How Are The B/E/M/S Calibration Procedure Values Calculated?Primary Software: Calibration ExecutivePrimary Software Version: 1.0 Primary Software Fixed Version: N/A Secondary Software: N/A
Problem: I am looking at the B/E/M/S Series Calibration Procedure for NI-DAQmx document and the Upper Limit and Lower Limit values do not seem to match the Accuracy Information from the Detailed Specifications for the actual DAQ device. Which document is correct? Solution: The B/E/M/S Series Calibration Procedure for NI-DAQmx document has the Absolute Accuracy at Full Scale already calculated for the user, but this value can be determined from the device specific Detailed Specifications as well. For this specific example we will be looking at the PCI-6071E.  Figure 1 - Absolute Accuracy from Detailed Specifications for PCI device If you take the Initial Nominal Range, in this case 0.05V and multiply by the 0.0714% (% of Reading for 1 year) then add the Offset of 0.049mV plus the Averaged Noise + Quantization (mV) value you will get the Absolute Accuracy at Full Scale (mV) value. (0.05 V * 0.000714) + 0.000049 V + 0.000007 V = 0.0000917 V or 0.091 mV (The Absolute Accuracy) The Temp. Drift is not taken into account as the B/E/M/S document is assuming that you are calibrating / operating the device at the calibrated temperature. If we now look at the B/E/M/S Calibration Document then we can find the table in Figure 2 on Page 50 of that document.  Figure 2 - 6071E Analog Input Values from B/E/M/S Calibration Manual Now when looking at the B/E/M/S document let’s take a look at the -0.05 to 0.05 V (Pos FS Location): They take a test point and get a value of 0.049900. Looking at the 1-Year Limits we will pull back the value of the Absolute Accuracy at Full Scale (mV) of 0.091mV. We take the initial point of 0.04990V and add/subtract 0.000091 we can get the 1-Year Limits and the Lower Limit (V) value of 0.04981 and an Upper Limit (V) value of 0.04999. The last digit gets rounded off, but that is how the calculations are made.
The Pos FS Location values and the Neg FS Location values are calculated the same way. To calculate the 0 Location Value it would be similar to how to calculate the Pos FS and Neg FS values, except the Value to multiply by the percentage will be 0. So the math looks like the following: If you take the Initial Nominal Range, in this case 0V and multiply by the 0.0714% (% of Reading for 1 year) then add the Offset of 0.049mV plus the Averaged Noise + Quantization (mV) value you will get the Absolute Accuracy at Full Scale (mV) value. (0.0 V * 0.000714) + 0.000049 V + 0.000007 V = 0.0000917 V or 0.056 mV (The Absolute Accuracy) By rounding it will equal to 0.06 mV or 0.00006V. Related Links: B/E/M/S Series Calibration Procedure for NI-DAQmx Attachments:
Report Date: 04/02/2009 Last Updated: 12/29/2009 Document ID: 4W19UKSH |
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