I am using HoneyWell Sensors with my USB-6281 to measure pressure vs time. While calibrating the sensors show no problem. It was only by fluke that I noticed the sensors were behaving strangely. I measure a device that regulates fluid pressure and have a system in which a constant flow of water is pumped through this device. When the water is being pumped and the device is operating properly the problem is not noticeable. The water pump has about 4 hours of steady flowing water being pumped through the device. One day I left the pump and data running over night. It was easy to see that roughly at about 4 hours all the pressure began to dip low indicating that the water had run out and there should be no more pressure stimulus. But I started seeing peaks and valleys throughout all 10 of my sensors, sensors that had no active pressure being applied. I began to consider the design of my water pressure system so I decided to run a test over night with absolutely no pressure at all, that is to say closing all channels to any stimulus. I found the same kinds of peaks and valleys occurring through all 10 channels again. These peaks and valleys occur similarly throughout all channels save for a scalar value differentiating from channel to channel.
I have spoken to NI Application Engineers over the phone and they have run a bunch of tests resulting in finding no problem. There has been speculation of the occurrence of "ghosting" which doesn't seem correct since my sample rate is 1 Hz. There was also the suggestion that this particular model has only 1 ADC and that may be the issue, also an alliteration to ghosting. Maybe a DAQ card in which there is 1 ADC per channel would be the solution but it was recommended to keep that as a last resort as this problem should be fixable without purchasing a new card.
I am using this DAQ card in conjunction with a different card to power the sensors. The grounding is done through both cards and ofcourse the data is in the NI card. There is no problem with the wiring configuration but the problem continues to persist when given static pressure, whether during the day or night.
I am looking for recommendations of sensors that will work well in condjunction with the USB-6281 and will give consistent pressures given a period of static pressure. Has anyone heard of this problem occurring with these sensors per say or just the problem in general? Ideally I would like the accuracy of these sensors to be within ± 0.1 mmHG. The HoneyWell Sensors I use are 1 PSI analog single ended.
Thank You