National Instruments NI 5911 Input Ranges, Input Impedance

Chapter 2 Hardware Overview

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National Instruments Corporation 2-3 NI 5911 User Manual

the cable impedances you use. As a result, most of the noise voltage occurs

at the negative input of the PGIA where it is rejected, rather than in the

positive input, where it would be amplified.

Input Ranges

To optimize the ADC resolution, you can select different gains for the

PGIA. In this way, you can scale your input signal to match the full input

range of the converter. The NI5911 PGIA offers seven different input

ranges, from ±0.1 V inputs to ±10 V inputs as shown in Table 2-1.

Input Impedance

The input impedance of the NI59 11 PG IA is 1MΩ between the positive

and negative input. The output impedance of the device connected to the

NI5 911 and the input impedance of the NI 5911 form an impedance

divider, which attenuates the input signal according to the following

formula:

where Vm is the measured voltage, Vs is the source voltage, Rs is the

external source, and Rin is the input impedance.

If the device you are measuring has a very large output impedance, your

measurements will be affected by this impedance divider. For example, if

the device has 1MΩ output impedance, your measured signal will be 1/2

the actual signal value.

Table 2-1. Input Ranges for the NI 5911

Range Input Protection Threshold

± 10 V ±10V

± 5V ±5V

± 2V ±5V

± 1V ±5V

± 0.5 V ±5V

± 0.2 V ±5V

± 0.1 V ±5V

VmVsRin

RsRin

+

--------------------=

CBIHWum.book Page 3 Thursday, October 29, 1998 1:56 PM

Contents

Main Page Important Information Warranty Copyright Trademarks WARNING REGARDING MEDICAL AND CLINICAL 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 Connecting Signals Introduction to the VirtualBench-Scope Soft Front Panel Soft Front Panel Features Page Using the VirtualBench-SCOPE Soft Front Panel Acquiring Data Page National Instruments Corporation 2-1 NI 5911 User Manual Hardware Overview Figure 2-1. NI 5911 Block Diagram Measurement Fundamentals Differential Input Grounding Considerations Input Ranges Input Impedance Input Bias Input Protection AC Coupling Measurement Modes Oscilloscope Mode Flexible Resolution Mode Acquisition System Calibration Internal Calibration External Calibration Triggering and Arming Analog Trigger Circuit Page Trigger Hold-Off Memory Multiple Record Errors During Acquisition RTSI Bus Trigger and Clock Lines PFI Lines PFI Lines as Inputs PFI Lines as Outputs Synchronization A Specifications NI 5911 Acquisition System Page Acquisition Characteristics Accuracy Common-Mode Characteristics Filtering Dynamic Range Noise (excluding input-referred noise) Distortion Timebase System Triggering Systems Acquisition Modes Power Requirements Physical Operating Environment Storage Environment EMC Compliance Calibration Digitizer Basics Understanding Digitizers Nyquist Theorem Analog Bandwidth Sample Rate Vertical Sensitivity ADC Resolution Record Length Triggering Options Making Accurate Measurements Appendix B Digitizer Basics National Instruments Corporation B-5 NI 5911 User Manual Figure B-5. Dynamic Range of an 8-Bit ADC with Three Different Gain Settings Page Page C Customer Communication Electronic Services Bulletin Board Support FTP Support Fax-on-Demand Support Telephone and Fax Support Country Telephone Fax Technical Support Form NI 5911 Hardware and Software Configuration Form National Instruments Products Other Products Documentation Comment Form Title: Edition Date: Part Number: Mail to: Technical Publications Fax to: Technical Publications Glossary Numbers/Symbols A B C D E F G H I M N O P R S T V W Index A B C D E F G H I M N O P R S T V