National Instruments NI 5911 Making Accurate Measurements

AppendixB DigitizerBasics

©NationalInstruments Corporation B-7 NI5911 User Manual

Forexample, consider the maximum interpolation factor to be 5. If the TDC

could outputvalues from 0 to 15, then each logical bin will contain three

physicalbins, as shown in Figure B-6.

FigureB-6. Relationshipbetween Interpolation Factor,Logical Bins, and Physical Bins

Making Accurate Measurements

Foraccurate measurements, you should use the right settings when

acquiring data with your NI 5911. Knowing the characteristics of the

signalin consideration helps you to choose the correct settings. Such

characteristicsinclude:

•Peak-to-peakvalue—This parameter, in units of volts, reflects the

maximum change in signal voltage. If V is the signal voltage at any

giventime, then V pk-to-pk =Vmax –Vmin. The peak-to-peak value

affectsthe vertical sensitivity or gain of the input amplifier. If you

do not knowthe peak-to-peak value, start with the smallest gain

(maximuminput range) and increase it until the waveform is digitized

usingthe ma ximum dynamic range without clipping the signal. Refer

to Appendix A, Specifications, for the maximum input voltage for

your NI 5911 device.Figure B-7 shows that a gain of 5 is the best

setting to digitize a 300 mV,1 MHz sine wave without clipping the

signal.

PhysicalBin

3Physical Bins = 1 Logical Bin

DesiredInterpolation Factor = 5

MaxInterpolation Factor = 15

Sample

Clock

LogicalBin

Contents

Main Page Important Information Warranty Copyright Trademarks WARNINGREGARDING USE OF NATIONAL INSTRUMENTS PRODUCTS Conventions Contents Chapter 1 Taking Measurements with the NI 5911 Chapter 2 Hardware Overview Page Taking Measurements with the NI 5911 Installing the NI 5911 Connecting Signals Page Acquiring Data with Your NI 5911 Programmatically Controlling Your NI 5911 Interactively Controlling Your NI 5911 with VirtualBench-Scope Using the VirtualBench-Scope Soft Front Panel Acquiring Data Soft Front Panel Features Page Hardware Overview Differential Programmable Gain Input Amplifier (PGIA) Differential Input Grounding Considerations Input Ranges Input Impedance Input Bias Input Protection AC Coupling Oscilloscope and Flexible Resolution Modes Oscilloscope Mode Sampling MethodsReal Time and RIS Flexible Resolution Mode How Flexible Resolution Works Calibration Internally Calibrating the NI 5911 When Internal Calibration Is Needed What Internal Calibration Does Why Errors Occur During Acquisition External Calibration Triggering and Arming Analog TriggerCircuit Page Page TriggerHold-Off Memory Triggeringand Memor y Usage Multiple Record Acquisitions RTSI Bus Triggerand Clock Lines PFI Lines PFI Lines as Inputs PFI Lines as Outputs Synchronization A Specifications Acquisition System Acquisition Characteristics Accuracy Common-Mode Characteristics Filtering Dynamic Range Distortion Timebase System TriggeringSystems Page Calibration B Digitizer Basics Understanding Digitizers Nyquist Theorem Analog Bandwidth Sample Rate Vertical Sensitivity ADC Resolution Record Length TriggeringOptions Random Interleaved Sampling Page Making Accurate Measurements FigureB-7. DynamicRange of an 8-Bit ADC with Three Different Gain Settings Page Page C Technical Support Resources Web Support NI Developer Zone Customer Education System Integration Worldwide Support Glossary Symbols A B C D E F G H I Page N O P R S T U V W Index Numbers A B C E F G H I M N O P R S T V W