11-29-2010 04:20 PM
Dear NI Tech Support,
We are working on some novel micro-fluidic flow sensors and are using one of the National Instrument PCI DAQ Cards (PCI-6020) for our data acquisition. It looks like we have a working flow sensor, but our data raises some questions. The signals appear to correlate well with flow, but they are very low level, on the order of 100mV and we expected signal levels on the order of 1V.
The National Instruments PCI-6010 DAQ data sheet (also attached) specs the input resolution at 16 bits Þ5V/216 = 76mV. Also the data sheet specs
the input signal range to be ±0.2V to ±5V. Whereas our data set appears to be resolving voltage differences as small as 1 mV.
QUESTION #1: Does the DAQ use a high resolution oversampling (i.e. Delta Sum) converter?
QUESTION #2: Can this DAQ can actually resolve 1 micro Volt signal levels? 1mV?
In addition to being low-level, the voltage levels are negative. I believe that the DAQ has dual supplies delivered from the computer through the PCI connector. Still, we're powering up the sensor via a single supply so we shouldn't be seeing negative signals.
QUESTION #3: I'm guessing that the negative values are a result of the DAQ's offset voltage error?
Thank you in advance,
TWIA LLC
11-30-2010 01:17 PM
Hello TWIA,
The NI 6010 is not a Dynamic Signal Acquisition Device (DSA), therefore it does not use Delta-Sigma Converters. To better answer your questions, are you using bridge-based sensors? These sensors return values in mV/V i.e. the ratio of the output voltage to input voltage, or excitation. If this is the case, there is a different approach to measure these readings using an analog input device vs. using bridge-based data acquisition devices. Also, using a handheld DMM what values do you observe at the output of your sensors?
Best regards,
Ali M
Applications Engineer
National Instruments