ShaunDustin
2008-06-27 22:40:09 UTC
I am using a bank of 17 Omega DP24-pH meters in conjunction with several cDAQ 9172 chassis and 9203 current modules. The problem we are running into: If I put two or more pH probes into the same solution then hook the current output from the meters to the same 9203 block, the readings go nutty. One will drop to a decimal value around zero, and the other will go up. If I short across the current output terminals to eliminate the influence of the NI equipment, readings return to zero. The meters are fine if I don't connect them to the 9203--I have put up to 6 in the same solution and they read just fine, so I don't believe it is probe interference, it has to be output signal interference, right? The output signals are wired into the module in blocks 0-7, with the common grouped together and wired into 9. Any ideas on how to resolve this would be appreciated. I must be missing somthing in the wiring?