I am trying to acquire transient voltage signals with a PCI-6110 board, sampling at 5MHz. When I examine one channel of an input signal (from an optical sensor, with its own internal op amps) using the sensor's BNC cable to high-impedance input of an oscilloscope, the ~200mV signal is clean. When I plug the same signal cable into a BNC-2110 BNC I/O connector block, which feeds the PCI-6110 DAQ card, the resulting signal has added noise in the form of small transient ringing which remains steady and synchronous with the input signal. The total signal duration is of order 10 microseconds. It is somewhat coarsely sampled, but my problem is with the added ringing noise. The BNC cable comes directly from the sensor, is about 2' long, and cannot be shortened. The digitized samples are synchronous with transient signal, since the sensor stimulus is being driven by trigger output from the PCI-6110.
I welcome any suggestions on possible causes or solutions to this noise problem. I hope not to have to build or obtain some custom high-speed buffer input amplifiers.
