Calculating Absolute Accuracy of the PXIe 4300 and TB-4300B

Updated Sep 5, 2018

Reported In

Hardware

  • TB-4300B
  • PXIe-4300

Issue Details

I'm seeing more of an offset with the PXIe 4300 when I use the TB-4300B instead of the TB4300. How do I calculate the accuracy of this card and terminal block together?

Solution

To calculate absolute accuracy for the PXIe-4300 and TB-4300B, please follow the below example.

Assume a PXIe-4300 with the TB4300B to measure a 200V signal. We will assume the following temperature conditions as well:
  • TempChangeFromLastExternalCal = 10 °C
  • TempChangeFromLastInternalCal = 1 °C
  • TempChangeFrom23C = 10 °C (this denotes the termerature the TB-4300B was calibrated at in the factory)

Use the following equations for calculating absolute accuracy:

Absolute Accuracy = Reading * (Gain Error) + Range * (Offset Error) + Noise Uncertainty + Reading * (TB-4300B Gain Error)

Gain Error = Residual AI Gain Error + Gain Tempco * (TempChangeFromLastInternalCal) + Reference Tempco * (TempChangeFromLastExternalCal)

Offset Error = ResudialAIOffsetError + Offset Tempco * (TempChangeFromLastInternalCal) + INL_Error

Noise Uncertainty = Random Noise * 3/sqrt(10000) 

TB-4300B Gain Error = TB-4300B Attenuator Tolerance + Attenuator Tempco * (TempChangeFrom23C)

When the TB-4300B is connected, the module senses that the ranges are now 30V, 60V, 150V, and 300V, so we will use the 300V range for calculations. The TB-4300B attenuates signals by a factor of 30, which means we'll use the 10V numbers from the accuracy table in the PXIe-4300 Specifications document. We can also compute the Gain, Offset, and Noise Uncertainty of errors of the PXIe-4300 using the information found in this document.  

The TB-4300B Gain Error can be calculated using the information in the TB-4300B Manual. These calculations are shown below:

Gain Error = 65ppm + (11.5 ppm * 1 deg C) + (5 ppm * 10 deg C) = 126.5 ppm
Offset Error = 33 ppm + (10 ppm * 1 deg C) + 76 ppm = 119 ppm
Noise Uncertainty = 30 * (208 uV * 3) / (sqrt(10000)) = 187 uV
TB-4300B Gain Error = 500 ppm + 5 ppm * 10 deg C = 550 ppm 
 

Noise Uncertainty is multiplied by 30 due to the attenuation ration of the TB-4300B. The absolute accuracy then calculates to:

Absolute Accuracy = (200 V * 126.5 ppm) + (300 V * 119 ppm) + (187uV) + (200 V * 550 ppm) 
Absolute Accuracy = 25300 + 35700 + 187 uV + 110000 uV = 171187 uV = 171 mV 

Additional Information

Attached to this article is an excel file containing accuracy calculations for the full scale range of the PXIe=4300 with the TB-4300B.

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