Frequency Error
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or Generation Accuracy Hardware: Multifunction DAQ (MIO), Digital I/O (DIO), Counter/Timers (TIO), Modular Instruments>>Dynamic Signal Acquisition and Analysis (DSA)>>PXI-4462, Modular Instruments>>Dynamic Signal Acquisition and Analysis (DSA)>>PXIe-4497, Modular frequency error ppm Instruments>>Dynamic Signal Acquisition and Analysis (DSA)>>PXIe-4496, Modular Instruments>>Dynamic Signal Acquisition and Analysis frequency of error in test (DSA)>>PXIe-4492, Modular Instruments>>Dynamic Signal Acquisition and Analysis (DSA)>>PXIe-4499, Modular Instruments>>Dynamic Signal Acquisition and Analysis (DSA)>>PXI-4461, Modular Instruments>>Dynamic frequency error definition Signal Acquisition and Analysis (DSA)>>PXIe-4498 Problem: How can I determine frequency error and frequency measurement or generation accuracy? Solution: Frequency accuracy (sometimes called timing accuracy) is usually given
Frequency Error Wiki
in parts per million (ppm) of the sample rate. This value depends on the device that you are using and can be found in the device's specifications. In addition to frequency accuracy (fa), frequency error (fe) is also something that you can calculate, using the equations below:Measured frequency (fm) = signal frequency (fs) ± frequency error deped frequency of error form (fe). Rearranging the above equation to solve for frequency error: Frequency error (fe) = signal frequency (fs) * frequency accuracy (fa). Examples:Consider a case in which you are measuring a precise 100kHz sine wave, using a device with a frequency accuracy of 25 ppm. The frequency error will be 100,000Hz * 25/1,000,000 = 2.5Hz. Therefore, the frequency accuracy is 100kHz ± 2.5Hz.Consider a case in which you are generating a 1kHz sine wave, using a device with a frequency accuracy of 50 ppm. The frequency error will be 1,000Hz * 50/1,000,000 = 50mHz. Therefore, the frequency accuracy is 1kHz ± 50mHz. Related Links: KnowledgeBase 1F5DD5KD: What Is Meant by the Stability of an Onboard Clock? Attachments: Report Date: 06/17/2002 Last Updated: 12/04/2014 Document ID: 2MGEUR2H Your Feedback! Poor|Excellent Yes No Document Quality? Answered Your Question? 1 2 3 4 5 Document needs work? Please tell us why. Please Contact NI for all product and support inquiries. My Profile | RSS | Privacy |
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Frequency Error Ppm Exceeds Tolerance
Print Overview How accurate are the frequency measurements you make using National Instruments counters? This document
Frequency Of Errors
describes three methods for making frequency measurements with NI 660x counter/timer devices and explains how to determine the accuracy of your frequency measurements. Table of Contents Sources http://digital.ni.com/public.nsf/allkb/2A0B9D3F365DEDEF86256BDB007354ED of Frequency Measurement Error Crystal Oscillator Error Measurement Error and Three Frequency Measurement Methods Which Method is Best? Calculations 1. Sources of Frequency Measurement Error There are two sources of error in frequency measurements: Errors in the frequency of the crystal oscillator Measurement error The total measurement error is the sum of these http://www.ni.com/white-paper/3619/en/ two sources, or: Measurement Error = Crystal Oscillator Error + Measurement Error Back to Top 2. Crystal Oscillator Error The crystal oscillator we use on the PCI-6601 and PCI-6602 is rated at 75 parts per million (ppm) stability over temperature. The crystal oscillator we use for the PXI-6602 is 200 ppm, but when in the PXI chassis, PXI 6602 will automatically phase lock to the clock of PXI backplane, which as accuracy of 75 ppm. With phase locking enabled the PXI 6602 will have 75 ppm accuracy as well. 75 ppm means that for every 1 million Hertz, the frequency can be off by +/- 75 Hz. For a 6601 board, which has a 20 MHz oscillator, the error due to crystal used could be up to +/- 75Hz/1MHz*20= +/-1500 Hz. For the 6602 board, which has an 80 MHz oscillator, the error is +/- 6000 Hz. The 10 MHz Oven Controlled Crystal Oscillator (OCXO) on a 6608 b
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GSM_FRQ performs the frequency error measurement described in [1, 2]. The frequency error measurement is used to verify GMSK modulation accuracy. The GSM_PHS measurement can be used to perform the phase error measurement that is also part of the GMSK modulation accuracy measurements. Parameters Name Type Range Block Diagram System Diagram N/A GSM Vector Signal Analyzer GSM VSA Meter N/A X-Axis display List of options N/A Y-Axis display List of options N/A Display overall maximum Check box N/A Display cumulative average Check box N/A Display reference limit Check box N/A Result This measurement returns real values. If more than one display option is checked, multiple traces are displayed, with the first trace corresponding to the top-most checked display option. The X-axis display parameter determines what is displayed for the x-axis. For the power options, the x-axis values are in the log power units (dBm or dB) specified in the project options. The Y-axis units are determined by the Y-Axis display parameter. If Y-Axis display is set to "ppm" and the measured signal has a carrier frequency of 0, the results are displayed in Hz. Graph Type This measurement can be displayed on a rectangular graph or tabular grid. Computational Details This measurement must be connected to a GSM_VSA meter. The measurement compares the measured signal to the generated test signal from the VSA meter in several steps: 1. The phase trajectory (phase versus time) over the useful part of each burst is calculated for both the reference and the measured signal. The useful part of the burst starts halfway through the first symbol and continues for 147 symbols. The phase trajectory is calculated using the following: φ[i] = φ[i-1]+Δθ[i]+adj[i] φ[0]=θ[0] Δθ[i]=θ[i]-θ[i-1] adj[i]=-2π if Δθ[i]>π adj[i]=2π if Δθ[i]<π adj[i]=0; otherwise The adj[i] term is used to compensate for +/- π wraparound. 2. The phase difference trajectory is calculated by subtracting the phase trajectory of the reference signal from the phase trajectory of the measured signal: φDiff[i]=φMeas[i]-φRef[i]+φAdj[i] φAdj[i]=-2π if(φMeas[i]-φRef[i])>π φAdj[i]=2π if(φMeas[i]-φRef[i])≤-π φAdj[i]=0 otherwise The φAdj[i] term is used to compensate for +/- π wraparound. 3. The linear regre