referenced.