Should The Absolute Accuracy Of A Measurement See A Constant or Dynamic Offset?

Updated Jan 18, 2019

Reported In

Hardware

  • Multifunction I/O Device

Issue Details

I found the equation for Absolute Accuracy of measurements on NI's website, but how will I observe this in my data?

Solution

The equation for absolute accuracy has 6 parts.
Absolute Accuracy =± [(InputVoltage x %ofReading) + (VoltageRange x Offset) + SystemNoise +TemperatureDrift]
  • Input Voltage
  • %ofReading
  • VoltageRange
  • Offset
  • SystemNoise
  • TemperatureDrift

Where:

  • Input Voltage is the voltage range the device is configured for. For example, for +- 10V, Input Voltage = 1
  • %ofReading is a raw % accuracy based on the input gain. This accounts for gain error
  • Offset is the maximum offset error. Many times, this offset can be in ppm instead of % so in order to change this into %, use this conversion: 1% = 10,000 ppm
  • SystemNoise is the error introduced to the measurement by the device itself. This will often depend on filter settings or whether a single sample is taken as opposed to multiple samples being averaged
  • TemperatureDrift** =± [(InputVoltage x %ofReading/ °C) + (%Offset/ ° C)]
For constant measurements, a constant offset should be seen across data points from the Gain Error and Offset Error components of Absolute Accuracy. The Noise Uncertainty will give dynamics variations to data points across data points. These are for steady state conditions where settling time is ignored.

Sampling Rate is also not a function of absolute accuracy, however for multiplexed DAQ cards, a specification will be given on the specification sheet for settling time under dynamic considerations.

WAS THIS ARTICLE HELPFUL?

Not Helpful