# Measument Accuracy of U2004A Power Sensor

Question asked by smarteebit on Jun 2, 2014
We are using Agilent's U2004A power sensor to measure the output power of some signal generator. Before determining how accuracy output of the DUT is, we must know how accuracy the test instrument is. So we want to U2004A's accuracy of measurement.

From the datasheet of U2004A (5989-6278EN), we can see the "power accuracy" spec as shown Figure 1. It's +/-3.0% at 25+/-10℃.
+Figure 1 (Attached as a jpg file)+

But a note following it says:
+Figure 2 (Attached as a jpg file)+

From which it seems the accuracy of measurement should be "power accuracy" + "uncertainty", such as mismatch uncertainty, calibration factor uncertainty...

From website of Agilent we also got the spreadsheet of "U2000_U8480_Uncertainty_calculator_v8_web.xls", in which we can calculate the uncertainty of the power sensor. If I input the frequency (160MHz) and power (4dBm) of my application, I can get a uncertainty range of +0.155/-0.161dB.
+Figure 3 (Attached as a jpg file)+

My question is, does the uncertainty got from the spreadsheet includes the "power accuracy" spec? Can the range of +0.155/-0.161dB represent the accuracy of measurement when I am using a U2004A to test a 160MHz, 4dBm sine wave? Or should I use the combination of power accuracy and uncertainty (i.e. +/-3.0% + (+0.155/-0.161dB)) as the accuracy of measurement in my application?

Thanks a lot.