Hello all,
I have an instrument (wired by someone else) that has 2 flow controllers and one flow meter. The controllers are controlled via a 9263 AO module (one channel for each controller), and the reading of the controller flow as well as the flow of the meter is read by 3 channels of a 9215 AI module. I recently encountered an issue where the signal of the meter exhibits a low frequency high amplitude oscillation (amplitude of about 0.1 V with no flow). I tried some troubleshooting and managed to isolate a possible cause. In the original wiring, the COM of the AO module is jumped to the AI- for both controllers. If this connection is broken, the reading from the meter becomes as expected. However, I feel that this would then render the controllers useless since I would not be able to control them (There is no wire going from the AO COM directly to the controllers). The strange thing is that this instrument has worked for several years with this wiring and it's only recently that this has been observed. Any insight is welcome. I am attaching a quick diagram as to how the modules are currently wired with noise and without noise as well as a plot of what the signal looks like for an expected reading of 0 volts (no flow) with and without the oscillation.