- Using a separate measurement device such as a DMM (Digital Multimeter) or Oscilloscope, verify that the signal is behaving as expected at the input terminals of the DAQ device. Also be sure the Oscilloscope is properly calibrated by checking whether the probe and other components are properly set up.
- This isolates the DAQ device as the error and ensures that the input signal is not being corrupted at some other point in the system.
- Calibrate the device.
- Offsets and measurement noise may also be caused by an analog to digital (A/D) converter that needs re-calibration. NI data acquisition hardware can be calibrated manually by running a self-calibration in NI-MAX, although this is not effective in all cases and the device may need to be sent to NI or a third-party lab for re-calibration.
- See Device Calibration for more information.
Troubleshooting Offset Readings
Offset errors can be caused by incorrect DAQ hardware settings, uncalibrated hardware, or unexpected DC leakage through the hardware. Follow the steps below to resolve each of these causes:
- If the DAQ hardware comprises of jumpers, ensure that the jumper settings specified in software (i.e. in Measurement & Automation Explorer (MAX) or NI-DAQ Configuration Utility, depending on your NI-DAQmx driver version) match the actual hardware jumper settings.
- This will affect how LabVIEW converts measurements. For specific information about device jumpers, refer to the device's user manual.
- Calibrate the device by following Performing DAQmx Channel Calibration in MAX Using Wizard.
- If using the device in LabVIEW, configure a Custom Scale to correct the DC offset. Refer to Create an NI-DAQmx Custom Scale Programmatically in LabVIEW for guidance.
Troubleshooting Incorrect and Noisy Readings
Noisy readings can be caused by incorrect wiring, environmental noise or insufficient sampling rates. Follow the points below to resolve each of these causes:
- Use shielded cables instead of ribbon cables in noisy environments, or when measuring mV signals in the absence of signal conditioning.
- Ensure that the signal is using the correct analog input mode (DIFF, RSE, or SE).
- Environmental noise may cause bad readings, especially if there are long wires (over 15 feet) between the transducers and DAQ board (or SCXI module). See Field Wiring and Noise Considerations for Analog Signals for more information.
- Sample at at least 10 times the signal's frequency, if possible.
- Bad readings are often caused by aliasing, which is in turn is caused by a sampling rate that is too slow. See Aliasing for more information.
- Note: it may be necessary to sample at even higher rates.
- If the device has user-programmable input ranges, verify that the selected input range minimizes noise and optimizes accuracy for your signal range.
- Find this information in the device's specifications sheet.
- Connect 50ohm termination to the input channel and acquire the noise floor data (background noise).
- It’s recommended to save these data as TDMS for spectrum processing or send it to NI technical support for troubleshooting purposes.
Returns and External Calibration
- If all other troubleshooting tips have been exhausted and the problem is still present, then the device may need to be sent to NI for testing and re-calibration.
- NI's data acquisition products are shipped with a document that guarantees operation within the stated specifications for a certain period of time (typically one year); known as the calibration interval.
- If the hardware has been owned for longer than its calibration interval, then it may be inaccurate. However, before returning hardware, first contact NI Technical Support to help with troubleshooting efforts. See National Instruments Hardware Repair or Calibration for more information.
If using a C Series module, check the NI Calculating Absolute Accuracy or System Accuracy
to confirm that the data acquisition hardware is up to the task that has been set.